Published by Theosophical University Press in the 1940s as Number Eight of the Theosophical University Studies.
I -- The Pattern of Earth History
II -- A Resume of Geologic History
III -- The Cause of the Ice Ages
Graphs of Earth History
For the student of Theosophy the study of natural science holds a particular significance. He feels that true science is to be approached with reverence, since even the simplest operations of nature touch on the deepest and most recondite of teachings.
Astronomy, mathematics, geography, geology and anthropology, and other sciences were once taught within the sanctuary of the Mystery Schools, whence scattered fragments escaped, to be worked over and reshaped by minds largely ignorant of the deeper significance of nature's laws. At cyclic times, due to the materialistic trend of civilization, factual knowledge has been separated from its esoteric matrix, the deeper understanding finally surviving only as a thin stream of almost forgotten legendary lore. As an example, the heliocentric nature of the solar system, with the attendant knowledge of the globular form of the earth, its rotation upon its axis and yearly journey about the sun, was known to Pythagoras and Plato, but was lost or discarded soon after the time of these Greek sages and was revived only within recent centuries. Today we see everywhere signs of the reunion of material science with its forgotten source, the Mysteries of Antiquity.
We would do well to realize more fully that the teachings of Theosophy are in very truth a statement of the laws of nature, both of Universal Nature and of the visible, outer shell of nature which we see around us. The late leader of the Theosophical Society, Dr. G. de Purucker, has repeatedly stated that all things follow one law; that small cycles repeat on a small scale what larger cycles pass through on a larger scale, and that all things contribute to all things in a vast system of cycles, or wheels within wheels, throughout Universal Nature. On every hand minor cycles of lesser lives demonstrate truths we have been taught regarding the cosmos. On every hand there is evidence to prove the truth of the teachings we hold sacred. In this way we may know many of our Theosophical doctrines by our own observation and experience, and not alone because we have been told of them or have read of them.
Because of this cyclic interworking of all life the earth's history presents a fruitful field of study. Geology divides the history of the earth into eras, naming these from their characteristic forms of plant and animal life. In Theosophy, the periods of earth history are named for the races and continents, using the word continent in its archaic sense, i.e., as comprising all the lands, both great and small, above water during a certain period of time. Thus, during this present great life-period seven continents appear one after another. The third continent, often called Lemuria, was the home of the third Race and existed during the Mesozoic era. The fourth continent, identified with Atlantis existed during the Cenozoic era. The fifth continent -- our own -- includes all lands above water at the present time. A misunderstanding of the special sense in which the word 'continent' has been used by the occultist is responsible for much confusion in regard to Lemuria and Atlantis. Each continent comprises a system of islands, archipelagoes, and other land masses which, because of their size, are also called continents.
Each continent is thus, in one sense, a world in itself, which slowly gives place to other lands and to other types of life. For everywhere, throughout the ages, land is either slowly sinking or slowly rising, with at times sudden catastrophic submergences. The face of the world and the life on it are continually changing, now slowly, now rapidly, throughout geologic history.
In The Secret Doctrine H. P. Blavatsky states:
Species and genera of the flora, fauna, and the highest animal, its crown -- man, change and vary according to the environments and climatic variations, not only with every Round, but every Root-Race likewise, as well as after every geological cataclysm that puts an end to, or produces a turning point in the latter. -- II, pp. 262-3
There is a plan and purpose in nature, a plan which works itself out in a series of repetitive cycles of activity wherein the smaller cycle operates within the greater, and it within a still greater. As G. de Purucker says in Man in Evolution:
Nature repeats herself everywhere. She follows grooves of action that have already been made; she follows the line of least resistance in all cases everywhere. And it is upon this repetitive action of our great mother, Universal Nature, that is founded the Theosophical doctrine of the law of cycles, which is the enacting of things that have been before, although each such repetition, as said, is at each new manifestation on a higher plane and with a larger sweep or field of action. -- p. 217
To the ancients, the earth was a living being. Those who were privileged to enter the sacred mysteries learned of the cyclic rise and fall of continents, the changes of climate, the secret structure of the earth and its intimate relation to the racial history of man. In these schools of occult learning, emphasis was placed on the causal rather than on the phenomenal; on the living, consciousness-side of nature, rather than on the mechanical. These teachings were given in strict secrecy, and were referred to publicly only by myth and by allegory. Those who have the key can read, even today, by hint and allusion in the ancient epic and the folklore of all peoples, the story of the formation of our earth and the way in which the various life-waves peopled it.
By the ancient method of instruction there was an unfolding of knowledge from a central theme or plan, proceeding from the general to the particular. The geology and geography of today, on the other hand, present a technical and scientific study of earth structure, topography and history based on observed facts, but without presenting a purposeful plan. Many scientists, indeed, deny that any plan or purpose exists in nature, yet on every hand we find evidence to prove that they are wrong. For example, everything has a beginning or birth, a maturity, an old age, and death, with a new cycle of life rising as the old declines. We may see this symbolized in the divisions of human life, the four quarters of the day, the successions of the seasons: and we may draw an analogy between the childhood of man, the dawn of the day and the spring of the year.
Nature herself produces the proof of the Theosophical doctrines, which are simply statements of the inner laws under which nature works. These are universal laws, habits of nature, which are followed both by the great and the small. Little cycles repeat on a small scale that which great cycles accomplish on a large scale, and all interwork and move within still greater cycles. For instance, consider the Universal Solar System, within which is our solar system,
consisting of the seven sacred planets. Within our solar system is our earth planetary chain of seven globes, within which again, is our earth, Globe "D," now passing through its seven Rounds, and also passing through those smaller divisions of time which the geologists call eras, periods and epochs, with which the Theosophist associates Root-Races, Sub-Races and Family Races.
Theosophy states that there are seven globes in our earth system, only one of which -- our earth -- is visible. The life wave passes through these seven globes, making what is called a Round. Seven such Rounds compose a Manvantara, or great cycle of manifestation. We are now in the fourth or most material Round.
In Theosophical writings the Universal Solar System refers to all bodies within the solar system, both visible and invisible. Our solar system consists of the seven sacred planets of the ancients -- the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn, the Sun and Moon being named as substitutes for two secret invisible planets.
During any reimbodiment of a planetary chain there is a long formative time during which the life-wave of the mineral kingdom prepares each globe in its turn for the vegetable, animal, and human life-waves to come. Beginning with the highest globe and proceeding downward from globe to globe, for a time the mineral kingdom is the focus of vital forces and is the dominant life of the planet. In The Mahatma Letters, page 94, the Master K. H. says, speaking of the beginning of a Manvantara:
Now the life impulse reaches "A" [Globe A] or rather that which is destined to become "A" and which so far is but cosmic dust. A centre is formed in the nebulous matter of the condensation of the solar dust disseminated through space and a series of three evolutions invisible to the eye of flesh occur in succession, viz., three kingdoms of elementals or nature forces are evoluted: in other other words the animal soul of the future globe is formed; . . . The three evolutions completed: palpable globe begins to form. The mineral kingdom, fourth in the whole series, but first in this stage, leads the way. Its deposits are at first vaporous, soft and plastic, only becoming hard and concrete in the seventh ring.
Regarding the Rounds in each Manvantara, G. de Purucker has said, "There are tremendous geologic and volcanic convulsions opening the drama of a Round on each Globe, ours included."
In The Secret Doctrine H. P. B. vividly describes the preparatory activity at the beginning of a Round:
Our globe being convulsed each time it reawakens for a new period of activity, like a field which has to be plowed and furrowed before fresh seed for its new crop is thrown into it -- it does seem quite hopeless that fossils belonging to its previous Rounds should be found in the beds of either its oldest or its latest geologic strata. Every new Manvantara brings along with it the renovation of forms, types and species; every type of the preceding organic forms -- vegetable, animal and human -- changes and is perfected in the next, even to the mineral, which has received in this Round its final opacity and hardness; its softer portions having formed the present vegetation: the astral relics of previous vegetation and fauna having been utilized in the formation of the lower animals, and determining the structure of the primeval Root-Types of the highest mammalia. -- II, 730
At the beginning of every new ROUND, after a period of "obscuration," the earth (as do also the other six "earths") casts off, or is supposed to cast off, her old skins as the Serpent does: therefore she is called in the Aitareya-Brahmana the Sarpa-Rajni, "the Queen of the Serpents," and "the mother of all that moves." The "Seven Skins," in the first of which she now stands, refer to the seven geological changes which accompany and correspond to the evolution of the Seven Root-Races of Humanity. -- op. cit., p. 47
It seems clear, from the foregoing, that the convulsions of nature at the beginning of each Round, as each globe reawakens in turn, are in a sense a preparation for a new life cycle, a recapitulation of that which takes place at the beginning of the Manvantara. Small and brief, because part of a smaller cycle of a globe Round within the larger cycle of the entire Manvantara, yet for that relatively short period the minerals and rocks awaken, perform their proper work, and subside into dormancy.
Turning now to earth history as recorded in geology, we find Professor John Joly of Trinity College, Dublin, in The Surface History of the Earth, page 102, saying of the convulsions of Archaean time, which preceded the life cycle of this Fourth Round:
No one who has considered these events can hesitate in ascribing to them a diastrophic magnitude far transcending all subsequent Revolutions. We appear to see before us the destruction of a past world and the birth of a new one. . . . "Nowhere, either east or west, has the original basement upon which the first sediments were laid down been discovered. They are everywhere torn to pieces by the gigantic intrusion of the Laurentian." (Adams.)
Sedimentary strata totaling seventeen miles in thickness are known to have accumulated in Pre-Cambrian times, but have been so altered, crumpled, broken and melted by repeated convulsions as to make any ordered study almost impossible.
Within this, our Fourth Round, we find the great natural cycles marked changes in the earth and its life -- which geologists call eras. Thus we have the Paleozoic era, the Mesozoic era, etc. Each of these is characterized, at its beginning, by a major elevation of land and mountain ranges, volcanic activity, and widespread cold and glaciation. Then comes a long period of erosion and invasion and flooding of continental areas by the seas. During this time, which occupies the greater part of the era, the entire world, including the polar regions, enjoys a warm if not subtropical climate. The submergences come on slowly as the period advances, spreading more and more, in an oscillating manner, as minor cycles advance and retreat, until the climax is reached. The era is brought to a close with the rapid retreat of the seas, chilling of the climate, elevation of new mountain ranges, and the formation of new ice fields thousands of feet thick, as preparation for a new era begins.
During each era a characteristic type of life springs into worldwide dominance. The Paleozoic era is noted for its coal forests, its fishes, and amphibians. The seas swarmed with life of various kinds. The Mesozoic is known as the age of reptiles. Also during this time coniferous forests covered the lands. The Cenozoic era saw the rise, the culmination, and the decline of the flowering plants and the mammalian animals. Within each era are a number of natural geologic periods which repeat the characteristics of the eras, though on a smaller scale, beginning with the lesser activities of mountain building, and glaciation, followed by invasion and flooding by the sea, and ending with new uplifts. Within these geologic periods are smaller oscillations called epochs, and within these are still smaller cycles of expansion and contraction and of advance and retreat of the seas.
H. P. Blavatsky presents in The Secret Doctrine, five esoteric axioms regarding life-waves which she says if admitted by science would solve all difficulties regarding the origin and evolution of life on this earth:
(a) The enormous antiquity (and the existence) of our planetary chain; (b) the actuality of the Seven Rounds; (c) the separation of human races (outside the purely anthropological division) into Seven distinct Root-Races, of which our present European Humanity is the fifth; (d) the antiquity of Man in this (Fourth) Round; and finally (e) that as these Races evolve from ethereality to materiality, and from the latter back again into relative physical tenuity of texture, so every living (so-called) organic species of animals with vegetation included, changes with every new Root-Race -- II, p. 697
The times of great activity beginning and closing the eras are known to science as revolutions, and much speculation has been advanced to account for them and for the cooling of the earth climate which accompanies them. The times of lesser activity beginning and ending the periods are known as disturbances.
Here we have the pattern of earth history, the very warp upon which the woof of plant and animal life is woven. For the life of a land proceeds step by step with the pulsing cycles of the land it lives upon, and it is for this life, indeed, that changes of the earth's surface take place. Thus there are times of glaciation and mountain building, these great activities occurring at cyclic intervals. And between these brief and exciting periods of activity and change are long, quiet expanses of time in which world-wide subtropical or warm climates prevail, mountains are worn down and large continental areas are slowly invaded by the seas. In general, it has been found that certain large divisions of plant and animal life have their birth and long childhood during these Garden-of-Eden conditions, and undergo rapid evolution or extinction during the following revolution.
During the lesser disturbances, at the beginning and ending of periods and epochs, there are corresponding changes in the minor divisions -- i.e., the genera and species -- of plant and animal life. The period and epoch cycles correspond with important developments and changes in the flora and fauna of the earth. These in turn rise and fall with the Root-Races of man, and when viewed as a whole, give us a glimpse of a pulsing, living earth, evolving and changing with the life -- plant, animal, and human -- living on it.
The eras, periods and revolutions of earth history are here considered as actual occurrences, irrespective of the number of years science has assigned to these different events at one time or another. In comparing the various estimates of the age of the earth offered by science, and in the esoteric figures as given by H. P. Blavatsky in The Secret Doctrine, Vol. II, page 710, it is significant that the percentage of earth history assigned to the eras and periods agrees closely, even where the figures as to the number of years do not.
Regarding the eras of ecologic history, G. de Purucker has stated that:
The main point to remember is that the different great stocks of mineral, vegetable, and animal and human lives follow each other with coincident or coordinate great changes of land and sea, and therefore also of climates.
In other words, the stocks of beings, or monads, co-operate or coordinate and thus produce the different and serial and successive patterns of what we today call geological eras, or which the biologist or zoologist and botanist would call the successive waves of plant and animal and human life.
I mean, if I can express my thought clearly, that there actually are succeeding and successive and therefore different geological eras, each one accompanied by its own monadic families in all kingdoms. -- From a private letter.
Any attempt to assign a definite number of years to the divisions of geologic history, based on present scientific knowledge, or any attempt to correlate esoteric and geologic time periods, must be considered as tentative only, and is therefore not attempted in this paper. The divisions of earth history are here considered as cyclic and serial events, rather than periods of time.
Although there is evidence that life existed in ages preceding the Paleozoic era, the first definitely known life on our globe had its beginnings in the Cambrian, or first, period of the Paleozoic. The earth had passed through a long and terrific reworking, and was ready to receive a new life-wave, that of our present Fourth Round.
The Cambrian period opened with an extreme elevation of land, general cold, and volcanic and seismic activity on a larger scale than has occurred since that time. This condition rapidly gave way to general leveling and depression of the land. With the approach of a world-wide subtropical climate, there were many evolutionary changes in plant and animal life. The period closed with the uplift known in America as the Green Mountain disturbance.
The Ordovician period which followed was characterized by a warm climate and the greatest of all submergences, during which, with the exception of low islands almost awash, the greater part of the known land was at one time or another under the sea. No climatic zones appear to have existed, and the simple animal life of the sea found tepid water throughout the surface of the globe. Fossil remains show that identical species of coral, seaweed and shellfish lived in both polar and subtropical waters. The period ended with an emergence of land during the Taconic disturbance, accompanied by a sudden cooling of the climate.
During these early times the earth and all living things on it were much more ethereal than they are now, and in this connection it is interesting to study the many ancient legends which mention the separation and condensing of the waters. In Genesis we find (Dr. de Purucker's translation):
And said Elohim (the Gods) "(let there) be-gathered-together (i.e., solidified, condensed) the waters above the heavens into one place, and (let there) be seen the dry-part (the solidified or manifested part)" The word means "dry," in opposition to humidity. Humidity means water, standing for space. It means, therefore, the collected matter of a planet to be, of a solar system to be, or of a universe to be), "and (it) came-to-be-so. And called the Gods the dry-part earth, and the solidification (gathering-together) of the waters called they seas. And saw Elohim (the Gods) that (it was) good."
On the other side of the earth the Zuni Indians expressed it thus:
With the appearance of the sun came the brightening of the spaces with light and with the brightening of the spaces the great mist-clouds were thickened together and fell, whereby was evolved water in water, the world holding sea.
The Silurian period brought another though less extensive submergence and increase in warmth, and as this period came to a close, the great Caledonian revolution occurred, ending the early part of the Paleozoic era. The Caledonian Mountain system ranged across the British Isles and Scandinavia; then, arching westward through Spitzbergen and northern Greenland to America it formed a circumpolar belt a known four thousand miles in length. From a study of present remains it is estimated that these mountains surpassed in elevation and grandeur any ranges now in existence, and from what is known of the structure of present continents we may assume that the Caledonian Range was a 'border range,' and that the mass of the associated land area probably lay to the north of the mountains. During the Caledonian revolution the world was again divided into climatic belts, and the polar seas may have been frozen over.
With the following Devonian period the climate became rapidly warmer and in the Arctic waters corals were more widespread than ever before. The first known land plants and animals then appeared in great numbers, condensing from the astral relics brought over from the Third Round, as H. P. Blavatsky says in The Secret Doctrine, Vol. II, page 712. The Devonian marks the appearance of primitive amphibians, scorpions, insects and spiders, and the first known lung-fish.
Land plants, seed ferns, calamites and scale trees appeared in abundance in the Middle Devonian, and as the period progressed Spitzbergen and other Arctic lands, under the warm, moist climate of that time, developed a luxuriant vegetation, and great beds of coal-forming vegetation were deposited. In the seas, fishes were so abundant and of such great variety that the period became known as the Age of Fishes. At the close of the Devonian period Newfoundland, New Brunswick and the Appalachian region of the United States underwent an elevation.
The Carboniferous period is divided into two parts, the first being known as the Mississippian and the second as the Pennsylvanian period. These were times of widespread continental depression. Hot, steaming lowlands and swamps filled with a luxuriant plant life covered large areas in which the immense coal-fields of today were formed. The Caledonian Mountains had been eroded almost to a plain; the end of an era was approaching; a whole order of life then at its peak was to rush down to extinction during the approaching revolution and glaciation.
The coal forests of the Carboniferous would have appeared very strange to us, for most of them were composed of seed ferns, tree ferns, cordiates, calamites and giant scale trees. Great amphibians sprawled in the swamps. Dragon-flies with a wingspread of 29 inches, and cockroaches 4 inches long, multiplied beneath the dense foliage. A few generalized reptiles existed, and these were to expand, in the following era, into numerous varieties of swimming, walking and flying creatures.
The Late Paleozoic type of plant life expanded into a great variety of large and specialized trees which died out at the close of the era. Professor Henry Fairfield Osborn calls this sudden expansion and specialization "adaptive radiation," and shows that similar or convergent adaptations in different stocks are unrelated, for each stock -- reptile, bird and mammal -- radiates or expands from a central type into forms fitted for existence in water, on land, or in the air.
Further evidence of the mild nature of Carboniferous climate lies in the fact that the coal beds of the Carboniferous period extend from near the north pole down into the temperate zone throughout North America, Alaska, Siberia, Spitzbergen, Greenland, and Europe, while recently large oil deposits have been reported from Alaska.
We would do well to study carefully the words of H. P. Blavatsky as set forth in The Secret Doctrine regarding the continents, for remnants or shields of various lands remain as focal points -- sishtas, if you like -- from age to age. These are built into new lands, for a new race, when the hour strikes.
A typical continent consists, so the geologists tell us, of two bordering ranges of mountains, with a broad, more or less level expanse of land between. This central plain submerges at times of depression, while the borderland ranges remain as partly submersed islands, or are joined to other lands rising from the shallow seas. In America, for example, more than once the Gulf of Mexico has extended, as a great inland sea, northward to the Arctic Ocean. In The Secret Doctrine H. P. Blavatsky herself says:
We believe in the seven "continents," four of which have already lived their day, the fifth still exists, and two are to appear in the future. We believe that each of these is not strictly a continent in the modern sense of the word, but that each name, from Jambu down to Pushkara, refers to the geographical names given (i) to the dry lands covering the face of the whole earth during the period of a Root-Race, in general; and (ii) to what remained of these after a geological (race) Pralaya -- as "Jambu [India]," for instance; and (iii) to those localities which will enter, after the future cataclysms, into the formation of new universal "continents," peninsulas, or dwipas -- each continent being, in one sense, a greater or smaller region of dry land surrounded with water. Thus, that whatever "jumble" the nomenclature of these may represent to the profane, there is none, in fact, to him who has the key. -- II, 404-5
So, in reading a statement regarding the sacred continents, we must know in which sense it is to be understood. It may be that in each continent there is a portion which never sinks, but remains, to be built into new patterns of land areas.
Large areas of Pre-Cambrian land remained above water throughout the Cambrian period, to be to a great extent submerged during the great flood of the Ordovician, yet certain shields (as in Canada, India and Australia) have remained to this day, and have formed in turn parts of Lemuria, Atlantis, and our own fifth continent, the latter considered as comprising all the lands above water today.
We must keep in mind always that only a part of the earth's unsubmerged surface has been studied, and that little or nothing is known of those immense areas of Atlantis and Lemuria now beneath the ocean. For this and for other reasons, H. P. B. makes it clear that the esoteric philosophy divided only the life periods on the globe, and leaves the classification of the geological periods to Western science, and it is this fact that makes it so difficult to fit the esoteric classification to the eras and periods of geology.
With the Permian period everything was changed. The Appalachian revolution of this period raised the Appalachian Mountains of the eastern United States to a total height of five miles, which, discounting progressive erosion, was probably higher than any existing peaks in North America today. In many places large areas of land emerged and other areas sank beneath the seas. At the same time the Ural Mountains in Russia were folded and elevated. In the Pacific Ocean the encircling "ring of fire" now began to appear, with extensive volcanic action from Alaska to Mexico. In the south the hypothetical Gondwana Land (the scientific version of the third continent, Lemuria) arose. Remnants of this ancient land mass are thought to exist today in Australia, India, South America, southern Africa and Antarctica.
With the Permian also came one of the greatest periods of glaciation of which we have any knowledge. Antarctica, southern Africa, Australia, and much of South America were covered with ice. The only evidence of Permian glaciation so far discovered in North America is a small deposit near Boston. It is believed by some geologists that the chill of approaching glacial winter moved from the south until the Arctic regions were finally overcome, although no satisfactory explanation has been made as to why this should be true.
By the close of the Permian period the lush growth of the coal forests had been extinguished, for but few species were able to adapt themselves to the rapid and extreme change in climate. Definitely, the end of an era had come, and as one life-wave declined, another, with new and higher forms of life, began to make its appearance. This sudden destruction of old forms of life, and the almost explosive expansion and distribution of new forms which occur at the beginning of each era is something for which modern science has no satisfactory explanation. Attempts have been made to find missing links between the various stocks of plant life, as well as of animal life, but without success. For example, the seed fern has been considered (and still is by many) as a link between the fern and the flowering plant. Yet the seed fern appeared ages before the true ferns, and is believed to represent the culmination of a former life cycle.
The Mesozoic era, opening with the Triassic period, ushered in the beginnings of a new plant and animal life, that of the Third Continent. Repeating the history of previous periods, the climate became rapidly warmer. For, extensive as Permian glaciation was, no glacial deposits have yet been found in Triassic rocks. In the sea, corals reestablished themselves as far north as Alaska. (On the Pacific coast at the present time corals will not grow north of the twenty-fourth degree of latitude, as at Magdalena Bay, Lower California.) The age of swimming, walking and flying reptiles developed in a great rush of new forms. Eighteen divisions of reptilian stock so expanded and specialized as to dominate the waters, the earth and the air throughout the Mesozoic era. Of these eighteen known divisions of reptilian life, only five remnants exist today. These are the orders which include the existing turtles, lizards, snakes and crocodiles, and also the tuateras of New Zealand, primitive reptiles possessing an active third eye. The great host of dinosaurs, ichthyosaurs, pterodactyls, and their kin, perished with the close of the era. The plant life of the Mesozoic is represented by the coniferous trees -- the pines, firs, cedars, etc., of today. The story is not complete, however, for there are two long gaps in the Mesozoic record during which nothing is known of the life on the continents.
At the close of the Jurassic, and separating it from the Cretaceous period, there occurred a minor period revolution, with an elevation of land accompanied by glaciation and lowering of temperature, including freezing of the Arctic lands. In The Secret Doctrine, H. P. B. apparently mentions this revolution in connection with the early Third Root-Race:
. . . it began in those northern regions, which have just been described a few pages back as including Behring's Straits, and what there then was of dry land in Central Asia, when the climate was semi-tropical even in the Arctic regions and most adapted to the primitive wants of nascent physical man. That region, however, has been more than once frigid and tropical in turn since the appearance of man. The commentary tells us that the Third Race was only about the middle point of its development when:
"The axle of the Wheel tilted. The Sun and Moon shone no longer overthe heads of that portion of the SWEAT BORN; people knew snow, ice and frost, and men, plants and animals were dwarfed in their growth." -- II, 329
From the study of geology we know that there was a sudden cooling of the earth at the close of the Jurassic, at which time the Sierra Nevada mountains were first raised.
With the opening of the Cretaceous period, the entire world, including the polar regions, again became warm. A new order of life -- plant, animal, and human -- developed, that of the Fourth, or Atlantean, Race, with its attendant placental mammals, and flowering trees and shrubs. The era closed with the sudden cold of the Laramide Revolution, which brought about the extinction of most of the reptilian life of the Mesozoic.
We have seen in reviewing earth history that periods of glaciation, mountain building and great earth activity occur at cyclic intervals; that between these brief periods of activity are long periods of subtropical climate accompanied by progressive invasion and flooding by the seas; that plant and animal types have their origin and long childhood during these times of continual spring and undergo rapid evolution and extinction of many species during the revolutions.
The era revolutions, and the period disturbances to a lesser extent, serve the same purpose as the greater revolutions at the close of a Round. With the usually rapid retreat of each ice age there comes a new period of mild climate. The polar regions are no longer frozen. A new order of life bursts forth in a widespread rush of energy and vitality, the Arctic once more takes on the appearance of a botanical garden, and a new Golden Age begins. All this may be learned from fossil evidence as recorded in the rocks. That which may be added by a study of The Secret Doctrine is the information on the Root-Races and Sub-Races and Sacred Continents, for the geologic record contained in the rocks and strata of our present lands is merely fragmentary.
The appearance of ice ages with alternating times of subtropical climate has never been satisfactorily accounted for by science, but the general conclusion among the leading scientists of today is that these changes are in some way due to change in solar radiation. H. P. B. mentions the inversion of the poles as a cause of many disturbances. She also says that at present the poles are slowly approaching the perpendicular, a position that will bring continual day again to the polar regions.
During the Cretaceous period the northern part of Greenland must have resembled a subtropical jungle, for at that time over three hundred species of trees and shrubs, which are now confined to warm climates, flourished there. Of these, the fig, camphor, magnolia, eucalyptus, breadfruit, persimmon, ginkgo, and holly are typical examples.
It was at the close of the Cretaceous that the great area of land (a portion of Lemuria) named Gondwana Land by Suess broke up as a continent and disappeared. There is geological evidence that this land extended from South America to Africa, reaching India and Australia and the South Pacific islands. At the same time, Peninsular India received a mile-deep covering of basalt over an area of 300,000 square miles, the Andes and Rocky Mountains underwent an uplift, and the vast seas which had covered so much of America and Eurasia withdrew. These events, which took place at the time of the destruction of the Lemurian continent, left a partial record in the strata of the existing lands of today. Because of the resulting extinction of the giant reptiles of land, sea and air, of the giant ammonites of the sea and many other forms of life, the close of the Cretaceous period is often spoken of as "the time of the great dying."
At the opening of Cenozoic times the earth activity and low temperature of the Laramide Revolution ceased, and the Eocene period rapidly became warm. Most of the old forms of life had disappeared and a new and abundant flora and fauna spread over the earth. The flowering plants and the mammalian animals, many of which originated in the far north in Cretaceous times, here divided into many types and rushed to their climax in the Miocene, which is often called the golden age of mammals and flowering plants.
From this golden age of culmination to the present day there has been a steady reduction in both plant and animal life. This cycle of earth history very closely parallels the rise, peak and breaking up of the Atlantean Race. Indeed, a study of earth history leads one to believe that the lesser lives are linked, step by step, cycle by cycle, with the races of man. How can it be otherwise? And since with each race of man there evolves some particular types of vegetation, we may associate the carboniferous forests with the Second Race, the coniferous forests with the Third Race, the flowering trees and shrubs with the Fourth Race, and the annual plants with the Fifth Race.
The Eocene, Oligocene and early Miocene periods are thought to have had a world climate similar to that of southern Florida today. With the middle Miocene came a continental depression which caused the submergence of the greater part of Atlantis and a gradual cooling of the climate of the entire globe. During the rapidly increasing cold of the following period, the Pliocene, many plants which had been perennial became annuals in order to survive the winter in the form of seeds.
The rapidly changing conditions of the Eocene produced a development and specialization of mammals so rapid as to be termed by Dr. Snyder as "almost explosive." There were many types of which we know little today, only certain kinds having survived. The creodonts, ancestors of our carnivorous animals, consisted of six families, of which only one survived, and this divided into the cat-like and dog-like groups of today. The cat-like group includes not only the lion, leopard, tiger, lynx and cat, but also the civets, mongooses and hyenas. Under the dog-like group we find the dogs, wolves, coyotes, foxes, jackals, and also the bears, weasels, otters, badgers, seals, sea lions and walruses.
Our vegetation, likewise, consists of slowly declining streams of life from the Paleozoic, Mesozoic and Cenozoic eras. In many cases, once world-dominant families are now represented by a single genus, even by a single species.
The cooling climate of the Pliocene culminated in the Pleistocene ice age.
Five great continental glaciers are recognized as having existed in the northern hemisphere. These are the Cordilleran, the Keewatin, the Labradorean, the Greenland, and the European. Investigation has shown that these ice masses made four or five great advances separated by interglacial times as warm as our own, or warmer.
These ice sheets had five centers of origin; and while formed, in chronological order from west to east, are thought by many to have overlapped, so that the last stage of the first, the middle stage of the second and the first stage of the third were contemporaneous. Geologists estimate the entire time occupied by the last great ice age as some five million years, a short period in geological time, but a very important one in its effect upon the life of the earth.
Among the mysteries of the ice age is the fact that many of the continental ice sheets originated not in the Arctic, as at first supposed, but between 50' and 60' north latitude, and extended northward as well as southward.
The Cordilleran glacial system began in the table-lands of British Columbia and the Yukon, starting as a number of mountain glaciers during Pliocene and expanding to cover an area of some 350,000 square miles, with ice of a maximum thickness of 5500 feet. At the same time, mountain glaciers developed southward as far as what is now California, including the San Gabriel range.
Next, the Keewatin ice sheet accumulated west of Hudson's Bay, at an elevation of 1000 to 5000 feet, and spread in all directions, reaching the Rocky Mountains on the west, the Arctic Ocean on the north, the middle of Hudson's Bay on the east, and southward far into Montana, North Dakota, Minnesota and through Iowa into Kansas and Missouri. This ice sheet covered an area of 1,500,000 square miles, with a maximum thickness of 10,000 feet near its center.
Then the Labradorean ice sheet developed, centering in northern Quebec, east of James Bay. It covered 2,000,000 square miles, and extended from the Arctic to the Ohio River and east to the Atlantic. The thickness of this glacier reached 12,000 feet.
The Greenland glacier was the next to form and the last to retreat. It is the only continental glacier existing today in the northern hemisphere. Its present area is about 700,000 square miles, with a depth of 7,000 to 8,000 feet near its center.
In Europe, an ice cap with its center in the region of the Gulf of Bothnia extended northward into the Arctic Ocean, westward across the North Sea and the British Isles, southward into Germany and eastward across Russia. Its greatest expanse was some 2,000,000 square miles, with a maximum depth of 12,000 feet.
It is interesting to note that at the present time the areas about which these great glaciers centered are rising at the rate of about three meters per century.
There remains the ice sheet in Antarctica to mention. This is the largest one of all, covering 5,000,000 square miles. At present it is slowly shrinking, due to water starvation.
What effect did the ice age have on plant life? First, beginning in the Pliocene period, many perennials became annuals, preserving their life during the cold of winter encased in seeds, and many trees became bushes. Second, great migrations of plants and animals took place. The colonies of pines, firs and cedars in our southern mountains today are descendants of individuals which formed parts of great forests during the general cooling of climate caused by one
or more of the glacial advances.
The following is a very intuitive description of earth-cycles. It is from Surface History of the Earth, by John Jo1y, SC. D., F. R. S., Fellow of Trinity College, Dublin:
The surface history of the earth has been by no means uniform and monotonous. Great physical changes have been repeated at intervals. It would appear as if six great cycles of world-transforming events are recognizable during the course of geological history. In each of these cycles the succession of events has been the same. The continents sink relatively to the ocean. The waters flow in over the lower levels and vast areas become covered by the transgressional seas. These seas persist over very long periods -- fluctuate in area -- advance and retreat, often many times -- but always still advancing until at length a time is reached when retreat overtakes advance and little by little the land rises again. And now a strange climax is attained. Just where the seas have been most enduring, mountains begin to arise. First it seems as if lateral forces were at work. For the rising deposits -- the age-long sedimentary accumulations of the geosynclines -- come up crushed, folded, and even over-thrust for many miles. These are destined to form the mountain ranges of the ensuing era. A last great vertical uplift, long after the first deformation of the sediments, raises these new-born mountain ranges high above the continental level: an uplift which may amount to many thousands of feet. -- page 79
A very fascinating study is that of the formation and behavior of glacial ice. It opens a field of inquiry which by many has been hitherto unsuspected.
Beginning with the study of the formation of snowflakes, we learn that a cloud is composed of multitudes of minute particles of moisture condensed about a nucleus of dust. Such dust-nuclei have origin in the dust born of burned-out meteorites, in the dust ejected from volcanoes, in smoke particles, or in infinitely small salt crystals drawn up from the sea into the earth's atmosphere.
In the higher strata of the troposphere, water vapor freezes directly around these dust particles, forming small triangular or hexagonal ice crystals. These crystals descend within the storm cloud, serving as nuclei around which snowflakes are formed. The central hexagonal plate of ice at the center of a snowflake is formed in the colder strata of the atmosphere, while the rays are added as the snowflake descends, through several warmer and more humid levels, on its way to earth. Thus when the snowflake falls to the ground it bears a record of the characteristics of each layer of air through which it has fallen, for each of the strata has contributed to its formation.
In the formation of glacial ice, when snowflakes reach the earth they lose their plumes and are recrystallized into hexagonal granules about one-tenth of a millimeter in diameter. During their first summer in an Arctic or Alpine region, these granules grow by means of the process of melting and recrystallization, the larger ones absorbing the smaller ones. At the age of one year, the snow has become a compact, granular mass, in character midway between snow and ice, and is called neve or firn.
Geologically speaking, water is a mineral and ice a crystalline rock in one of several stages of formation. The process of melting and recrystallization in ice or snow is similar to that which takes place in the heating and tempering of metals. This melting and breaking up of a crystal, whether of metal or of ice, and its recrystallization, may be looked upon as an analogous or identical process within the two substances.
Each year brings more snow and pressure upon the first layer of the young and growing glacier, which becomes more and more compact. The granules continue to increase, both in size and in number, and, when about one hundred feet of snow have been accumulated, each ice crystal of this first layer, or stratum, has attained a diameter of several millimeters, the axes of each of the crystals being arranged at right angles to the direction of future movement. Now the glacier begins to move, or flow, while the yearly addition of snow feeds and replaces the ice which has descended from the higher altitudes.
From our study thus far made, we may understand the nature and power of one of the great continental ice masses, which is perhaps ten thousand feet thick, while the older crystals composing it are sometimes the size of melons.
Although in the later stages of glaciation the ice may appear clear and compact, nevertheless the granular structure is everywhere present in it, and as Tyndall has shown, melting ice, if viewed in a certain light, reveals its original snowflake or crystalline structure.
Science offers a number of theories to explain the ice ages and the climatic changes in geologic history. There is the Wegener theory that, as a result of the drifting of continental areas southward, and then northward, there came the periods of warmth in what are now the Arctic regions. This explanation, now largely discredited, fails to account for the warm inter-glacial periods and the uniformity of world climate during the greater part of the earth's history.
According to John Joly, periodical increases of radioactivity melt the basaltic under-strata of the earth's crust and cause the rise, fall, and shifting of land masses. The existence of the basaltic strata or of extensive radioactivity at great depths is yet to be proved. It seems likely that conditions exist within the earth of which we know little. Recent technique in treating metals under nitrogen and carbon dioxide atmospheres show how important these conditions are in the behavior of metals.
Others, following Croll, suppose that an extreme eccentricity of the earth's orbit may have brought about glacial conditions, but this theory also presents too many objections when closely examined. One objection, pointed out by W. B. Wright, is that this theory would place the last ice age about 80,000 years ago, whereas the last ice age is known to have ended some 25,000 years ago. The last ice age also comprised a number of glacial advances, with interglacial periods as warm as or warmer than the climate of the earth at present.
The solar variation-theory upon first examination appears to be the soundest, but a decrease in the heat received from the sun actually results in a decrease in atmospheric circulation and hence in a lessened, instead of increased, precipitation.
The current explanations of Milanhovitch, based on periodical cycles due to the obliquity of the ecliptic, are accepted by many, but these, too, present certain difficulties.
In The Secret Doctrine, H. P. Blavatsky makes many references to inversions and tipping of the earth's axis, and associates them with the rise and fall of continents and with the ice ages. Note the following:
Thus, since Vaivasvata Manu's Humanity appeared on this Earth, there have already been four such axial disturbances; when the old continents -- save the first one -- were sucked in by the oceans, other lands appeared, and huge mountain chains arose where there had been none before. The face of the Globe was completely changed each time; the survival of the fittest nations and races was secured through timely help; and the unfit ones -- the failures -- were disposed of by being swept off the earth. Such sorting and shifting does not happen between sunset and sunrise, as one may think, but requires several thousands of years before the new house is set in order.
The Sub-Races are subject to the same cleansing process, as also the side-branchlets (the family-Races). -- II, p. 330
William Quan Judge says, in The Ocean of Theosophy, Chapter 14:
Ice cataclysms come on not only from the sudden alteration of the poles but also from lowered temperature due to the alteration of the warm fluid currents in the sea and the hot magnetic currents in the earth, the first being known to science, the latter not.
In The Mahatma Letters the Master K. H. makes a number of very important statements regarding the cause of ice ages. He says:
Earth's magnetic attraction of meteoric dust, and the direct influence of the latter upon the sudden changes of temperature especially in the matter of heat and cold, is not a settled question to the present day, I believe. . . . I wonder how Science has not hitherto understood that every atmospheric change and disturbance was due to the combined magnetism of the two great masses between which our atmosphere is compressed! -- p. 161
Science makes too much and too little at the same time of "solar energy" and even of the Sun itself; and the Sun has nothing whatever to do with rain and very little with heat. I was under the impression that science was aware that the glacial periods as well as those periods when temperature is "like that of the carboniferous age" -- are due to the decrease and increase or rather to the expansion of our atmosphere, which expansion is itself due to the same meteoric presence? At any rate, we all know that the heat that the earth receives by radiation from the Sun is at the utmost one third if not less of the amount received by her directly from the meteors. -- p. 162
It is known to scientists that the atmosphere or vapor sphere becomes steadily colder up to a height of about seven miles, where a temperature of at least minus eighty degrees Fahrenheit exists. This zone of winds and clouds is known as the troposphere -- from trop, signifying to turn or overturn, with reference to the continual changes of the air masses of our atmosphere by storms.
Above the troposphere lies the ozonosphere, or first layer of the stratosphere, where storms and clouds cease to be and the air gradually becomes less cold. At an elevation of about twenty miles, a thick layer of ozone absorbs, and is highly heated by, the ultraviolet rays of the sun. Ozone, a triatomic form of oxygen, is said to absorb heat more readily than any other gas. If it were not for the protection of the ozonosphere, the ultraviolet rays released from the sun would so burn the skin and blind the eyes as to make life on earth almost unbearable.
Still higher, at an elevation of 100 to 200 miles, is the Appleton layer, in which an intense ionization takes place. This is also a belt of great heat.
All these zones vary in elevation above the earth, being lower at the poles than at the equator, lower in the winter than in the summer, and lower at night than in the daytime.
The exploration of the earth's higher frontiers by radio wave, balloon and rocket is one of the foremost fields of research at the present time, as both radio and aviation are so largely dependent upon the information thus obtained. Many aerologists are coming to believe that surface conditions are in large degree made in the stratosphere, or, in other words, are subject to 'upstairs control.'
In a recent book by William Holmes Wenstrom, Weather and the Ocean of Air, we find that "the surface high represents not the greatest amount of cold air aloft, but the greatest convergence of air aloft."
Our atmosphere is compressed between the earth and the heated zones of the stratosphere, and the expansion and compression of this air is accompanied by highs and lows, and by weather changes upon the earth's surface. The temperature zones in the lower ranges of the atmosphere are of great importance in the distribution of life, and any change in the troposphere must have an immediate effect on the climate and life on the surface of the earth.
At present, we find our world divided into seven life zones, as follows: Three warm zones, namely, (1) the tropical, (2) the lower austral (also known as the lower Sonoran), (3) the upper austral, (also known as the upper Sonoran), (4) an intermediate, transition zone; and three cool, or boreal, zones, namely, (5) the Canadian, (6) the Hudsonian, and (7) the Arctic Alpine.
We may imagine our earth as being surrounded by successive layers of these zones, arranged like the layers of an onion, except that certain zonal layers are thick at the earth's equator, thinning out and finally disappearing as they recede northward and southward, which condition prevails in the atmosphere itself. The zonal layer at the equator is that of the tropical zone. The next zone is the lower austral. This, like the following zone, the upper austral, overlies the tropical and extends far beyond it, both to the north and to the south. It will be observed that the layers are not uniformly deep in any locality. The dominant zone for any area is the zone greatest in depth and influence.
In general, for each thousand feet we rise in climbing a mountain, we find an average annual decrease of four degrees Fahrenheit in temperature, with a corresponding change in plant and animal life, which consists of types fitted to the colder environment. In short, we can find Canadian types of life by going to Canada, or by climbing a high mountain.
In the north the three dominant higher life zones expand over a considerable range, the lower zones, wherever present, being greatly constricted. In California, these same upper zones, when present on our high mountains, are greatly compressed. Instead of occupying thousands of feet in altitudinal depth, they may occupy a mere few hundred feet. On the Pacific Coast, the timber line rises from a short distance above sea level in Alaska to about 5000 feet in the mountains of Oregon, 10,000 feet in those of Southern California, and still higher in the mountains of Mexico. A similar line extending through the Rocky Mountains, or along the Atlantic Coast, will show corresponding timberline levels at somewhat different latitudes, due to continental climatic conditions and the influence of ocean currents.
During the long, warm periods between ice ages, these divisions into zones either did not exist or were obscure. Life was cosmopolitan, and the seasons of the year were much alike. As the revolutions and glacial periods developed, the whole world was affected, dividing the globe into climatic or life zones from tropics to poles and from base to summit of the mountain ranges, while the seasons of the year became strongly contrasted, causing trees to develop rings of summer and winter wood. Any expansion or compression of the belt of life zones may, in the first case, lift the belt of cold high above a particular mountain, or, in the second case, lower it, bringing about sudden glacial conditions.
For a number of years the Geophysical Union, a branch of the U. S. Geological Survey, through a large number of trained assistants, has been making surveys and collecting data concerning the glaciers of the Northern Hemisphere. Most of the findings thus obtained are, to say the least, quite startling. Take, for instance, those relating to the Nisqually Glacier of Mount Rainier. This glacier has retreated at an average rate of severity feet annually for the last twenty-two years, but the reduction in its mass is, correspondingly, much greater than its retreat. In fact during the years 1910 to 1931, the losses in its snow area averaged about 500 acre-feet per year. From 1931 to 1936 the losses were about 750 acre-feet per year, and from 1936 to 1940 they totaled 3400 acre-feet per year. The losses during the thirty years under observation amounted to 27,850 acre-feet.
In the Cascade Mountains, in the Sierra Nevadas, in Glacier National Park, in Alaska, Iceland and Greenland, and elsewhere, the record indicates constant glacial retreat.
Muir Glacier, in Alaska, has retreated thirteen and one-half miles since its discovery in about the year 1885. On Mount Rainier, Paradise Glacier has retreated so far that it is little more than the southern flank of the parent mass from which it branches. The famous ice cave has vanished. Sholes Glacier of Mount McLaughlin, in southern Oregon, has completely vanished, being the third glacier in the southern Cascade Range to disappear in the last few years. A number of other glaciers are about to become extinct.
Dr. Gutenberg, of the California Institute of Technology, reports that in many places the level of the oceans has risen at the average rate of four and one-half inches per century during recent decades. He believes this to be due to an uplift of the bottom of Hudson's Bay and other northern regions, to the melting of glaciers and polar ice caps, and to the rising of ocean bottoms in certain places. The sea level at San Diego is shown to be rising at the rate of seventeen centimeters per century, Los Angeles fourteen, San Francisco twelve, Seattle four, while on the Atlantic Coast the sea level south of Boston is said to be rising at an even faster rate.
On the other hand Lynn Canal Alaska and the Hudson Bay region are found to be rising above the level of the sea, at the rate of two, and three meters respectively per century.
In brief, the Arctic and Antarctic regions are rising rapidly throughout the world, while the middle temperate and tropical zones of the earth are, in general, sinking. This is believed to be partly due to the release of ice pressure in the northern regions, permitting the lands to rise to their normal position.
The Pleistocene period is supposed to have ended some 25,000 years ago, with a rapid retreat of the ice. Some 8,000 years ago the world became much warmer than it is today -- so warm, indeed, that the polar regions were free of ice, mountain glaciers had retreated to an altitude of a thousand feet (the larger number vanishing entirely), and such plants as grapes grew in Lapland.
Between 4000 and 5000 years ago a Little Ice Age returned, freezing the Arctic seas, renewing the mountain glaciers; and coldness once more took possession of the polar lands.* All but a few of the largest mountain glaciers of the world are believed to date from the beginning of this Little Ice Age; that is to say, from the commencement of Kali-Yuga.
*[For a full discussion of the cause of ice ages see Physics of the Earth, Series 1940, by F. E. Matthes; Physics of the Air, by W. J. Humphreys; and Hypotheses on the Development of the Earth's Crust and Their Implications, by Beno Gutenberg, in Internal Constitutions of the Earth, 1939.]
In The Secret Doctrine, H. P. B. states that one precessional cycle ago the inclination of the sun was 27 1/2 degrees (it is now 23 1/2 degrees) and that as this movement of inclination continues, the world temperatures and seasons will, in time, be very greatly affected.
It seems possible, in view of what is already known of geological processes and of the earth's life-waves, that when the new Race appears, our planet will once more enjoy a uniformly mild climate, and be ready to receive these more highly evolved human inhabitants.
The peaks represent times of continental uplift, mountain building, and glaciation, with worldwide lowering of temperature. The valleys represent times of continental depression, flooding by the sea, disappearance of glaciers, with worldwide warm or even subtropical climate.
The times of greatest activity delimit the eras, and are known as revolutions; the times of lesser activity are known as disturbances, and delimit the periods.
Both revolution and disturbances are named for the locality of some outstanding and well-known uplift, although the disturbance may -- and usually does -- produce mountains in other parts of the world as well.
The peaks indicate increased rainfall, lowered temperature, and advance of glacial ice. The valleys indicate times of drought and recession of glacial ice. During these dry periods great wars and migrations of peoples have occurred. The warm climate shown as existing before 2000 BC is known as the Climatic Optimum.
Berry, E. W., Tree Ancestors, Williams and Wilkins, Baltimore, 1923. An interesting geological history of trees.
Blair, T. A., Weather Elements, Prentice-Hall, Inc., New York, 1942.
Blavatsky, H. P., The Secret Doctrine, Theosophical University Press, Covina, California, 1888.
Chaney, R. W., A Pleistocene Flora from Santa Cruz Island, Carnegie Institute of Washington, D. C., No. 415, pp. 1-24.
Clements, F. E., and Shelford, V., Bio-Ecology, John Wiley & Sons, New York, 1939. A study of plant, animal, and human life, and their interactions.
Crickmay, C. H., Jurassic History of North America, Proceedings of the American Philosophical Society, Vol. 70, 1931.
Dayton, C. M., Sparks, Lightning, Cosmic Rays, The Macmillan Company, New York, 1939.
Grey, G. W., The Advancing Front of Science, Whittlesey House, London, 1939. Has an interesting chapter on the stratosphere.
Gutenberg, Beno, Changes in Sea Level, Postglacial Uplift, and Mobility of the Earth's Interior, Bulletin, Geological Society of America, Vol. 52, pp. 721 et seq. Gives figures on rise and fall of land throughout the world.
Gutenberg, Beno, Velocity of Sound Waves and the Temperatures in the Stratosphere in Southern California, Bulletin, American Meteorological Society, May, 1939.
Hegner, R. W., College Zoology, The Macmillan Company, New York, 1937. Gives a comprehensive review of the animal kingdom, with references to fossil forms.
Joly, John, Surface History of the Earth, Clarendon Press, Oxford, England, 1930. Contains much valuable information not to be found elsewhere regarding the geological revolutions.
Mahatma Letters to A. P. Sinnett, The,Theosophical University Press, Covina, California. (Published by Rider & Co., London, 1933.) Contains many valuable hints on scientific problems.
Matthes, F. E., Physics of the Earth, Vol. IX, Chapter V, "Glaciers," McGraw-Hill Book Company, New York 1942. The best work available on the subject.
Matthes, F. E., Report of Committee on Glaciers, American Geophysical Union Transactions, 1939-1940.
Merriam, C. H., Life Zones and Crop Zones of the United States, United States Department of Agriculture, 1893. Also subsequent reports of the U. S. Biological Surveys of the different states.
Osborn, H. F., The Age of Mammals in Europe, Asia and North America, The Macmillan Company, New York, 1910. Valuable for its treatment of evolution and adaptive radiation.
Osborn, H. F., The Origin and Evolution of Life, Charles Scribner's Sons, New York, 1917.
Schubert & Dunbar, Text Book of Geology, John Wiley & Sons, New York, 1933, 1941. Gives summary of climatic conditions for each period.
Snider, L. C., Earth History, The Century Company, New York, I932. Contains chapters on the geological history and evolution of plant and animal life.
Stocking, H. E., Up from the Depths, "Natural History," New York, December 1942 issue. A popular and informative article on the atmosphere.
Tyndall, John, The Forms of Water, J. A. Hill & Company, New York, 1904. Weaver, J. E., and Clements F. E., Plant Ecology, McGraw-Hill Book Company, New York, 1938.
Wenstrom, W. H., Weather, Houghton Mifflin Company, Boston, 1942. This book interprets the science of the air in a way that the ordinary man can understand.