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A. Four hooks showing the development of knowledge as to Historical PulsO' 

tions of Clitnaie, 

The Pnlse of Asia. Boston, 1907. 

Explorations in Turkestan. Expedition of 1903. Washington, 1905. 

Palestine and Its Transformation. Boston, 1911. 

The Climatic Factor, as lUostrated in Arid America. Washington, 1914. 

B. Two books Uhtstrating the effect of climate on man. 

Civilization and Climate. New Haven, 1915. 
World Power and Evolution. New Haven, 1919. 

C. Four hooks illustrating the general principles of Geography, 

Asia: A Geography Beader. Chicago, 1912. 

The Bed Man's Continent New Haven, 1919. 

Principles of Human Geography (with 8. W. Gushing). New York, 1920. 

Business Geography (with ¥. E. Williams). New York, 1922. 

D. A companion to the present volume. 

Earth and Sun: An Hypothesis of Weather and Sunspots. New Haven. 
In press. 


(Geography, Geology and Biology of Southern Dakota. Vermilion, 1912. 

The Biology of Northwestern South Dakota. Vermilion, 1914. 

The Geography of South Dakota. Vermilion, 1918. 

Handbook of the Geology of Indiana (with others). Indianapolis, 1922. 

Hurricanes of Australia and the South Pacific. Melbourne, 1922. 





Beaeareh Aasoeiate in G«ographj' in Tale Univeraity 



Associate Professor of Qeologj 
in Indiana TJniTersitj 






\ V ' " i^v ^ ' y '- ^ ^ ' "■ ■ . 

S S<^7^. g^.S" 




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\ • 



Published 1922. 



The present volume is the fifth work published by the Tale 
University Press on the Theodore L. Glasgow Memorial Publica- 
tion Fund. This foundation was established September 17, 1918, 
by an anon3rmous gift to Yale University in memory of Flight 
Sub-Lieutenant Theodore L. Glasgow, R.N. He was bom in 
Montreal, Canada, and was educated at the University of Toronto 
Schools and at the Royal Military College, Kingston. In August, 
1916, he entered the Royal Naval Air Service and in July, 1917, 
went to France with the Tenth Squadron attached to the Twenty- 
second Wing of the Royal Flying Corps. A month later, August 
19, 1917, he was killed in action on the Ypres front. 








Thebb is a toy, which I have heard, and I would not have 
it given over, hut waited upon a little. They say it is ob- 
served in the Low Countries (I know not in what part), 
that every five and thirty years the same kind and suit 
of years and weathers comes about again; as great frosts, 
great wet, great droughts, warm winters, summers unth 
little heat, and the like, and they call it the prime; it is a 
thing I do the rather mention, because, computing back- 


wards, I have found some concurrence. 



T T"NITY is perhaps the keynote of modem science. 
I This means tmity in time, for the present is but 

\^^ the outgrowth of the past, and the future of the 
present. It means unity of process, for there seems to be 
no sharp dividing line between organic and inorganic, 
physical and mental, mental and spiritual. And the unity 
of modem science means also a growing tendency toward 
cooperation, so that by working together scientists dis- 
cover much that would else have remained hid. 

This book illustrates the modern trend toward unity in 
all of these ways. First, it is a companion volume to 
Earth and Sun. That volume is a discussion of the causes 
of weather, but a consideration of the weather of the 
present almost inevitably leads to a study of the climate 
of the past. Hence the two books were written originally 
as one, and were only separated from considerations of 
convenience. Second, the unity of nature is so great that 
when a subject such as climatic changes is considered, it 
is almost impossible to avoid other subjects, such as the 
movements of the earth's crust. Hence this book not only 
discusses climatic changes, but considers the causes of 
earthquakes and attempts to show how climatic changes 
may be related to great geological revolutions in the 
form, location, and altitude of the lands. Thus the book 
has a direct bearing on all the main physical factors 
which have molded the evolution of organic life, includ- 
ing man. 


In the third place, this volume illustrates the unity of 
modem science because it is preeminently a cooperative 
product. Not only have the two authors shared in its 
production, but several of the Yale Faculty have also 
cooperated. From the geological standpoint, Professor 
Charles Schuchert has read the entire manuscript in its 
final form as well as parts at various stages. He has 
helped not only by criticisms, suggestioiis, and facts, but 
by paragraphs ready for the printer. In the same way 
in the domain of physics. Professor Leigh Page has re- 
peatedly taken time to assist, and either in writing or by 
word of mouth has contributed many pages. In astron- 
omy, the same cordial cooperation has come with equal 
readiness from Professor Frank Schlesinger. Professors 
Schuchert, Schlesinger, and Page have contributed so 
materially that they are almost co-authors of the volume. 
In mathematics. Professor Ernest W. Brown has been 
similarly helpful, having read and criticised the entire 
book. In certain chemical problems. Professor Harry W. 
Foote has been our main reliance. The advice and sugges- 
tions of these men have frequently prevented errors, and 
have again and again started new and profitable lines of 
thought. If we have made mistakes, it has been because 
we have not profited sufficiently by their cooperation. If 
the main hypothesis of this book proves sound, it is 
largely because it has been built up in constant consulta- 
tion with men who look at the problem from different 
points of vision. Our appreciation of their generous and 
unstinted cooperation is much deeper than would appear 
from this brief paragraph. 

Outside the Yale Faculty we have received equally 
cordial assistance. Professor T. C. Chamberlin of the Uni- 
versity of Chicago, to whom, with his permission, we take 
great pleasure in dedicating this volume, has read the 


entire proof and has made many helpful suggestions. 
We cannot speak too warmly of our appreciation not 
only of this, but of the way his work has served for years 
as an inspiration in the preliminary work of gathering 
data for this volume. Professor Harlow Shapley of Har- 
vard University has contributed materially to the chap- 
ter on the sun and its journey through space ; Professor 
Andrew E. Douglass of the University of Arizona has 
put at our disposal some of his unpublished results; 
Professors S. B. Woodworth and Reginald A. Daly, and 
Mr. Robert W. Sayles of Harvard, and Professor Henry 
F. Reid of Johns Hopkins have suggested new facts and 
sources of information; Professor E. R. Cumings of 
Indiana University has critically read the entire proof; 
conversations with Professor John P. Buwalda of the 
Umversity of CaUfornia whUe he was teaching at YaJe 
make him another real contributor; and Mr. Wayland 
Williams has contributed the interesting quotation from 
Bacon on page x of this book. Miss Edith S. Russell has 
taken great pains in preparing the manuscript and in 
suggesting many changes that make for clearness. Many 
others have also helped, but it is impossible to make due 
acknowledgment because such contributions have become 
so thoroughly a part of the mental background of the 
book that their source is no longer distinct in the minds 
of the authors. 

The division of labor between the two authors has not 
followed any set rules. Both have had a hand in all parts 
of the book. The main draft of Chapters VII, VIII, IX, 
XI, and Xin was written by the junior author ; his con- 
tributions are also especially numerous in Chapters X 
and XV; the rest of the book was written originally by 
tiie senior author. 



L The Uniformity of Climate 1 

n. The VariabiUty of Climate 16 

IIL Hypotheses of Climatic Change .... 33 

rv. The Solar Cyclonic Hypothesis .... 51 

V. The CUmate of History 64 

VI. The Climatic Stress of the Fourteenth Cen- 
tury 98 

VII. Glaciation According to the Solar Cyclonic 

Hypothesis 110 

VTH. Some Problems of Glacial Periods . . . 130 

IX. The Origin of Loess 155 

X. Causes of Mild Geological Climates . . . 166 
XL Terrestrial Causes of Climatic Changes . . 188 
Xn. Post-Glacial Crustal Movements and Cli- 
matic Changes 215 

XJH. The Changing Composition of Oceans and 

Atmosphere 223 

XIV. The Effect of Other Bodies on the Sun . . 242 

XV. The Sun's Journey through Space . . . 264 

XVI. The Earth's Crust and the Sun .... 285 



Fig. 1. Climatic changes and mountain building 25 

Fig. 2. Storminess at sunspot maxima vs. 

minima 54 

Fig. 3. Relative rainfall at times of increasing 

and decreasing sunspots . . . . 58, 59 
Fig. 4. Changes of climate in California and in 

western and central Asia .... 75 

Fig. 5. Changes in California climate for 2000 

years, as measured by growth of Se- 
quoia trees 77 

Fig. 6. Distribution of Pleistocene ice sheets . 123 
Fig. 7. Permian geography and glaciation . . 145 
¥ig. 8. Effect of diminution of storms on move- 
ment of water 175 

Fig. 9. Cretaceous Paleogeography .... 201 
Fig. 10. Climatic changes of 140,000 years as in- 
ferred from the stars* 279 

Fig. 11. Sunspot curve showing cycles, 1750 to 

1920 283 

Fig. 12. Seasonal distribution of earthquakes . 299 

Fig. 13. Wandering of the pole from 1890 to 1898 303 



1. The Geological Time Table 5 

2. Types of Climatic Sequence 16 

3. Correlation Coefficients between Bainfall 

and Growth of Sequoias in California . 80 

4. Correlation Coefficients between Rainfall 

Records in California and Jerusalem . 84 

5. Theoretical Probability of Stellar Ap- 

proaches 260 

6. Thirty-Eight Stars Having Largest Known 

Parallaxes 276,277 

7. Destructive Earthquakes from 1800 to 1899 

Compared with Sunspots 289 

8. Seasonal March of Earthquakes 295 

9. Deflection of Path of Pole Compared with 

Earthquakes . 305 

10. Earthquakes in 1903 to 1908 Compared with 
Departures of the Projected Curve of the 
Earth's Axis from the Eulerian Position 306 


THE role of climate in the life of today suggests its 
importance in the past and in the future. No hu- 
man being can escape from the fact that his food, 
clothing, shelter, recreation, occupation, health, and 
energy are all profoundly influenced by his climatic sur- 
roundings. A change of season brings in its train some 
alteration in practically every phase of human activity. 
Animals are influenced by climate even more than man, 
for they have not developed artificial means of protect- 
ing themselves. Even so hardy a creature as the dog 
becomes notably different with a change of climate. The 
thick-haired ** husky *' of the Eskimos has outwardly 
little in common with the small and almost hairless 
canines that grovel under foot in Mexico. Plants are even 
more sensitive than animals and men. Scarcely a single 
species can flourish permanently in regions which differ 
more than 20° C. in average yearly temperature, and for 
most the limit of successful growth is 10°.^ So far as we 
yet know every living species of plant and animal, includ- 
ing man, thrives best under definite and limited conditions 
of temperature, humidity, and sunshine, and of the com- 
position and movement of the atmosphere or water in 
which it lives. Any departure beyond the limits means 
lessened efficiency, and in the long run a lower rate of 

1 W. A. Setchell : The Temperature Interval in the Geographical Distribu- 
tion of Marine Algs&; Science^ VoL 52, 1920, p. 187. 


reproduction and a tendency toward changes in specific 
characteristics. Any great departure means suffering or 
death for the individual and destruction for the species. 

Since climate has so profound an influence on life 
today, it has presumably been equally potent at other 
times. Therefore few scientific questions are more im- 
portant than how and why the earth 's climate has varied 
in the past, and what changes it is likely to undergo in 
the future. This book sets forth what appear to be the 
chief reasons for climatic variations during historic and 
geologic times. It assumes that causes which can now be 
observed in operation, as explained in a companion 
volume entitled Earth and Sun, and in such books as 
Humphreys' Physics of the Air, should be carefully 
studied before less obvious causes are appealed to. It 
also assumes that these same causes will continue to 
operate, and are the basis of all valid predictions as to 
the weather or climate of the future. 

In our analysis of climatic variations, we may well 
begin by inquiring how the earth's climate has varied 
during geological history. Such an inquiry discloses three 
great tendencies, which to the superficial view seem con- 
tradictory. All, however, have a similar effect in provid- 
ing conditions under which organic evolution is able to 
make progress. The first tendency is toward uniformity, 
a uniformity so pronounced and of such vast duration 
as to stagger the imagination. Superposed upon this 
there seems to be a tendency toward complexity. During 
the greater part of geological history the earth 's climate 
appears to have been relatively monotonous, both from 
place to place and from season to season; but since the 
Miocene the rule has been diversity and complexity, a 
condition highly favorable to organic evolution. Finally, 
the uniformity of the vast eons of the past and the 


tendency toward complexity are broken by pulsatory 
changes, first in one direction and then in another. To 
our limited human vision some of the changes, such as 
glacial periods, seem to be waves of enormous propor- 
tions, but compared with the possibilities of the universe 
they are merely as the ripples made by a summer zephyr. 
The uniformity of the earth's climate throughout the 
vast stretches of geological time can best be realized by 
comparing the range of temperature on the earth during 
that period with the possible range as shown in the entire 
solar system. As may be seen in Table 1, the geological 
record opens with the Archeozoic era, or **Age of Uni- 
cellular Life, ' ' as it is sometimes called, for the preceding 
cosmic time has left no record that can yet be read. 
Practically no geologists now believe that the beginning 
of the Archeozoic was less than one hundred million 
years ago ; and since the discovery of the peculiar proper- 
ties of radium many of the best students do not hesitate 
to say a billion or a billion and a half.^ Even in the 
Archeozoic the rocks testify to a climate seemingly not 
greatly different from that of the average of geologic 
time. The earth's surface was then apparently cool 
enough so that it was covered with oceans and warm 
enough so that the water teemed with microscopic life. 
The air must have been charged with water vapor and 
with carbon dioxide, for otherwise there seems to be no 
possible way of explaining the formation of mudstones 
and sandstones, limestones of vast thickness, carbona- 
ceous shales, graphites, and iron ores.* Although the 
Archeozoic has yielded no generally admitted fossils, yet 
what seem to be massive algae and sponges have been 

sj. Barrell: Bhjtlims and the MeasarementB of Geologic Time; Bull. 
Geol. Soc. Am., Vol. 28, Dec., 1917, pp. 745-904. 

8 Pirason and Schuehert: Textbook of Geology, 1915, pp. 538-550. 


found in Canada. On the other hand, abundant life it 
believed to have been present in the oceans, for by nc 
other known means would it be possible to take from thi 
air the vast quantities of carbon that now form carbona 
ceous shales and graphite. 

In the next geologic era, the Proterozoic, the re- 
searches of Walcott have shown that besides the marine 
algSB there must have been many other kinds of life. The 
Proterozoic fossils thus far discovered include not onlj 
microscopic radiolarians such as still form the red ooze 
of the deepest ocean floors, but the much more signifi- 
cant tubes of annelids or worms. The presence of the 
annelids, which are relatively high in the scale of organi- 
zation, is generally taken to mean that more lowly fomai 
of animals such as coelenterates and probably even tb 
moUusca and primitive arthropods must already havi 
been evolved. That there were many kinds of marin 
invertebrates living in the later Proterozoic is indicate 
by the highly varied life and more especially the trilo 
bites found in the oldest Cambrian strata of the nex 
succeeding period. In fact the Cambrian has spongeg 
primitive corals, a great variety of brachiopods, th 
beginnings of gastropods, a wonderful array of trilobites 
and other lowly forms of arthropods. Since, under th 
postulate of evolution, the life of that time forms an ub 
broken sequence with that of the present, and since man; 
of the early forms differ only in minor details from tho 
of today, we infer that the climate then was not ve 
different from that of today. The same line of reasoni 
leads to the conclusion that even in the middle of t 
Proterozoic, when multicellular marine animals mxa 
already have been common, the climate of the earth h{ 
already for an enormous period been such that all tl 
lower types of oceanic invertebrates had already evolve 





Formative Era. Birth and growth of the earth. BeginningB of 
the atmosphere, hydrosphere, continental platforms, oceanic 
basins, and possibly of life. No known geological record. 


Archeozoic Era. Origin of simplest life. 

Proterozoio Era. Age of invertebrate origins. An early and a late 

ice age, with one or more additional ones indicated. 
Paleozoic Era. Age of primitive vertebrate dominance. 

Cambrian Period. First abundance of marine animals and domi- 
nance of trilobites. 

Ordovidan Period. First known fresh-water fishes. 

Silurian Period, First known land plants. 

Devonian Period. First known amphibians. ''Table Mountain" 
ice age. 

Mississippian Period. Bise of marine fishes (sharks) . 

Pennsylvanian Period, Bise of insects and first period of marked 
coal accumulation. 

Permian Period. Bise of reptiles. Another great ice age. 
Mssozoic Era. Age of reptile dominance. 

Triaseic Period. Bise of dinosaurs. The period closes with a cool 

Jurassic Period. Bise of birds and flying reptiles. 

Comanchean Period. Bise of flowering plants and higher insects. 

Cretaceous Period. Bise of archaic or primitive mammalia. 
CsNOZOic Era. Age of mammal dominance. 

Early Cenoeoio or Eocene and Oligocene time. Bise of higher 
mammals. Glaciers in early Eocene of the Laramide Moun- 

Late Cenoeoic or Miocene and Pliocene time. Transformation of 
ape-like animals into man. 

Glacial or Pleistocene time. Last great ice age. 


PsTCHOZOic Era. Age of man or age of reason. Includes the 
present or ' ' Becent time, ' ' estimated to be probably less than 
30,000 years. 

4 From Charles Schuchert in The Evolution of the Earth and Its In- 
habitants: Edited by B. S. Lull, New Haven, 1918, but with revisions by 
Professor Schuchert. 


Moreover, they could live in most latitudes, for the in 
direct evidences of life in the Archeozoic and Protero 
zoic rocks are widely distributed. Thus it appears tha 
at an almost incredibly early period, perhaps many hun 
dred million years ago, the earth's climate diflFered onl| 
a little from that of the present. 

The extreme limits of temperature beyond which t 
climate of geological times cannot have departed can 
approximately determined. Today the warmest parts 
the ocean have an average temperature of about 30**G 
on the surface. Only a few forms of life live where thi 
average temperature is much higher than this. In desert 
to be sure, some highly organized plants and animals ca 
for a short time endure a temperature as high as 75 
(167°F.). In certain hot springs, some of the lowest un 
cellular plant forms exist in water which is only a litt 
below the boiling point. More complex forms, howeve 
such as sponges, worms, and all the higher plants an 
animals, seem to be unable to live either in water or a 
where the temperature averages above 45°C. (113**P 
for any great length of time and it is doubtful wheth 
they can thrive permanently even at that temperatur 
The obvious unity of life for hundreds of millions 
years and its presence at all times in middle latitudes at 
far as we can tell seem to indicate that since the bo- 
ginning of marine life the temperature of the ocean 
cannot have averaged much above 50° C. even in the 
warmest portions. This is putting the limit too high 
rather than too low, but even so the warmest parts o 
the earth can scarcely have averaged much more thai 
20° warmer than at present. 

Turning to the other extreme, we may inquire hoM 
much colder than now the earth 's surface may have beei 
since life first appeared. Proterozoic fossils have been 


found in places where the present average temperature 
approaches 0**C. If those places should be colder than 
now by 30° C, or more, the drop in temperature at the 
equator would almost certainly be still greater, and the 
seas everywhere would be permanently frozen. Thus 
life would be impossible. Since the contrasts between 
summer and winter, and between the poles and the 
equator seem generally to have been less in the past than 
at present, the range through which the mean tempera- 
ture of the earth as a whole could vary without utterly 
destroying life was apparently less than would now be 
the case. 

These considerations make it fairly certain that for at 
least several hundred million years the average tempera- 
ture of the earth's surface has never varied more than 
perhaps 30** C. above or below the present level. Even this 
range of 60°C. (108°F.) may be double or triple the range 
that has actually occurred. That the temperature has not 
passed beyond certain narrow limits, whatever their 
exact degree, is clear from the fact that if it had done so, 
all the higher forms of life would have been destroyed. 
Certain of the lowest unicellular forms might indeed have 
persisted, for when dormant they can stand great ex- 
tremes of dry heat and of cold for a long time. Even 
so, evolution would have had to begin almost anew. The 
supposition that such a thing has happened is untenable, 
for there is no hint of any complete break in the record 
of life during geological times, — ^no sudden disappear- 
ance of the higher organisms followed by a long period 
with no signs of life other than indirect evidence such as 
occurs in the Archeozoic. 

A change of 60** C. or even of 20** in the average tem- 
perature of the earth's surface may seem large when 
viewed from the limited standpoint of terrestrial ex- 


perience. Viewed, however, from the standpoint of 
cosmic evolution, or even of the solar system, it seems 
a mere trifle. Consider the possibilities. The tempera- 
ture of empty space is the absolute zero, or — 273 °C. 
To this temperature all matter must fall, provided it 
exists long enough and is not appreciably heated by colli- 
sions or by radiation. At the other extreme lies the 
temperature of the stars. As stars go, our sun is only 
moderately hot, but the temperature of its surface is 
calculated to be nearly 7000** C, while thousands of miles 
in the interior it may rise to 20,000'' or lOOjOOO"* or some 
other equally unknowable and incomprehensible figure. 
Between the limits of the absolute zero on the one hand, 
and the interior of a sun or star on the other, there is 
almost every conceivable possibility of temperature. 
Today the earth *s surface averages not far from 14** C, 
or 287** above the absolute zero. Toward the interior, 
the temperature in mines and deep wells rises about l^'C. 
for every 100 meters. At this rate it would be over 500° C. 
at a depth of ten miles, and over 5000° at 100 miles. 

Let us confine ourselves to surface temperatures, 
which are all that concern us in discussing climate. It 
has been calculated by Poynting" that if a small sphere 
absorbed and re-radiated all the heat that fell upon it, 
its temperature at the distance of Mercury from the sun 
would average about 210 **C.; at the distance of Venus, 
85^ ; the earth 27° ; Mars —30° ; Neptune —219°. A planet 
much nearer the sun than is Mercury might be heated to 
a temperature of a thousand, or even several thousand, 
degrees, while one beyond Neptune would remain almost 
at absolute zero. It is well within the range of possibility 
that the temperature of a planet's surface should be 

» J. H. Poynting: Kadiation in the Solar System; Phil. Trans. A, 1903, 
202, p. 525. 


anywhere from near — 273''C. up to perhaps 5000°C. or 
more, although the probability of low temperature is 
much greater than of high. Thus throughout the whole 
vast range of possibilities extending to perhaps 10,000**, 
the earth claims only 60® at most, or less than 1 per cent. 
This may be remarkable, but what is far more remark- 
able is that the earth's range of 60° includes what seem 
to be the two most critical of all possible temperatures, 
namely, the freezing point of water, 0**C., and the tem- 
perature where water can dissolve an amount of carbon 
dioxide equal to its own volume. The most remarkable 
fact of all is that the earth has preserved its temperature 
within these narrow limits for a hundred million years, 
or perchance a thousand million. 

To appreciate the extraordinary significance of this 
last fact, it is necessary to realize how extremely critical 
are the temperatures from about 0** to 40° C, and how 
difficult it is to find any good reason for a relatively 
uniform temperature through hundreds of millions of 
years. Since the dawn of geological time the earth's 
temperature has apparently always included the range 
from about the freezing point of water up to about the 
point where protoplasm begins to disintegrate. Hender- 
son, in The Fitness of the Environment, rightly says that 
water is *'the most familiar and the most important of 
all things." In many respects water and carbon dioxide 
form the most unique pair of substances in the whole 
realm of chemistry. Water has a greater tendency than 
any other known substance to remain within certain 
narrowly defined limits of temperature. Not only does it 
have a high specific heat, so that much heat is needed to 
raise its temperature, but on freezing it gives up more 
heat than any substance except ammonia, while none of 
the couMnon liquids approach it in the amount of addi- 


tional heat required for conversion into vapor after the 
temperature of vaporization has been reached. Again, 
water substance, as the physicists call all forms of H2O, 
is unique in that it not only contracts on melting, but 
continues to contract until a temperature several degrees 
above its melting point is reached. That fact has a vast 
importance in helping to keep the earth's surface at a 
uniform temperature. If water were like most liquids, 
the bottoms of all the oceans and even the entire body of 
water in most cases would be permanently frozen. 

Again, as a solvent there is literally nothing to com- 
pare with water. As Henderson* puts it: '* Nearly the 
whole science of chemistry has been built up around 
water and aqueous solution. ' ' One of the most significant 
evidences of this is the variety of elements whose pres- 
ence can be detected in sea water. According to Hender 
son they include hydrogen, oxygen, nitrogen, carbon, 
chlorine, sodimn, magnesium, sulphur, phosphorus, whicl 
are easily detected; and also arsenic, csBsium, gold 
lithium, rubidium, barium, lead, boron, fluorine, iron. 
iodine, bromine, potassium, cobalt, copper, manganese 
nickel, silver, silicon, zinc, aluminium, calcium, an^ 
strontium. Yet in spite of its marvelous power of solu 
tion, water is chemically rather inert and relatively 
stable. It dissolves all these elements and thousands 
their compounds, but still remains water and can easi 
be separated and purified. Another unique property 0: 
water is its power of ionizing dissolved substances, 
property which makes it possible to produce electri 
currents in batteries. This leads to an almost infini 
array of electro-chemical reactions which play an almos 
dominant role in the processes of life. Finally, nc 
common liquid except mercury equals water in its powei 

• Lw J. Henderson: The Fitness of the Environment^ 1913. ' 


of capillarity. This fact is of enormous moment in 
biology, most obviously in respect to the soil. 

Although carbon dioxide is far less familiar than 
water, it is almost as important. ^ ^ These two simple sub- 
stances, '* says Henderson, **are the common source of 
every one of the complicated substances which are pro- 
duced by living beings, and they are the common end 
products of the wearing away of all the constituents of 
protoplasm, and of the destruction of those materials 
which yield energy to the body. ' * One of the remarkable 
physical properties of carbon dioxide is its degree of 
solubility in water. This quality varies enormously in 
different substances. For example, at ordinary pressures 
and temperatures, water can absorb only about 5 per 
cent of its own volume of oxygen, while it can take up 
about 1300 times its own volume of ammonia. Now for 
carbon dioxide, unlike most gases, the volume that can 
be absorbed by water is nearly the same as the volume 
of the water. The volumes vary, however, according to 
temperature, being absolutely the same at a temperature 
of about 15°C. or 59^F., which is close to the ideal tem- 
perature for man's physical health and practically the 
same as the mean temperature of the earth's surface 
when all seasons are averaged together. ^^ Hence, when 
water is in contact with air, and equilibrium has been 
established, the amount of free carbonic acid in a given 
volume of water is ahnost exactly equal to the amount 
in the adjacent air. Unlike oxygen, hydrogen, and nitro- 
gen, carbonic acid enters water freely ; unlike sulphurous 
oxide and ammonia, it escapes freely from water. Thus 
the waters can never wash carbonic acid completely out 
of the air, nor can the air keep it from the waters. It is 
the one substance which thus, in considerable quantities 
relative to its total amount, everywhere accompanies 


water. In earth, air, fire, and water alike these two sub- 
stances are always associated. 

** Accordingly, if water be the first primary con- 
stituent of the environment, carbonic acid is inevitably 
the second, — ^because of its solubility possessing an 
equal mobility with water, because of the reservoir of the 
atmosphere never to be depleted by chemical action in 
the oceans, lakes, and streams. In truth, so close is the 
association between these two substances that it is 
scarcely correct logically to separate them at all; to- 
gether they make up the real environment and they never 
part company. ' " 

The complementary qualities of carbon dioxide and 
water are of supreme importance because these two are 
the only known substances which are able to form a vast 
series of complex compounds with highly varying chemi- 
cal formulae. No other known compounds can give oflf 
or take on atoms without being resolved back into their 
elements. No others can thus change their form freely 
without losing their identity. This power of change with- 
out destruction is the fundamental chemical character- 
istic of life, for life demands complexity, change, and 

In order that water and carbon dioxide may combine 
to form the compounds on which life is based, the water 
must be in the liquid form, it must be able to dissolve 
carbon dioxide freely, and the temperature must not be 
high enough to break up the highly complex and delicate 
compounds as soon as they are formed. In other words, 
the temperature must be above freezing, while it must 
not rise higher than some rather indefinite point between 
50° C. and the boiling point, where all water finally turns 
into vapor. In the whole range of temperature, so far as 

7 Henderson : loc, cit,, p. 138. 


we know, there is no other interval where any such com- 
plex reactions take place. The temperature of the earth 
for hundreds of millions of years has remained firmly 
fixed within these limits. 

The astonishing quality of the earth *s uniformity of 
temperature becomes still more apparent when we con- 
sider the origin of the sun's heat. What that origin is 
still remains a question of dispute. The old ideas of a 
burning sun, or of one that is simply losing an original 
supply of heat derived from some accident, such as colli- 
sion with another body, were long ago abandoned. The 
impact of a constant supply of meteors affords an ahnost 
equally unsatisfactory explanation. Moulton' states that 
if the sun were struck by enough meteorites to keep up 
its heat, the earth would almost certainly be struck by 
enough so that it would receive about half of 1 per cent 
as much heat from them as from the sun. This is millions 
of times more heat than is now received from meteors. 
If the sun owes its heat to the impact of larger bodies at 
longer intervals, the geological record should show a 
series of interruptions far more drastic than is actually 
the case. 

It has also been supposed that the sun owes its heat 
to contraction. If a gaseous body contracts it becomes 
warmer. Finally, however, it must become so dense that 
its rate of contraction diminishes and the process ceases. 
Under the sun's present condition of size and density a 
radial contraction of 120 feet per year would be enough 
to supply all the energy now radiated by that body. This 
seems like a hopeful source of energy, but Kelvin cal- 
culated that twenty million years ago it was ineffective 
and ten million years hence it will be equally so. More- 
over, if this is the source of heat, the amount of radia- 

8 F. B. Monlton : Introduction to Astronomj^ 1916. 


tion from the sun would have to vary enormously. 
Twenty million years ago the sun would have extended 
nearly to the earth *s orbit and would have been so tenu- 
ous that it would have emitted no more heat than some 
of the nebulae in space. Some millions of years later^ 
when the sun's radius was twice as great as at present, 
that body would have emitted only one-fourth as much 
heat as now, which would mean that on the earth's sur- 
face the theoretical temperature would have been 200** 
below the present level. This is utterly out of accord with 
the uniformity of climate shown by the geological record. 
In the future, if the sun 's contraction is the only source 
of heat, the sun can supply the present amount for only 
ten million years, which would mean a change utterly 
unlike anything of which the geological record holds 
even the faintest hint.' 

Altogether the problem of how the sun can have re- 
mained so uniform and how the earth's atmosphere and 
other conditions can also have remained so uniform 
throughout hundreds of millions of years is one of the 
most puzzling in the whole realm of nature. If appeal is 
taken to radioactivity and the breaking up of uranium 
into radium and helium, conditions can be postulated 
which will give the required amount of energy. Such is 
also the case if it be supposed that there is some unknown 
process which may induce an atomic change like radio- 
activity in bodies which are now supposed to be stable 
elements. In either case, however, there is as yet no 
satisfactory explanation of the uniformity of the earth's 
climate. A hundred million or a thousand million years 
ago the temperature of the earth's surface was very 
much the same as now. The earth had then presumably 
ceased to emit any great amount of heat, if we may judge 

• Moulton: loc. cit. 



from the fact that its surface was cool enough so that 
^eat ice sheets could accumulate on low lands within 40"^ 
of the equator. The atmosphere was apparently almost 
like that of today, and was almost certainly not different 
enough to make up for any great divergence of the sun 
from its present condition. We cannot escape the stu- 
pendous fact that in those remote times the sun must 
have been essentially the same as now, or else that some 
utterly imknown factor is at work. 


THE variability of the earth's climate is almost as 
extraordinary as its uniformity. This variabilit 
is made up partly of a long, slow tendency in on 
direction and partly of innumerable cycles of every con| 
ceivable duration from days, or even hours, up to million 
of years. Perhaps the easiest way to grasp the full co 
plexity of the matter is to put the chief types of climati 
sequence in the form of a table. 


1. Cosmic uniformity. 7. Bruckner periods. 

2. Secular progression. 8. Sunspot cycles. 

3. Geologic oscillations. 9. Seasonal alternations. 

4. Glacial fluctuations. 10. Pleionian migrations. 
6. Orbital precessions. 11. Cyclonic vacillations. 
6. Historical pulsations. 12. Daily vibrations. 

In assigning names to the various types an attempj 
has been made to indicate something of the nature of thi 
sequence so far as duration, periodicity, and general 
tendencies are concerned. Not even the rich English 
language of the twentieth century, however, fumisheg 
words with enough shades of meaning to express all tha 


is desired. Moreover, except in degree, there is no sharp 
distinction between some of the related types, such as 
glacial fluctuations and historic pulsations. Yet, taken as 
a whole, the table brings out the great contrast between 
two absolutely diverse extremes. At the one end lies well- 
nigh eternal uniformity, or an extremely slow progress in 
one direction throughout countless ages; at the other, 
rapid and regular vibrations from day to day, or else 
irregular and seemingly unsystematic vacillations due to 
cyclonic storms, both of which types are repeated mil- 
lions of times during even a single glacial fluctuation. 

The meaning of cosmic uniformity has been explained 
in the preceding chapter. Its relation to the other types 
of climatic sequences seems to be that it sets sharply 
defined limits beyond which no changes of any kind have 
ever gone since life, as we know it, first began. Secular 
progression, on the other hand, means that in spite of all 
manner of variations, now this way and then the other, 
the normal climate of the earth, if there is such a thing, 
has on the whole probably changed a little, perhaps be- 
coming more complex. After each period of continental 
uplift and glaciation — for such are preeminently the 
times of complexity— it is doubtful whether the earth has 
ever returned to quite its former degree of monotony. 
Today the earth has swung away from the great diversity 
of the glacial period. Yet we still have contrasts of what 
seem to us great magnitude. In low depressions, such as . 
Turfan in the central deserts of Eurasia, the thermom- 
eter sometimes ranges from 0**F. in the morning to 60** 
in the shade at noon. On a cloudy day in the Amazon 
forest close to the seashore, on the contrary, the tempera- 
ture for months may rise to 85** by day and sink no lower 
than 75** at night. 

The reasons for the secular progression of the earth *s 


climate appear to be intimately connected with those 
which have caused the next, and, in many respects, more 
important type of climatic sequence, which consists of 
geological oscillations. Both the progression and the 
oscillations seem to depend largely on three purely ter- 
restrial factors: first, the condition of the earth's in- 
terior, including both internal heat and contraction; 
second, the salinity and movement of the ocean; and 
third, the composition and amount of the atmosphere^ 
To begin with the earth's interior — ^its loss of heat ap- 
pears to be an almost negligible factor in explaining 
either secular progression or geologic oscillation. Accord- 
ing to both the nebular and the planetesimal hypotheses, 
the earth's crust appears to be colder now than it was 
hundreds or thousands of millions of years ago. Th« 
emission of internal heat, however, had probably ceased 
to be of much climatic significance near the beginning or 
the geological record, for in southern Canada glaciatioi 
occurred very early in the Proterozoic era. On the other 
hand, the contraction of the earth has produced remark- 
able eflfects throughout the whole of geological time. l! 
has lessened the earth's circumference by a thousand 
miles or more, as appears from the way in which th» 
rocks have been folded and thrust bodily over ovk 
another. According to the laws of dynamics this muak 
have increased the speed of the earth's rotation, thui 
shortening the day, and also having the more importani 
effect of increasing the bulge at the equator. On the othei 
hand, recent investigations indicate that tidal retardatioi 
has probably diminished the earth's rate of rotatioi 
more than seemed probable a few years ago, thus length- 
ening the day and diminishing the bulge at the equator 
Thus two opposing forces have been at work, one caus- 
ing acceleration and one retardation. Their combined 


jffect may have been a factor in causing secular progres- 
lion of climate. It almost certainly was of much im- 
)ortance in causing pronounced oscillations first one way 
ind then the other. This matter, together with most of 
hose touched in these first chapters, will be expanded in 
ater parts of the book. On the whole the tendency ap- 
pears to have been to create climatic diversity in place 
tf uniformity. 

The increasing salinity of the oceans may have been 
jQother factor in producing secular progression, al- 
hough of slight importance in respect to oscillations. 
Vhile the oceans were still growing in volume, it is gen- 
rally assumed that they must have been almost fresh 
or a vast period, although Chamberlin thinks that the 
hange in salinity has been much less than is usually 
apposed. So far as the early oceans were fresher than 
dose of today, their deep-sea circulation must have been 
»ss hampered than now by the heavy saline water which 
J produced by evaporation in warm regions. Although 
tiis saline water is warm, its weight causes it to descend, 
istead of moving poleward in a surface current; this 
escent slows up the rise of the cold water which has 
loved along in the depths of the ocean from high lati- 
ides, and thus checks the general oceanic circulation, 
f the ancient oceans were fresher and hence had a freer 
irculation than now, a more rapid interchange of polar 
od equatorial water presumably tended to equalize the 
[imate of all latitudes. 

Again, although the earth's atmosphere has probably 
[langed far less during geological times than was 
>rmerly supposed, its composition has doubtless varied, 
'he total volume of nitrogen has probably increased, for 
xat gas is so inert that when it once becomes a part of 
le air it is almost sure to stay there. On the other hand. 


the proportions of oxygen, carbon dioxide, and wfi 
vapor must have fluctuated. Oxygen is taken out c 
stantly by animals and by all the processes of i 
weathering, but on the other hand the supply is increa 
when plants break up new carbon dioxide derived fi 
volcanoes. As for the carbon dioxide, it appears pi 
able that in spite of the increased supply fumishec 
volcanoes the great amounts of carbon which have gr^ 
ally been locked up in coal and limestone have apj 
ciably depleted the atmosphere. Water vapor also I 
be less abundant now than in the past, for the presi 
of carbon dioxide raises the temperature a little 
thereby enables the air to hold more moisture. When 
area of the oceans has diminished, and this has recu 
very often, this likewise would tend to reduce the w 
vapor. Moreover, even a very slight diminution in 
amount of heat given off by the earth, or a decrea 
evaporation because of higher salinity in the oc 
would tend in the same direction. Now carbon dioxide 
water vapor both have a strong blanketing effect whe 
heat is prevented from leaving the earth. Therefore 
probable reduction in the carbon dioxide and w 
vapor of the earth's atmosphere has apparently te 
to reduce the climatic monotony and create diversit 
complexity. Hence, in spite of many reversals, the 
eral tendency of changes, not only in the earth 's intej 
and in the oceans, but also in the atmosphere, appean 
be a secular progression from a relatively monotoi 
climate in which the evolution of higher organic fc 
would scarcely be rapid to an extremely diverse 
complex climate highly favorable to progressive e\ 
tion. The importance of these purely terrestrial ager 
must not be lost sight of when we come to discuss o 
agencies outside the earth. 


In Table 2 the next type of climatic sequence is geo- 
^gie oscillation. This means slow swings that last 
lillions of years. At one extreme of such an oscillation 
le climate all over the world is relatively monotonous ; 
. returns, as it were, toward the primeval conditions at 
le beginning of the secular progression. At such times 
lagnoUas, sequoias, figs, tree ferns, and many other 
npes of s;btropical plants grew far north in plaL Uke 
reenland, as is well known from their fossil remains of 
dddle Cenozoic time, for example. At these same times, 
ad also at many others before such high types of plants 
ad evolved, reef-making corals throve in great abun- 
ance in seas which covered what is now Wisconsin, 
[ichigan, Ontario, and other equally cool regions. Today 
lese regions have an average temperature of only about 
0**F. in the warmest month, and average well below 
reezing in winter. No reef -making corals can now live 
^here the temperature averages below 68° F. The re- 
^mblance of the ancient corals to those of today makes 
; highly probable that they were equally sensitive to low 
jmperature. Thus, in the mild portions of a geologic 
Bcillation the climate seems to have been so equable and 
niform that many plants and animals could live 1500 
nd at other times even 4000 miles farther from the 
quator than now. 

At such times the lands in middle and high latitudes 
rere low and small, and the oceans extended widely over 
lie continental platforms. Thus unhampered ocean cur- 
ents had an opportunity to carry the heat of low lati- 
ades far toward the poles. Under such conditions, es- 
pecially if the conception of the great subequatorial 
ontinent of Gondwana land is correct, the trade winds 
nd the westerlies must have been stronger and steadier 
ban now. This would not only enable the westerlies. 


which are really southwesterlies, to carry more heat th< 
now to high latitudes, but would still further strength 
the ocean currents. At the same time, the air presuma 
contained an abundance of water vapor derived fr< 
the broad oceans, and an abundance of atmosph 
carbon dioxide inherited from a preceding time w 
volcanoes contributed much carbon dioxide to the 
These two constituents of the atmosphere may h 
exercised a pronounced blanketing effect whereby k 
heat of the earth with its long wave lengths was kepti 
although the energy of the sun with its shorter wn 
lengths was not markedly kept out. Thus everything rif 
have combined to produce mild conditions in high li 
tudes, and to diminish the contrast between equator d 
pole, and between summer and winter. 

Such conditions perhaps carry in themselves the SGBi 
of decay. At any rate while the lands lie quiet durinji 
period of mild climate great strains must accumulate! 
the crust because of the earth's contraction and tii 
retardation. At the same time the great abundance' 
plants upon the lowlying plains with their mild climai 
and the marine creatures upon the broad contineiji 
platforms, deplete the atmospheric carbon dioxide. Rs 
of this is locked up as coal and part as limestone derini 
from marine plants as well as animals. Then somethj{ 
happens so that the strains and stresses of the crust ^ 
released. The sea floors sink; the continents becol 
relatively high and large ; mountain ranges are tormi 
and the former plains and emergent portions of t 
continental platforms are eroded into hills and valle^ 
The large size of the continents tends to create deseH 
and other types of climatic diversity; the presence ^ 
mountain ranges checks the free flow of winds and 
creates diversity; the ocean currents are like 


checked^ altered, and diverted so that the flow of heat 
from low to high latitudes is diminished. At the same 
time evaporation from the ocean diminishes so that a 
decrease in water vapor combines with the previous de- 
pletion of carbon dioxide to reduce the blanketing effect 
of the atmosphere. Thus upon periods of mild monotony 
there supervene periods of complexity, diversity, and 
severity. Turn to Table 1 and see how a glacial climate 
again and again succeeds a time when relative mildness 
prevailed almost everywhere. Or examine Fig. 1 and 
notice how the lines representing temperatures go up and 
down. In the figure Schuchert makes it clear that when 
the lands have been large and mountain-making has been 
important, as shown by the high parts of the lower shaded 
area, the cUmate has been severe, as shown by the descent 
of the snow line, the upper shaded area. In the diagram 
the climatic oscillations appear short, but this is merely 
because they have been crowded together, especially in 
the left hand or early part. There an inch in length may 
represent a hundred million years. Even at the right- 
liand end an inch is equivalent to several million years. 

The severe part of a climatic oscillation, as well as the 
mild part, will be shown in later chapters to bear in itself 
certain probable seeds of decay. While the lands are 
being uplifted, volcanic activity is likely to be vigorous 
and to add carbon dioxide to the air. Later, as the moun- 
tains are worn down by the many agencies of water, 
wind, ice, and chemical decay, although much carbon 
'dioxide is locked up by the carbonation of the rocks, the 
carbon locked up in the coal is set free and increases the 
carbon dioxide of the air. At the same time the continents 
settle slowly downward, for the earth's crust though 
rigid as steel is nevertheless slightly viscous and will 
flow if subjected to sufficiently great and enduring pres- 


sure. The area from which evaporation can take place 
is thereby increased because of the spread of the oceans 
over the continents, and water vapor joins with the car- 
bon dioxide to blanket the earth and thus tends to keep it 
uniformly warm. Moreover, the diminution of the lands 
frees the ocean currents from restraint and permits them 
to flow more freely from low latitudes to high. Thus in 
the course of millions of years there is a return toward 
monotony. Ultimately, however, new stresses accumulate 
in the earth's crust, and the way is prepared for another 
great oscillation. Perhaps the setting free of the stresses 
takes place simply because the strain at last becomes 
irresistible. It is also possible, as we shall see, that an 
external agency sometimes adds to the strain and thereby 
determines the time at which a new oscillation shall 

In Table 2 the types of climatic sequences which fol- 
low ** geologic oscillations'' are *' glacial fluctuations," 
*' orbital precessions" and ** historical pulsations." 
Glacial fluctuations and historical pulsations appear to 
be of the same type, except as to severity and duration, 
and hence may be considered together. They will be 
treated briefly here because the theories as to their 
causes are outlined in the next two chapters. Oddly 
enough, although the historic pulsations lie much closer 
to us than do the glacial fluctuations, ihej were not 
discovered until two or three generations later, and are 
still much less known. The most important feature of 
both sequences is the swing from a glacial to an inter- 
glacial epoch or from the arsis or accentuated part of an 
historical pulsation to the thesis or unaccented part. In a 
glacial epoch or in the arsis of an historic pulsation, 
storms are usually abundant and severe, the mean tem- 
perature is lower than usual, snow accumulates in high 







•3 ° 
• I 

A ;!! 

^^ i 



t^ o 

?« > 
O O 

® g" 







latitudes or upon lofty mountains. For example, in the 
last such period during the fourteenth century, great 
floods and droughts occurred alternately around the 
North Sea; it was several times possible to cross th« 
Baltic Sea from Germany to Sweden on the ice, and th* 
ice of Greenland advanced so much that shore ice caused 
the Norsemen to change their sailing route between Ice- 
land and the Norse colonies in southern Greenland. At 
the same time in low latitudes and in parts of the con- 
tinental interior there is a tendency toward diminishd 
rainfall and even toward aridity and the formation d 
deserts. In Yucatan, for example, a diminution in tropi- 
cal rainfall in the fourteenth century seems to have give 
the Mayas a last opportunity for a revival of their decaj 
ing civilization. 

Among the climatic sequences, glacial fluctuations aie 
perhaps of the most vital import from the standpoint i 
organic evolution ; from the standpoint of human histoij 
the same is true of climatic pulsations. Glacial epock 
have repeatedly wiped out thousands upon thousands i 
species and played a part in the origin of entirely net 
types of plants and animals. This is best seen when tic 
life of the Pennsylvanian is contrasted with that of tk 
Permian. An historic pulsation may wipe out an entiit 
civilization and permit a new one to grow up with a radh 
cally different character. Hence it is not strange that tk 
causes of such climatic phenomena have been discussel 
with extraordinary vigor. In few realms of science h* 
there been a more imposing or more interesting array d 
theories. In this book we shall consider the more impor- 
tant of these theories. A new solar or cyclonic hypothesi 
and the hypothesis of changes in the form and altitude d 
the land will receive the most attention, but the othei 


chief hypotheses are outlined in the next chapter, and are 
frequently referred to throughout the volume. 

Between glacial fluctuations and historical pulsations 
in duration, but probably less severe than either, come 
orbital precessions. These stand in a group by them- 
selves and are more akin to seasonal alternations than 
to any other type of climatic sequence. They must have 
occurred with absolute regularity ever since the earth 
began to revolve around the sun in its present elliptical 
orbit. Since the orbit is elliptical and since the sun is in 
one of the two foci of the ellipse, the earth's distance 
from the sun varies. At present the earth is nearest the 
sun in the northern winter. Hence the rigor of winter in 
the northern hemisphere is mitigated, while that of the 
southern hemisphere is increased. In about ten thousand 
years this condition will be reversed, and in another ten 
thousand the present conditions will return once more. 
Such climatic precessions, as we may here call them, 
must have occurred unnumbered times in the past, but 
they do not appear to have been large enough to leave in 
the fossils of the rocks any traces that can be distin- 
guished from those of other climatic sequences. 

We come now to Bruckner periods and sunspot cycles. 
The Bruckner periods have a length of about thirty-three 
years. Their existence was suggested at least as long ago 
as the days of Sir Francis Bacon, whose statement about 
them is quoted on the flyleaf of this book. They have 
since been detected by a careful study of the records of 
the time of harvest, vintage, the opening of rivers to 
navigation, and the rise or fall of lakes like the Caspian 
Sea. In his book on Klimaschwankungen seit 1700, 
Briickner has collected an uncommonly interesting assort- 
ment of facts as to the climate of Europe for more than 
two centuries. More recently, by a study of the rate of 


growth of trees, Douglass, in his book on Climatic Cycles 
and Tree Growth, has carried the subject still further. 
In general the nature of the 33-year periods seems to be 
identical with that of the 11- or 12- year sunspot cycle, 
on the one hand, and of historic pulsations on the other. 
For a century observers have noted that the variations 
in the weather which everyone notices from year to year 
seem to have some relation to sunspots. For generations, 
however, the relationship was discussed without leading 
to any definite conclusion. The trouble was that the same 
change was supposed to take place in all parts of the 
world. Hence, when every sort of change was found 
somewhere at any given sunspot stage, it seemed as 
though there could not be a relationship. Of late years, 
however, the matter has become fairly clear. The chief 
conclusions are, first, that when sunspots are numerous 
the average temperature of the earth ^s surface is lower 
than normal. This does not mean that all parts are cooler, 
for while certain large areas grow cool, others of less 
extent become warm at times of many sunspots. Second, 
at times of many sunspots storms are more abundant 
than usual, but are also confined somewhat closely to 
certain limited tracks so that elsewhere a diminution of 
storminess may be noted. This whole question is dis- 
cussed so fully in Earth and Sun that it need not detain 
us further in this preliminary view of the whole problem 
of climate. Suffice it to say that a study of the sunspot 
cycle leads to the conclusion that it furnishes a clue to 
many of the unsolved problems of the climate of the 
past, as well as a key to prediction of the future. 

Passing by the seasonal alternations which are fully 
explained as the result of the revolution of the earth 
around the sun, we may merely point out that, like the 
daily vibrations which bring Table 2 to a close, they 


emphasize the outstanding fact that the main control of 
terrestrial climate is the amount of energy received from 
the sun. This same principle is illustrated by pleionian 
migrations. The term **pleion^' comes from a Greek word 
meaning **more.'' It was taken by Arctowski to desig- 
nate areas or periods where there is an excess of some 
climatic element, such as atmospheric pressure^ rainfall, 
or temperature. Even if the effect of the seasons is elimi- 
nated, it appears that the course of these various ele- 
ments does not run smoothly. As everyone knows, a period 
like the autumn of 1920 in the eastern United States may 
be unusually warm, while a succeeding period may be 
unseasonably cool. These departures from the normal 
show a certain rough periodicity. For example, there is 
evidence of a period of about twenty-seven days, corre- 
sponding to the sun's rotation and formerly supposed to 
be due to the moon's revolution which occupies almost 
the same length of time. Still other periods appear to 
have an average duration of about three months and of 
between two and three years. Two remarkable discoveries 
have recently been made in respect to such pleions. One 
is that a given type of change usually occurs simulta- 
neously in a number of well-defined but widely separated 
centers, while a change of an opposite character arises 
in another equally well-defined, but quite different, set 
of centers. In general, areas of high pressure have one 
type of change and areas of low pressure the other type. 
So systematic are these relationships and so completely 
do they harmonize in widely separated parts of the earth, 
that it seems certain that they must be due to some out- 
side cause, which in all probability can be only the sun. 
The second discovery is that pleions, when once formed, 
travel irregularly along the earth 's surface. Their paths 
have not yet been worked out in detail, but a general 


migration seems well established. Because of this, it is 
probable that if unusually warm weather prevails in one 
part of a continent at a given time, the " thermo-pleion, * ' 
or excess of heat, will not vanish but will gradually move 
away in some particular direction. If we knew the path 
that it would follow we might predict the general tem- 
perature along its course for some months in advance. 
The paths are often irregular, and the pleions frequently 
show a tendency to break up or suddenly revive. Prob- 
ably this tendency is due to variations in the sun. When 
the sun is highly variable, the pleions are numerous and 
strong, and extremes of weather are frequent. Taken as 
a whole the pleions offer one of the most interesting and 
hopeful fields not only for the student of the causes of 
climatic variations, but for the man who is interested in 
the practical question of long-range weather forecasts. 
Like many other climatic phenomena they seem to repre- 
sent the combined effect of conditions in the sun and 
upon the earth itself. 

The last of the climatic sequences which require ex- 
planation is the cyclonic vacillations. These are familiar 
to everyone, for they are the changes of weather which 
occur at intervals of a few days, or a week or two, at all 
seasons, in large parts of the United States, Europe, 
Japan, and some of the other progressive parts of the 
earth. They do not, however, occur with great frequency 
in equatorial regions, deserts, and many other regions. 
Up to the end of the last century, it was generally sup- 
posed that cyclonic storms were purely terrestrial in 
origin. Without any adequate investigation it was as- 
sumed that all irregularities in the planetary circulation 
of the winds arise from an irregular distribution of heat 
due to conditions within or upon the earth itself. These 
irregularities were supposed to produce cyclonic storms 


in certain limited belts, but not in most parts of the 
world. Today this view is being rapidly modified. Un- 
doubtedly, the irregularities due to purely terrestrial 
conditions are one of the chief contributory causes of 
storms, but it begins to appear that solar variations also 
play a pari It has been found, for example, that not 
only the mean temperature of the earth 's surface varies 
in harmony with the sunspot cycle, but that the frequency 
and severity of storms vary in the same way. Moreover, 
it has been demonstrated that the sun's radiation is not 
constant, but is subject to innumerable variations. This 
does not mean that the sun 's general temperature varies, 
but merely that at some times heated gases are ejected 
rapidly to high levels so that a sudden wave of energy 
strikes the earth. Thus, the present tendency is to believe 
that the cyclonic variations, the changes of weather 
which come and go in such a haphazard, irresponsible 
way, are partly due to causes pertaining to the earth 
itself and partly to the sun. 

From this rapid survey of the types of climatic se- 
qnences, it is evident that they may be divided into four 
^eat groups. First comes cosmic uniformity, one of the 
most marvelous and incomprehensible of all known facts. 
We simply have no explanation which is in any respect 
adequate. Next come secular progression and geologic 
oscillations, two types of change which seem to be due 
mainly to purely terrestrial causes, that is, to changes in 
the lands, the oceans, and the air. The general tendency 
of these changes is toward complexity and diversity, thus 
producing progression, but they are subject to frequent 
reversals which give rise to oscillations lasting millions 
of years. The processes by which the oscillations take 
place are fully discussed in this book. Nevertheless, be- 
cause they are fairly well understood, they are deferred 


until after the third group of sequences has been dis- 
cussed. This group includes glacial fluctuations, historic 
pulsations, Briickner periods, sunspot cycles, pleionian 
migrations, and cyclonic vacillations. The outstanding 
fact in regard to all of these is that while they are greaily 
modified by purely terrestrial conditions, they seem to 
owe their origin to variations in the sun. They form the 
chief subject of Earth and Sun and in their larger phases 
are the most important topic of this book also. The last 
group of sequences includes orbital precessions, seasoiial 
alternations, and daily variations. These may be re- 
garded as purely solar in origin. Yet their influence, like 
that of each of the other groups, is much modified by the 
earth *s own conditions. Our main problem is to separate 
and explain the two great elements in climatic changes, 
— the effects of the sun, on the one hand, and of the earth 
on the other. 


THE next step in onr study of climate is to review 
the main hypotheses as to the causes of glada- 
tion. These hypotheses apply also to other types 
of climatic changes. We shall concentrate on glacial 
periods, however, not only because they are the most 
dramatic and well-known types of change, but because 
they have been more discussed than any other and have 
also had great influence on evolution. Moreover, they 
stand near the middle of the types of climatic sequences, 
and an imderstanding of them does much to explain the 
others. In reviewing the various theories we shaU not 
attempt to cover all the ground, but shall merely state 
the main ideas of the few theories which have had an 
important influence upon scientific thought. 

The conditions which any satisfactory climatic hy- 
pothesis must satisfy are briefly as follows : 

(1) Due weight must be given to the fact that changes 
of climate are almost certainly due to the combined effect 
of a variety of causes, both terrestrial and solar or 

(2) Attention must also be paid to both sides in the 
long controversy as to whether glaciation is due pri- 
marily to a diminution in the earth 's supply of heat or to 
a redistribution of the heat through changes in atmos- 
pheric and oceanic circulation. At present the great 


majority of authorities are on the side of a diminution of 
heat, but the other view also deserves study. 

(3) A satisfactory hypothesis must explain the fiie- 
quent synchronism between two great types of phe- 
nomena; first, movements of the earth's crust whereby 
continents are uplifted and mountains upheaved; and, 
second, great changes of climate which are usually 
marked by relatively rapid oscillations from one extreme 
to another. 

(4) No hypothesis can find acceptance unless it satis- 
fies the somewhat exacting requirements of the geolo^cal 
record, with its frequent but irregular repetition of long, 
mild periods, relatively cool or intermediate periods like 
the present, and glacial periods of more or less severity 
and perhaps accompanying the more or less widespr4»d 
uplifting of continents. At least during the later glacial 
periods the hypothesis must explain numerous cUmatic 
epochs and stages superposed upon a single general 
period of continental upheaval. Moreover, although lis- 
torical geology demands cycles of varied duration and 
magnitude, it does not furnish evidence of any rij^d 
periodicity causing the cycles to be uniform in length or 

(5) Most important of all, a satisfactory explanation 
of climatic changes and crustal deformation must take 
account of all the agencies which are now causing similar 
phenomena. Whether any other agencies should be con- 
sidered is open to question, although the relative im- 
portance of existing agencies may have varied. 

I. CrolVs Eccentricity Theory. One of the most in- 
genious and most carefully elaborated scientific hy- 
potheses is CroU's* precessional hypothesis as to ihe 
effect of the earth's own motions. So well was this worhed 

1 James Croll: Climate and Time, 1876. 


^ out that it was widely accepted for a time and still finds a 
place in popular but unscientific books, such as Wells' 
Outline of History, and even in scientific works like 
Wright's Quaternary Ice Age. The gist of the hypothe- 
sis has already been given in connection with the type of 
climatic sequence known as orbital precessions. The earth 
is 93 million miles away from the sun in January and 97 
million in July. The earth's axis **precesses," however, 
just as does that of a spi^ming top. Hence arises what is 
known as the precession of the equinoxes, that is, a 
steady change in the season at which the earth is in peri- 
helion, or nearest to the sun. In the course of 21,000 years 
the time of perihelion varies from early in January 
through the entire twelve months and back to January. 
Moreover, the earth's orbit is slightly more elliptical at 
certain periods than at others, for the planets sometimes 
become bunched so that they all pull the earth in one 
direction. Hence, once in about one hundred thousand 
years the effect of the elliptical shape of the earth 's orbit 
is at a maximum. 

GroU argued that these astronomical changes must 
alter the earth's climate, especially by their effect on 
winds and ocean currents. His elaborate argument con- 
tains a vast amount of valuable material. Later investi- 
gation, however, seems to have proven the inadequacy of 
his hypothesis. In the first place, the supposed cause does 
not seem nearly sufficient to produce the observed results. 
Second, CroU 's hypothesis demands that glaciation in the 
northern and southern hemisphere take place alternately. 
A constantly growing collection of facts, however, indi- 
cates that glaciation does not occur in the two hemi- 
spheres alternately, but at the same time. Third, the 
hypothesis calls for the constant and frequent repetition 
of glaciation at absolutely regular intervals. The geo- 


logical record shows no such regularity, for sometimeB 
several glacial epochs follow in relatively close succe^ 
sion at irregular intervals of perhaps fifty to two hun- 
dred thousand years, and thus form a glacial period ; and 
then for millions of years there are none. Fourth, the 
eccentricity hypothesis provides no adequate explanation 
for the glacial stages or subepochs, the historic pulsa- 
tions, and the other smaller climatic variations which are 
superposed upon glacial epochs and upon one another in 
bewildering confusion. In spite of these objections, tkere 
can be little question that the eccentricity of the earth's 
orbit and the precession of the equinoxes with the result- 
ing change in the season of perihelion must have some 
climatic effect. Hence CroU's theory deserves a perma- 
nent though minor place in any full discussion of the 
causes of climatic changes. 

II. The Carbon Dioxide Theory. At about the time 
that the eccentricity theory was being relegated to a 
minor niche, a new theory was being developed which 
soon exerted a profound influence upon geological 
thought. Chamberlin,^ adopting an idea suggested by 

ST. C. Ghamberlin: An attempt to frame a working hypothesis of the 
eause of glaeial periods on an atmospheric basis; Jour. Geol., VoL Til, 
1899, pp. 545-584, 667-686, 757-787. 

T. C. Ghamberlin and B. D. Salisbury: Geology, Vol. II, 1906, pp. 98- 
106, 655-677, and VoL III, pp. 432-446. 

S. Arrhenius (Kosmische Physik, Vol. II, 1903, p. 503) carried out Bome 
investigations on carbon dioxide which have had a pronounced effect on 
later conclusions. 

F. Freeh adopted Arrhenius' idea and developed it in a paper entitled 
Ueber die Klima-Aenderungen der Geologischen Vergangenheit. Compte 
Bendu, Tenth (Mexico) Ck>ngr. GeoL Intern., 1907 (=1908), pp. 299-325. 

The exact origin of the carbon dioxide theory has been stated so variously 
that it seems worth while to give the exact facts. Prompted by the tag- 
geetion of Tyndall that glaciation might be due to depletion of atmospheric 
carbon dioxide, Ghamberlin worked up the essentials of his early vien 
before he saw any publication from Arrhenius, to* whom the idea has ofUn 
been attributed. In 1895 or earlier Ghamberlin began to give the carta 
dioxide hypothesis to his students and to discuss it before local scientiie 



Tyndall, fired the imagination of geologists by his skill- 
ftd exposition of the part played by carbon dioxide in 
causing climatic changes. Today this theory is probably 
more widely accepted than any other. We have already 
seen that the amount of carbon dioxide gas in the at- 
mosphere has a decided climatic importance. Moreover, 
there can be little doubt that the amount of that gas in 
the atmosphere varies from age to age in response to the 
extent to which it is set free by volcanoes, consumed by 
plants, combined with rocks in the process of weathering, 
dissolved in the ocean or locked up in the form of coal 
and limestone. The main question is whether such varia- 
tions can produce changes so rapid as glacial epochs and 
historical pulsations. 

Abundant evidence seems to show that the degree to 
which the air can be warmed by carbon dioxide is sharply 
limited. Humphreys, in his excellent book on the Physics 
of the Air, calculates that a layer of carbon dioxide forty 
centimeters thick has practically as much blanketing 
effect as a layer indefinitely thicker. In other words, forty 
centimeters of carbon dioxide, while having no appreci- 

bodies. In 1897 he prepared a paper on ''A Group of Hypotheses Bearing 
on Climatic Changes," Jour. Geol., Vol. V (1897), to be read at the meeting 
of the British Association at Toronto, basing his conclusions on Tyndall's 
determination of the eompetencj of carbon dioxide as an absorber of heat 
radiated from the earth. He had essentially completed this when a paper by 
Arrhenius "On the influence of carbonic acid in the air upon the tem- 
perature of the ground," PhiL Mag., 1896, pp. 237-276, first came to his 
attention. Chamberlin then changed his conservative, tentative statement of 
the functions of carbon dioxide to a more sweeping one based on Arrhenius ' 
very definite quantitative deductions from Langley's experiments. Both 
Langley and Arrhenius were then in the ascendancy of their reputations 
and seemingly higher authorities could scarcely have been chosen, nor a 
finer combination than experiment and physico-mathematical development. 
Arrhenius' deductions were later proved to have been overstrained, while 
Langley 's interpretation and even his observations were challenged. Cham- 
berlin 's latest views are more like his earlier and more conservative state- 


able effect on sunlight coming toward the earth, would 
filter out and thus retain in the atmosphere all the oat- 
going terrestrial heat that carbon dioxide is capable of 
absorbing. Adding more would be like adding another 
filter when the one in* operation has already done all that 
that particular kind of filter is capable of doing. Accord- 
ing to Humphreys ' calculations, a doubling of the carbon 
dioxide in the air would in itself raise the average tem- 
perature about 1.3°C. and further carbon dioxide would 
have practically no effect. Reducing the present supply 
by half would reduce the temperature by essentially the 
same amount. 

The effect must be greater, however, than would ap- 
pear from the figures given above, for any change in 
temperature has an effect on the amount of water vapor, 
which in turn causes further changes of temperature. 
Moreover, as Chamberlin points out, it is not clear 
whether Humphreys allows for the fact that when the 
40 centimeters of CO2 nearest the earth has been heated 
by terrestrial radiation, it in turn radiates half its heat 
outward and half inward. The outward half is all ab- 
sorbed in the next layer of carbon dioxide, and so on. 
The process is much more complex than this, but the end 
result is that even the last increment of CO2, that is, the 
outermost portions in the upper atmosphere, must ap- 
parently absorb an infinitesimally small amount of heat. 
This fact, plus the effect of water vapor, would seem to 
indicate that a doubling or halving of the amount of COs 
would have an effect of more than 1.3 °C. A change of 
even 2**C. above or below the present level of the earth's 
mean temperature would be of very appreciable climatic 
significance, for it is commonly believed that during the 
height of the glacial period the mean temperature was 
only 5° to 8°C. lower than now. 


Nevertheless, variations in atmospheric carbon dioxide 
do not necessarily seem competent to produce the rela- 
tively rapid climatic fluctuations of glacial epochs and 
historic pulsations as distinguished from the longer 
swings of glacial periods and geological eras. In Cham- 
berlin's view, as in ours, the elevation of the land, the 
modification of the currents of the air and of the ocean, 
and all that goes with elevation as a topographic agency 
constitute a primary cause of climatic changes. A special 
effect of this is the removal of carbon dioxide from the 
air by the enhanced processes of weathering. This, as he 
carefully states, is a very slow process, and cannot of 
itself lead to anything so sudden as the oncoming of 
glaciation. But here comes Chamberlin 's most distinctive 
contribution to the subject, namely, the hypothesis that 
changes in atmospheric temperature arising from varia- 
tions in atmospheric carbon dioxide are able to cause a 
reversal of the deep-sea oceanic circulation. 

According to Chamberlin 's view, the ordinary oceanic 
circulation of the greater part of geological time was 
the reverse of the present circulation. Warm water de- 
scended to the ocean depths in low latitudes, kept its heat 
while creeping slowly poleward, and rose in high lati- 
tudes producing the warm climate which enabled corals, 
for example, to grow in high latitudes. Chamberlin holds 
this opinion largely because there seems to him to be no 
other reasonable way to accoxmt for the enormously long 
warm periods when heat-loving forms of life lived in 
what are now polar regions of ice and snow. He explains 
this reversed circulation by supposing that an abundance 
of atmospheric carbon dioxide, together with a broad 
distribution of the oceans, made the atmosphere so warm 
that the evaporation in low latitudes was far more rapid 
than now. Hence the surface water of the ocean became 


a relatively concentrated brine. Such a brine is heavy 
and tends to sink, thereby setting up an oceanic circula- 
tion the reverse of that which now prevails. At present 
the polar waters sink because they are cold and henee 
contract. Moreover, when they freeze a certain amount 
of salt leaves the ice and thereby increases the salinity 
of the surrounding water. Thus the polar water sinks 
to the depths of the ocean, its place is taken by wanner 
and lighter water from low latitudes which moves pole- 
ward along the surface, and at the same time the cold 
water of the ocean depths is forced equatorward below 
the surface. But if the equatorial waters were so concen- 
trated that a steady supply of highly saline water kept 
descending to low levels, the direction of the circulation 
would have to be reversed. The time when this would 
occur would depend upon the delicate balance between 
the downward tendencies of the cold polar water and of 
the warm saline equatorial water. 

Suppose that while such a reversed circulation pre- 
vailed, the atmospheric CO2 should be depleted, and the 
air cooled so much that the concentration of the equa- 
torial waters by evaporation was no longer sufficient to 
cause them to sink. A reversal would take place, the 
present type of circulation would be inaugurated, and 
the whole earth would suffer a chill because the sur- 
face of the ocean would become cool. The cool surface- 
water would absorb carbon dioxide faster than the pre- 
vious warm water had done, for heat drives off gases 
from water. This would hasten the cooling of the at- 
mosphere still more, not only directly but by diminishing 
the supply of atmospheric moisture. The result would be 
glaciation. But ultimately the cold waters of the higher 
latitudes would absorb all the carbon dioxide they could 
hold, the slow equatorward creep would at length permit 


the cold water to rise to the surface in low latitudes. 
There the warmth of the equatorial sun and the depleted 
supply of carbon dioxide in the air would combine to 
cause the water to give up its carbon dioxide once more. 
If the atmosphere had been sufficiently depleted by that 
time, the rising waters in low latitudes might give up 
more carbon dioxide than the cold polar waters absorbed. 
Thus the atmospheric supply would increase, the air 
would again grow warm, and a tendency toward de- 
gladation, or toward an inter-glacial condition would 
arise. At such times the oceanic circulation is not sup- 
posed to have been reversed, but merely to have been 
checked and made slower by the increasing warmth. 
Thus inter-glacial conditions like those of today, or even 
considerably warmer, are supposed to have been pro- 
duced with the present type of circulation. 

The emission of carbon dioxide in low latitudes could 
not permanently exceed the absorption in high latitudes. 
After the present type of circulation was finally estab- 
lished, which might take tens of thousands of years, the 
two would gradually become equal. Then the conditions 
which originally caused the oceanic circulation to be 
reversed would again destroy the balance; the atmos- 
pheric carbon dioxide would be depleted ; the air would 
grow cooler; and the cycle of glaciation would be re- 
peated. Each cycle would be shorter than the last, for not 
only would the swings diminish Uke those of a pendulum, 
but the agencies that were causing the main depletion of 
the atmospheric carbon dioxide would diminish in inten- 
sity. Finally as the lands became lower through erosion 
and submergence, and as the processes of weathering 
became correspondingly slow, the air would gradually be 
able to accumulate carbon dioxide ; the temperature would 
increase ; and at length the oceanic circulation would be 


reversed again. When the warm saline waters of low lati- 
tudes finally began to sink and to set up a flow of warm 
water poleward in the depths of the ocean, a glacial 
period would definitely come to an end. 

This hypothesis has been so skillfully elaborated, and 
contains so many important elements that one can 
scarcely study it without profound admiration. We be- 
lieve that it is of the utmost value as a step toward tiie 
truth, and especially because it emphasizes the great 
function of oceanic circulation. Nevertheless, we are 
unable to accept it in full for several reasons, which 
may here be stated very briefly. Most of them will be dis- 
cussed fully in later pages. 

(1) While a reversal of the deep-sea circulation would 
undoubtedly be of great climatic importance and would 
produce a warm climate in high latitudes, we see no 
direct evidence of such a reversal. It is equally true that 
there is no conclusive evidence against it, and the possi- 
bility of a reversal must not be overlooked. There seem, 
however, to be other modifications of atmospheric and 
oceanic circulation which are able to produce the ob- 
served results. 

(2) There is much, and we believe conclusive, evidence 
that a mere lowering of temperature would not produce 
glaciation. What seems to be needed is changes in atmos- 
pheric circulation and in precipitation. The carbon 
dioxide hypothesis has not been nearly so fully developed 
on the meteorological side as in other respects. 

(3) The carbon dioxide hypothesis seems to demand 
that the oceans should have been almost as saline as now 
in the Proterozoic era at the time of the first known 
glaciation. Ohamberlin holds that such was the case, but 
the constant supply of saline material brought to the 
ocean by rivers and the relatively small deposition of 


such material on the sea floor seem to indicate that the 
eariy oceans must have been much fresher than those of 

(4) The carbon dioxide hypothesis does not attempt 
to explain minor climatic fluctuations such as post-glacial 
stages and historic pulsations, but these appear to be of 
the same nature as glacial epochs, differing only in 

(5) Another reason for hesitation in accepting the 
carbon dioxide hypothesis as a full explanation of glacial 
fluctuations is the highly complex and non-observational 
character of the explanation of the alternation of glacial 
and inter-glacial epochs and of their constantly decreas- 
ing length. 

(6) Most important of all, a study of the variations of 
weather and of climate as they are disclosed by present 
records and by the historic past suggests that there are 
now in action certain other causes which are competent 
to explain glaciation without recourse to a process whose 
action is beyond the realm of observation. 

These considerations lead to the conclusion that the 
carbon dioxide hypothesis and the reversal of the oceanic 
circulation should be regarded as a tentative rather than 
a final explanation of glaciation. Nevertheless, the action 
of carbon dioxide seems to be an important factor in pro- 
ducing the longer oscillations of climate from one geo- 
logical era to another. It probably plays a considerable 
part in preparing the way for glacial periods and in 
making it possible for other factors to produce the more 
rapid changes which have so deeply influenced organic 

III. The Form of the Land. Another great cause of 
climatic change consists of a group of connected phe- 
nomena dependent upon movements of the earth 's crust. 


As to the climatic potency of changes in the lands there 
is practical agreement among students of climatology 
and glaciation. That the height and extent of the conti- 
nents, the location, size, and orientation of mountain 
ranges, and the opening and closing of oceanic gateways 
at places like Panama, and the consequent diversion of 
oceanic currents, exert a profound effect upon cUniate 
can scarcely be questioned. Such changes may be intro- 
duced rapidly, but their disappearance is usually slow 
compared with the rapid pulsations to which climate has 
been subject during historic times and during stages of 
glacial retreat and advance, or even in comparison with 
the epochs into which the Pleistocene^ Permian, and 
perhaps earlier glacial periods have been divided. Hence, 
while crustal movements appear to be more important 
than the eccentricity of the earth's orbit or the amount of 
carbon dioxide in the air, they do not satisfactorily ex- 
plain glacial fluctuations, historic pulsations, and espe- 
cially the present little cycles of climatic change. All 
these changes involve a relatively rapid swing from one 
extreme to another, while an upheaval of a continent, 
which is at best a slow geologic process, apparently 
cannot be undone for a long, long time. Hence such an 
upheaval, if acting alone, would lead to a relatively long- 
lived climate of a somewhat extreme type. It would help 
to explain the long swings, or geologic oscillations be- 
tween a mild and uniform climate at one extreme, and a 
complex and varied climate at the other, but it would not 
explain the rapid climatic pulsations which are closely 
associated with great movements of the earth's crust. It 
might prepare the way for them, but could not cause 
them. That this conclusion is true is borne out by the fact 
that vast mountain ranges, like those at the close of the 
Jurassic and Cretaceous, are upheaved without bringing 


on glacial climates. Moreover, the marked Permian ice 
age follows long after the birth of the Hercynian Moun- 
tians and before the rise of others of later Permian 

IV. The Volcanic Hypothesis. In the search for some 
cause of climatic change which is highly eflScient and yet 
able to vary rapidly and independently, Abbot, Fowle, 
Humphreys, and others,' have concluded that volcanic 
eruptions are the missing agency. In Physics of the Air, 
Humphreys gives a careful study of the effect of vol- 
canic dust upon terrestrial temperature. He begins with 
a mathematical investigation of the size of dust particles, 
and their quantity after certain eruptions. He demon- 
strates that the power of such particles to defliect light of 
short wave-lengths coming from the sun is perhaps thirty 
times more than their power to retain the heat radiated 
in long waves from the earth. Hence it is estimated that 
if a Krakatoa were to belch forth dust every year or 
two, the dust veil might cause a reduction of about 6°C. 
in the earth ^s surface temperature. As in every such com- 
plicated problem, some of the author's assumptions are 
open to question, but this touches their quantitative and 
not their qualitative value. It seems certain that if vol- 
canic explosions were frequent enough and violent 
enough, the temperature of the earth 's surface would be 
considerably lowered. 

Actual observation supports this theoretical conclu- 
sion. Humphreys gathers together and amplifies all that 
he and Abbot and Fowle have previously said as to obser- 
vations of the sun's thermal radiation by means of the 

• C. G. Abbot and P. E. Fowle: Voleanoes and Climate; Smiths. Mise. 
GoU., VoL 60, 1913, 24 pp. 

W. J. HmnphreyB: Voleanie dost and other factors in the production of 
climatic and their possible relation to ice ages; Bull. Mount Weather 
Obeervatory, Vol. 6, Part 1, 1913, 26 pp. Also, Physics of the Air, 1920. 


pyrheliometer. This summing np of the relations between 
the heat received from the sun, and the occurrence of 
explosive volcanic eruptions leaves little room for doubt 
that at frequent intervals during the last century and a 
half a slight lowering of terrestrial temperature has 
actually occurred after great eruptions. Nevertheless, it 
does not justify Humphreys' final conclusion that ** phe- 
nomena within the earth itself suffice to modify its own 
climate, . . . that these and these alone have actually 
caused great changes time and again in the geologic 
past/' Humphreys sees so clearly the importance of the 
purely terrestrial point of view that he unconsciously 
slights the cosmic standpoint and ignores the important 
solar facts which he himself adduces elsewhere at con- 
siderable length. 

In addition to this the degree to which the temperature 
of the earth as a whole is influenced by volcanic eruptions 
is by no means so clear as is the fact that there is some 
influence. Arctowski,* for example, has prepared numer- 
ous curves showing the march of temperature month 
after month for many years. During the period from 
1909 to 1913, which includes the great eruption of Katmai 
in Alaska, low temperature is found to have prevailed at 
the time of the eruption, but, as Arctowski puts it, on the 
basis of the curves for 150 stations in all parts of the 
world : ' * The supposition that these abnormally low tem- 
peratures were due to the veil of volcanic dust produced 
by the Katmai eruption of June 6, 1912, is completely out 
of the question. If that had been the case, temperature 
would have decreased from that date on, whereas it was 
decreasing for more than a year before that date. ' ' 

^H. Arctowski: The Pleionian Cycle of Climatic Fluctuations; Awi . 
Jour. Sci., Vol. 42, 1916, pp. 27-33. See also Annals of the New York 
Academy of Sciences, Vol. 24, 1914. 


Koppen,* in his comprehensive study of temperature 
for a hundred years, also presents a strong argument 
against the idea that volcanic eruptions have an im- 
portant place in determining the present temperature of 
the earth. A volcanic eruption is a sudden occurrence. 
Whatever effect is produced by dust thrown into the air 
must occur within a few months, or as soon as the dust 
has had an opportunity to be wafted to the region in 
question. When the dust arrives, there will be a rapid 
drop through the few degrees of temperature which the 
dust is supposed to be able to account for, and thereafter 
a slow rise of temperature. If volcanic eruptions actually 
caused a frequent lowering of terrestrial temperature in 
the hundred years studied by Koppen, there should be 
more cases where the annual temperature is decidedly 
below the normal than where it shows a large departure 
in the opposite direction. The contrary is actually the 

A still more important argument is the fact that the 
earth is now in an intermediate condition of climate. 
Throughout most of geologic time, as we shall see again 
and again, the climate of the earth has been milder than 
now. Regions like Greenland have not been the seat of 
glaciers, but have been the home of types of plants which 
now thrive in relatively low latitudes. In other words, the 
earth is today only part way from a glacial epoch to what 
may be called the normal, mild climate of the earth — a 
climate in which the contrast from zone to zone was much 
less than now, and the lower air averaged warmer. Hence 
it seems impossible to avoid the conclusion that the 
cause of glaciation is still operating with considerable 

5W. Koppen: t^ber mehrjahrige Perioden der Witterung ins besondere 
ozer die Il-jahrige Periode der Temperatur. Also, Lufttemperaturen 
Sonnenflecke und Vulcanausbruche; Meteorologische Zeitsehrift, Vol. 7, 
1914, pp. 305-328. 



although diminished efficiency. But volcanic dust is 
obviously not operating to any appreciable extent at 
present, for the upper air is almost free from dust a large 
part of the time. 

Again, as Chamberlin suggests, let it be supposed that 
a Exakatoan eruption every two years would produce a 
glacial period. Unless the most experienced field workers 
on the glacial formations are quite in error, the various 
glacial epochs of the Pleistocene glacial period had a 
joint duration of at least 150,000 years and perhaps twice 
as much. That would require 75,000 Exakatoan eruptions. 
But where are the pits and cones of such eruptions? 
There has not been time to erode them away since the 
Pleistocene glaciation. Their beds of volcanic ash would 
presumably be as voluminous as the glacial beds, but 
there do not seem to be accumulations df any such size. 
Even though the same volcano suffered repeated explo- 
sions, it seems impossible to find sufficient fresh volcanic 
debris. Moreover, the volcanic hypothesis has not yet 
offered any mechanism for systematic glacial variations. 
Hence, while the hypothesis is important, we must search 
further for the full explanation of glacial fluctuations, 
historic pulsations, and the earth's present quasi-gladal 

V. The Hypothesis of Polar Wandering. Another hy- 
pothesis, which has some adherents, especially among 
geologists, holds that the position of the earth 's axis has 
shifted repeatedly during geological times, thus causing 
glaciation in regions which are not now polar. Astrophys- 
icists, however, are quite sure that no agency could 
radically change the relation between the earth and its 
axis without likewise altering the orbits of the planets to 
a degree that would be easily recognized. Moreover, the 
distribution of the centers of glaciation both in the Per- 


mian and Pleistocene periods does not seem to conform 
to this hypothesis. 

VI. The Thermal Solar Hypothesis. The only other 
explanations of the climatic changes of glacial and his- 
toric times which now seem to have much standing are 
two distinct and almost antagonistic solar hypotheses. 
One is the idea that changes in the earth's climate are 
dne to variations in the heat emitted by the snn and 
hence in the temperature of the earth. The other is the 
entirely different idea that climatic changes arise from 
solar conditions which cause a redistribution of the 
earth* s atmospheric pressure and hence produce changes 
in winds, ocean currents, and especially storms. This 
second, or *' cyclonic,'' hypothesis is the subject of a book 
entitled Earth and Sun, which is to be published as a 
companion to the present volume. It will be outlined in 
the next chapter. The other, or thermal, hypothesis may 
be dismissed briefly. Unquestionably a permanent change 
in the amount of heat emitted by the sun would perma- 
nently alter the earth's climate. There is absolutely no 
evidence, however, of any such change during geologic 
time. The evidence as to the earth's cosmic uniformity 
and as to secular progression is all against it. Suppose 
that for thirty or forty thousand years the sun cooled off 
enough so that the earth was as cool as during a glacial 
epoch. As gladation is soon succeeded by a mild climate, 
some agency would then be needed to raise the sun's 
temperature. The impact of a shower of meteorites might 
accomplish this, but that would mean a very sudden heat- 
ing, such as there is no evidence of in geological history. 
In fact, there is far more evidence of sudden cooUng than 
of sudden heating. Moreover, it is far beyond the bounds 
of probability that such an impact should be repeated 
again and again with just such force as to bring the cli- 


mate back almost to where it started and yet to allow for 
the slight changes which cause secular progression. 
Another and equally cogent objection to the thennal form 
of solar hypothesis is stated by Humphreys as follows: 
**A change of the solar constant obviously alters all sur- 
face temperatures by a roughly constant percentage. 
Hence a decrease of the heat from the sun would in gen- 
eral cause a decrease of the interzonal temperature 
gradients ; and this in turn a less vigorous atmospheric 
circulation, and a less copious rain or snowfall — exactly 
the reverse of the condition, namely, abundant precipita- 
tion, most favorable to extensive glaciation. ' ' 

This brings us to the end of the main hypotheses as to 
climatic changes, aside from the solar cyclonic hypothesis 
which will be discussed in the next chapter. It appears 
that variations in the position of the earth at perihelion 
have a real though slight influence in causing cycles with 
a length of about 21,000 years. Changes in the carbon 
dioxide of the air probably have a more important but 
extremely slow influence upon geologic oscillations. 
Variations in the size, shape, and height of the continents 
are constantly causing all manner of climatic complica- 
tions, but do not cause rapid fluctuations and pulsations. 
The eruption of volcanic dust appears occasionally to 
lower the temperature, but its potency to explain the 
complex climatic changes recorded in the rocks has prob- 
ably been exaggerated. Finally, although minor changes 
in the amount of heat given out by the sun occur con- 
stantly and have been demonstrated to have a climatic 
effect, there is no evidence that such changes are the main 
cause of the climatic phenomena which we are trying to 
explain. Nevertheless, in connection with other solar 
changes they may be of high importance. 


THE progress of science is made up of a vast suc- 
cession of hypotheses. The majority die in early 
infancy. A few live and are for a time widely 
accepted. Then some new hypothesis either destroys them 
completely or shows that, while they contain elements of 
truth, they are not the whole truth. Li the previous chap- 
ter we have discussed a group of hypotheses of this kind, 
and have tried to point out fairly their degree of truth so 
far as it can yet be determined. Li this chapter we shall 
outline still another hypothesis, the relation of which to 
present climatic conditions has been fuUy developed in 
Earth and Sun; while its relation to the past will be ex- 
plained in the present volume. This hypothesis is not 
supposed to supersede the others, for so far as they are 
true they cannot be superseded. It merely seems to ex- 
plain some of the many conditions which the other 
hypotheses apparently fail to explain. To suppose that 
it will suffer a fate more glorious than its predecessors 
would be presumptuous. The best that can be hoped is 
that after it has been pruned, enriched, and modified, it 
may take its place among the steps which finally lead to 
the goal of truth. 

In this chapter the new hypothesis will be sketched in 
broad outline in order that in the rest of this book the 
reader may appreciate the bearing of all that is said. 
Details of proof and methods of work will be omitted. 


since they are given in Earth and Sun. For the sake of 
brevity and clearness the main conclusions will be stated 
without the qualifications and exceptions which are fully 
explained in that volume. Here it will be necessary to 
pass quickly over points which depart radically from ac- 
cepted ideas, and which therefore must arouse serious 
question in the minds of thoughtful readers. That, how- 
ever, is a necessary consequence of the attempt which 
this book makes to put the problem of climate in such 
form that the argument can be followed by thoughtful 
students in any branch of knowledge and not merely by 
specialists. Therefore, the specialist can merely be asked 
to withhold judgment until he has read all the evidence 
as given in Earth and Sun, and then to condemn only 
those parts that are wrong and not the whole argument 
Without further explanation let us turn to our main 
problem. In the realm of climatology the most important 
discovery of the last generation is that variations in the 
weather depend on variations in the activity of the sun's 
atmosphere. The work of the great astronomer. New- 
comb, and that of the great climatologist, Koppen, have 
shown beyond question that the temperature of the 
earth *s surface varies in harmony with variations in the 
number and area of sunspots.^ The work of Abbot has 
shown that the amount of heat radiated from the sun also 
varies, and that in general the variations correspond with 
those of the sunspots, although there are exceptions, 
especially when the spots are fewest. Here, however, 
there at once arises a puzzling paradox. The earth cer- 

1 The so-called sunspot numbers to which reference is made again and 
again in this book are based on a system devised by Wolf and revised bj 
A. Wolf er. The nmnber and size of the spots are both taken into account. 
The numbers from 1749 to 1900 may be found in the Monthly Weather 
Beyiew for April, 1902, and from 1901 to 1918 in the same journal for 


tainly owes its warmth to the sun. Yet when the sun emits 
the most energy, that is, when sunspots are most numer- 
ous, the earth's surface is coolest. Doubtless the earth 
receives more heat than usual at such times, and the 
upper air may be warmer than usual. Here we refer only 
to the air at the earth's surface. 

Another large group of investigators have shown thaij 
atmospheric pressure also varies in harmony with the 
number of sunspots. Some parts of the earth's surface 
have one kind of variation at times of many sunspots and 
other parts the reverse. These differences are systematic 
and depend largely on whether the region in question 
happens to have high atmospheric pressure or low. The 
net result is that when sunspots are numerous the 
earth's storminess increases, and the atmosphere is 
thrown into commotion. This interferes with the stable / 
planetary winds, such as the trades of low latitudes and/ 
the prevailing westerlies of higher latitudes. Instead of 
these regular winds and the fair weather which they 
biing, there is a tendency toward frequent tropical hurri- 
canes in the lower latitudes and toward more frequent 
and severe storms of the ordinary type in the latitudes 
where the world's most progressive nations now live. 
With the change in storminess there naturally goes a 
change in rainfall. Not all parts of the world, however, \ 
have increased storminess and more abundant rainfall \ 
when sunspots are numerous. Some parts change in the I 
opposite way. Thus when the sun's atmosphere is par- I 
ticularly disturbed, the contrasts between different parts / 
of the earth's surface are increased. For example, the / 
northern United States and southern Canada become 
more stormy and rainy, as appears in Fig. 2, and the 
same is true of the Southwest and along the south Atlan- 
tic coast. In a crescent-shaped central area, however. 


extending from Wyoming through Missouri to Nova 
Scotia, the namber of storms and the amotmt of rainfall 

The two controlling factors of any climate are the 
temperature and the atmospheric pressure, for they de- 
termine the winds, the storms, and thus the rainfall. A 
study of the temperature seems to show that the peculiar 
paradox of a hot sun and a cool earth is due largely to 
the increased storminess dnring times of many sunspots. 
The earth's surface is heated by the rays of the sun, but 

Fig. 2. Storminess at sunspot maodma vs. minima. 

(After Kitamer.-} 

Based on nine gears' Dearest sunapot minima and nine jears' nearest sun- 
spot maxima in tlie three annspot cycles from 1888 to 1918. Heavy shading 
indicates excess of stormineas when ennspots are Dumerous. FJgnree indieat* 
averase yearly number of atorms by which years of nuLXimiun aonspota 
exceed those of minimam sunspots. 


most of the rays do not in themselves heat the air as 
they pass through it. The air gets its heat largely from 
the heat absorbed by the water vapor which is intimately 
mingled with its lower portions, or from the long heat 
waves sent out by the earth after it has been warmed by 
the sun. The faster the air moves along the earth's sur- 
face the less it becomes heated, and the more heat it takes 
away. This sounds like a contradiction, but not to anyone 
who has tried to heat a stove in the open air. If the air 
is still, the stove rapidly becomes warm and so does the 
air around it. If the wind is blowing, the cool air delays 
the heating of the stove and prevents the surface from 
ever becoming as hot as it would otherwise. That seems 
to be what happens on a large scale when sunspots are 
numerous. The sun actually sends to the earth more 
energy than usual, but the air moves with such unusual 
rapidity that it actually cools the earth 's surface a trifle 
by carrying the extra heat to high levels where it is lost 
into space. 

There has been much discussion as to why storms are 
numerous when the sun's atmosphere is disturbed. Many 
investigators have supposed it was due entirely and 
directly to the heating of the earth's surface by the sun. 
This, however, needs modification for several reasons. 
In the first place, recent investigations show that in a 
great many cases changes in barometric pressure precede 
changes in temperature and apparently cause them by 
altering the winds and producing storms. This is the 
opposite of what would happen if the effect of solar heat 
upon the earth's surface were the only agency. In the 
second place, if storms were due exclusively to variations 
in the ordinary solar radiation which comes to the earth 
as light and is converted into heat, the solar effect ought 


to be most pronounced when the center of the sun's 
visible disk is most disturbed. As a matter of fact the 
storminess is notably greatest when the edges of the 
solar disk are most disturbed. These facts and others lead 
to the conclusion that some agency other than heat must 
also play some part in producing storminess. 

The search for this auxiliary agency raises many diffi- 
cult questions which cannot yet be answered. On the 
whole the weight of evidence suggests that electrical 
phenomena of some kind are involved, although varia- 
tions in the amount of ultra-violet light may also be 
important. Many investigators have shown that the sun 
emits electrons. Hale has proved that the sun, like the 
earth, is magnetized. Sunspots also have magnetic fields 
the strength of which is often fifty times as great as that 
of the sun as a whole. If electrons are sent to the earth, 
they must move in curved paths, for they are deflected 
by the sun's magnetic field and again by the earth's 
magnetic field. The solar deflection may cause their 
effects to be greatest when the spots are near the sun's 
margin; the terrestrial deflection may cause concentra- 
tion in bands roughly concentric with the magnetic poles 
of the earth. These conditions correspond with the known 

Farther than this we cannot yet go. The calculations of 
Humphreys seem to indicate that the direct electrical 
effect of the sun's electrons upon atmospheric pressure 
is too small to be of appreciable significance in intensify- 
ing storms. On the other hand the peculiar way in which 
activity upon the margins of the sun appears to be corre- 
lated not only with atmospheric! electricity, but with 
barometric pressure, seems to be equally strong evidence 
in the other direction. Possibly the sun's electrons and 
its electrical waves produce indirect effects by being 


converted into heat^ or by causing the formation of ozone 
and the condensation of water vapor in the upper air. 
Any one of these processes would raise the temperature 
of the upper air, for the ozone and the water vapor would 
be formed there and would tend to act as a blanket to 
hold in the earth's heat. But any such change in the tem- 
perature of the upper air would influence the lower air 
through changes in barometric pressure. These con- 
siderations are given here because the thoughtful reader 
is likely to inquire how solar activity can influence 
storminess. Moreover, at the end of this book we shall 
take up certain speculative questions in which an elec- 
trical hypothesis will be employed. For the main por- 
tions of this book it makes no difference how the sun's 
variations influence the earth's atmosphere. The only 
essential point is that when the solar atmosphere is active 
the storminess of the earth increases, and that is a matter 
of direct observation. 

Let us now inquire into the relation between the small 
cyclonic vacillations of the weather and the types of 
climatic changes known as historic pulsations and glacial 
fluctuations. One of the most interesting results of recent 
investigations is the evidence that sunspot cycles on a 
small scale present almost the same phenomena as do 
historic pulsations and glacial fluctuations. For instance, 
when sunspots are numerous, storminess increases 
markedly in a belt near the northern border of the area 
of greatest storminess, that is, in southern Canada and 
thence across the Atlantic to the North Sea and Scandi- 
navia. (See Figs. 2 and 3.) Corresponding with this is the 
fact that the evidence as to climatic pulsations in historic 
times indicates that regions along this path, for instance 
Greenland, the North Sea region, and southern Scandi- 

Fig. 3. Relative rainfall at times of increasing and decreasing 

HesT? shading, more lain with increaaing spots. Light shading, mors rain with d*- 
creasing spots. No data for unshaded areas. 

Figures indicate percentagee of the average rainfall by which the rainfall during 
periods of increasing spots exceeds or falls short of rainfeJl during periods of decreas- 
ing spots. The excess or deficiency is stated in percentagee of the average. Tfaiinfali 
data from Walker : Snnspots and Bain fall. 

. Relative rainfaU at times of increasing and decreasing 

Heavy shading, more rain with increasiiig spots. Light shading, moie rain with de- 
creasing spota. No data for nnshaded areas. 

FigDrea indicate percentagss of the average rainfall by which the rainfall during 
periods of increasing spots exceeds or falls short of rainf all during periods of decreas- 
ing spots. The excess or deflcienej is stated in percentages of the average. Bainfall 
data from Walker: Bonspots and BaJnfall. 


navia, were visited by especially frequent and severe 
storms at the climax of each pulsation. Moreover, the 
greatest accumulations of ice in the glacial period were 
on the poleward border of the general regions where now 
the storms appear to increase most at times of solar 

Even more clear is the evidence from other regions 
where storms increase at times of many sunspots. One 
such region includes the southwestern United States, 
while another is the Mediterranean region and the semi- 
arid or desert parts of Asia farther east. In these regions 
innumerable ruins and other lines of evidence show that 
at the climax of each climatic pulsation there was more 
storminess and rainfall than at present, just as there 
now is when the sun is most active. In still earlier times, 
while ice was accumulating farther north, the basins of 
these semi-arid regions were filled with lakes whose 
strands still remain to tell the tale of much-increased 
rainfall and presumable storminess. If we go back still 
further in geological times to the Permian glaciation, the 
areas where ice accumulated most abundantly appear to 
be the regions where tropical hurricanes produce the 
greatest rainfall and the greatest lowering of tempera- 
ture at times of many sunspots. From these and many 
other lines of evidence it seems probable that historic 
pulsations and glacial fluctuations are nothing more than 
sunspot cycles on a large scale. It is one of the funda- 
mental rules of science to reason from the known to the 
unknown, from the near to the far, from the present to 
the past. Hence it seems advisable to investigate whether 
any of the climatic phenomena of the past may have 
arisen from an intensification of the solar conditions 
which now appear to give rise to similar phenomena on 
a small scale. 


The rest ef this chapter will be devoted to a resume 
of certain tentative conclusions which have no bearing 
on the main part of this book, but which apply to the 
closing chapters. There we shall inquire into the perio- 
dicity of the climatic phenomena of geological times, and 
shall ask whether there is any reason to suppose that the 
sun's activity has exhibited similar periodicity. This 
leads to an investigation of the possible causes of dis- 
turbances in the sun's atmosphere. It is generally as- 
sumed that sunspots, solar prominences, the bright clouds 
known as faculae, and other phenomena denoting a per- 
turbed state of the solar atmosphere, are due to some 
cause within the sun. Yet the limitation of these phe- 
nomena, especially the sunspots, to restricted latitudes, 
as has been shown in Earth and Sun, does not seem to be 
in harmony with an internal solar origin, even though 
a banded arrangement may be normal for a rotating 
globe. The fairly regular periodicity of the sunspots 
seems equally out of harmony with an internal origin. 
Again, the solar atmosphere has two kinds of circula- 
tion, one the so-called **rice grains,'' and the other 
the spots and their attendant phenomena. Now the rice 
grains present the appearance that would be expected in 
an atmospheric circulation arising from the loss of heat 
by the outer part of a gaseous body like the sun. For 
these reasons and others numerous good thinkers from 
Wolf to Schuster have held that sunspots owe their 
periodicity to causes outside the sun. The only possible 
cause seems to be the planets, acting either through 
gravitation, through forces of an electrical origin, or 
through some other agency. Various new investigations 
which are describied in Earth and Sun support this con- 
clusion. The chief difficulty in accepting it hitherto has 
been that although Jupiter, because of its size, would be 


expected to dominate the sunspot cycle, its period of 
11.86 years has not been detected. The sunspot cycle has 
appeared to average 11.2 years in length, and has been 
called the 11-year cycle. Nevertheless, a new analysis of 
the sunspot data shows that when attention is concen- 
trated upon the major maxima, which are least subject to 
retardation or acceleration by other causes, a periodicity 
closely approaching that of Jupiter is evident. Moreover, 
when the effects of Jupiter, Saturn, and the other planets 
are combined, they produce a highly variable curve which 
has an extraordinary resemblance to the sunspot curve. 
The method by which the planets influence the sun's 
atmosphere is still open to question. It may be through 
tides, through the direct effect of gravitation, through 
electro-magnetic forces, or in some other way. Whichever 
it may be, the result may perhaps be slight differences of 
atmospheric pressure upon the sun. Such differences 
may set in motion slight whirling movements analogous 
to terrestrial storms, and these presumably gather mo- 
mentum from the sun's own energy. Since the planet- 
ary influences vary in strength because of the continuous 
change in the relative distances and positions of the 
planets, the sun's atmosphere appears to be swayed by 
cyclonic disturbances of varying degrees of severity. The 
cyclonic disturbances known as sunspots have been 
proved by Hale to become more highly electrified as they 
increase in intensity. At the same time hot gases pre- 
sumably well up from the lower parts of the solar atmos- 
phere and thereby cause the sim to emit more heat. Thus 
by one means or another, the earth's atmosphere appears 
to be set in commotion and cycles of climate are in- 

If the preceding reasoning is correct, any disturbance 
of the solar atmosphere must have an effect upon the 


earth's climate. If the disturbance were great enough and 
of the right nature it might produce a glacial epoch. The 
planets are by no means the only bodies which act upon 
the sun, for that body sustains a constantly changing 
relation to millions of other celestial bodies of all sizes 
up to vast universes, and at all sorts of distances. If the 
sun and another star should approach near enough to one 
another, it is certain that the solar atmosphere would be 
disturbed much more than at present. 

Here we must leave the cyclonic hypothesis of climate 
and must refer the reader once more to Earth and Sun 
for fuller details. In the rest of this book we shall discuss 
the nature of the climatic changes of past times and shall 
inquire into their relation to the various climatic hypothe- 
ses mentioned in the last two chapters. Then we shall 
inquire into the possibility that the solar system has ever 
been near enough to any of the stars to cause appreciable 
disturbances of the solar atmosphere. We shall complete 
our study by investigating the vexed question of why 
movements of the earth's crust, such as the uplifting of 
continents and moimtain chains, have generally occurred 
at the same time as great climatic fluctuations. This 
would not be so surprising were it not that the climatic 
phenomena appear to have consisted of highly complex 
cycles while the uplift has been a relatively steady move- 
ment in one direction. We shall find some evidence that 
the solar disturbances which seem to cause climatic 
changes also have a relation to movements of the crust. 


WE are now prepared to consider the climate of 
the past. The first period to claim attention is 
the few thousand years covered by written 
history. Strangely enough, the conditions during this 
time are known with less accuracy than are those of 
geological periods hundreds of times more remote. Yet 
if pronounced changes have occurred since the days of 
the ancient Babylonians and since the last of the post- 
glacial stages, they are of great importance not only 
because of their possible historic effects, but because they 
bridge the gap* between the little variations of climate 
which are observable during a single lifetime and the 
great changes known as glacial epochs. Only by bridging 
the gap can we determine whether there is any genetic 
relation between the great changes and the small. A full 
discussion of the climate of historic times is not here 
advisable, for it has been considered in detail in numer- 
ous other publications.^ Our most profitable course would 
seem to be to consider first the general trend of opinion 
and then to take up the chief objections to each of the 
main hypotheses. 
In the hot debate over this problem during recent 

iMuch of this chapter is taken from The Solar Hypothesis of dimatie 
Changes; Bull. Geol. Soc. Am., Vol. 25, 1914. 

> Ellsworth Huntington: Explorations in Turkestan, 1905; The Pulse of 
Asia, 1907; Palestine and Its Transformation, 1911; The Climatic Factor, 
1915; World Power and Evolution, 1919. 


decades the ideas of geographers seem to have gone 
through much the same metamorphosis as have those of 
geologists in regard to the climate of far earlier times. 

As every geologist well knows, at the dawn of geology 
people believed in climatic uniformity — that is, it was 
supposed that since the completion of an original creative 
act there had been no important changes. This view 
quickly disappeared and was superseded by the hypothe- 
sis of progressive cooling and drying, an hypothesis 
which had much to do with the development of the nebu- 
lar hypothesis, and which has in turn been greatly 
strengthened by that hypothesis. The discovery of evi- 
dence of widespread continental glaciation, however, 
necessitated a modification of this view, and succeeding 
years have brought to light a constantly increasing num- 
ber of glacial, or at least cool, periods distributed 
throughout almost the whole of geological time. More- 
over, each year, almost, brings new evidence of the great 
complexity of glacial periods, epochs, and stages. Thus, 
for many decades, geologists have more and more been 
led to believe that in spite of surprising uniformity, when 
viewed in comparison with the cosmic possibilities, the 
climate of the past has been highly unstable from the 
viewpoint of organic evolution, and its changes have been 
of all degrees of intensity. 

Geographers have lately been debating the reality of 
historic changes of climate in the same way in which 
geologists debated the reality of glacial epochs and 
stages. Several hypotheses present themselves but these 
may all be grouped under three headings; namely, the 
hypotheses of (1) progressive desiccation, (2) climatic 
uniformity, and (3) pulsations. The hypothesis of pro- 
gressive desiccation has been widely advocated. In many 
of the drier portions of the world, especially between 30° 


and 40° from the equator, and preeminently in western 
and central Asia and in the southwestern United States, 
almost innumerable facts seem to indicate that two or 
three thousand years ago the climate was distinctly 
moister than at present. The evidence includes old lake 
strands, the traces of desiccated springs, roads in places 
now too dry for caravans, other roads which make de- 
tours around dry lake beds where no lakes now exist, and 
fragments of dead forests extending over hundreds of 
square miles where trees cannot now grow for lack of 
water. Still stronger evidence is furnished by ancient 
ruins, hundreds of which are located in places which are 
now so dry that only the merest fraction of the former 
inhabitants could find water. The ruins of Pahnyra, in 
the Syrian Desert, show that it must once have been a 
city like modem Damascus, with one or two hundred 
thousand inhabitants, but its water supply now suffices 
for only one or two thousand. All attempts to increase the 
water supply have had only a slight effect and the water 
is notoriously sulphurous, whereas in the former days, 
when it was abundant, it was renowned for its excellence. 
Hundreds of pages might be devoted to describing simi- 
lar ruins. Some of them are even more remarkable for 
their dryness than is Niya, a site in the Tarim Desert of 
Chinese Turkestan. Yet there the evidence of desiccation 
within 2000 years is so strong that even so careful and 
conservative a man as Hann,' pronounces it **uber- 
zeugend. ' ' 

A single quotation from scores that might be used will 
iUustratfe the conclusions of some of the most careful 

s J. Hann: Klimatologie, Vol. 1, 1908, p. 352. 

« H. C. Butler: Desert S^ia, the Land of a Lost GiTOization; Qeographi- 
cal Review, Feb., 1920, pp. 77-108. 


Among the regions which were once popnious and highly 
civilized, bnt which are now desert and deserted, there are few 
which were more closely connected with the beginnings of our 
own civilization than the desert parts of Syria and northern 
Arabia. It is only of recent years that the vast extent and great 
importance of this lost civilization has been f nlly recognized and 
that attempts have been made to reduce the extent of the unex- 
plored area and to discover how much of the territory which has 
long been known as desert was formerly habitable and inhabited. 
The results of the explorations of the last twenty years have been 
most astonishing in this regard. It has been found that practi- 
cally all of the wide area lying between the coast range of the 
eastern Mediterranean and the Euphrates, appearing upon the 
maps as the Syrian Desert, an area embracing somewhat more 
than 20,000 square miles, was more thickly populated than any 
area of similar dimensions in England or in the United States 
is today if one excludes the immediate vicinity of the large 
modem cities. It has also been discovered that an enormous 
desert tract lying to the east of Palestine, stretching eastward 
and southward into the country which we know as Arabia, was 
also a densely populated country. How far these settled regions 
extended in antiquity is still unknown, but the most distant 
explorations in these directions have failed to reach the end of 
ruins and other signs of former occupation. 

The traveler who has crossed the settled, and more or less 
populous, coast range of northern Syria and descended into the 
narrow fertile valley of the Orontes, encounters in any farther 
journey toward the east an irregular range of limestone hills 
lying north and south and stretching to the northeast almost 
halfway to the Euphrates. These hills are about 2,500 feet high, 
rising in occasional peaks from 3,000 to 3,500 feet above sea level. 
They are gray and unrelieved by any visible vegetation. On 
ascending into the hills the traveler is astonished to find at every 
turn remnants of the work of men's hands, paved roads, walls 
which divided fields, terrace walls of massive structure. Pres- 
ently he comes upon a small deserted and partly ruined town 


composed of buildings large and small constructed of beauti- 
fully wrought blocks of limestone, all rising out of the barren 
rock which forms the ribs of the hills. If he mounts an eminence 
in the vicinity, he will be still further astonished to behold 
similar ruins lying in all directions. He may count ten or fifteen 
or twenty, according to the commanding position of his lookout. 
From a distance it is often difficult to belieTC that these are not 
inhabited places; but closer inspection reveals that the gentle 
hand of time or the rude touch of earthquake has been laid upon 
every building. Some of the towns are better preserved than 
others; some buildings are quite perfect but for their wooden 
roofs which time has removed, others stand in picturesque ruins, 
while others still are level with the ground. On a far-off hilltop 
stands the ruin of a pagan temple, and crowning some lofty ridge 
lie the ruins of a great Christian monastery. Mile after mile of 
this barren gray country may be traversed without encountering 
a single human being. Day after day may be spent in traveling 
from one ruined town to another without seeing any g^reen 
thing save a terebinth tree or two standing among the ruins, 
which have sent their roots down into earth still preserved in 
the foundations of some ancient building. No soil is visible 
anywhere except in a few pockets in the rock from which it 
could not be washed by the torrential rains of the wet season; 
yet every ruin is surrounded with the remains of presses for the 
making of oil and wine. Only one oasis has been discovered in 
these high plateaus. 

Passing eastward from this range of hills, one descends into a 
gently rolling country that stretches miles away toward the 
Euphrates. At the eastern foot of the hills one finds oneself in a 
totally different country, at first quite fertile and dotted with 
frequent villages of flat-roofed houses. Here practically all the 
remains of ancient times have been destroyed through ages of 
building and rebuilding. Beyond this narrow fertile strip the 
soil grows drier and more barren, until presently another kind 
of desert is reached, an undulating waste of dead soil. Few walls 
or towers or arches rise to break the monotony of the unbroken 


landscape ; but the earef ul explorer will find on closer examina- 
tion that this region was more thickly populated in antiquity 
even than the hill country to the west. Every unevenness of the 
surface marks the site of a town^ some of them cities of con- 
siderable extent. 

We may draw certain very definite conclusions as to the 
former conditions of the country itself. There was soil upon the 
northern hills where none now exists, for the buildings now show 
unfinished foundation courses which were not intended to be 
seen; the soil in depressions without outlets is deeper than it 
formerly was; there are hundreds of olive and wine presses in 
localities where no tree or vine could now find footing; and 
there are hillsides with ruined terrace walls rising one above 
the other with no sign of earth near them. There was also a large 
natural water supply. In the north as well as in the south we 
find the dry beds of rivers^ streams, and brooks with sand and 
pebbles and well-worn rocks but no water in them from one 
year's end to the other. We find bridges over these dry streams 
and crudely made washing boards along their banks directly 
below deserted towns. Many of the bridges span the beds of 
streams that seldom or never have water in them and give 
clear evidence of the great climatic changes that have taken 
place. There are well heads and well houses, and inscriptions 
referring to springs; but neither wells nor springs exist today 
except in the rarest instances. Many of the houses had their 
rock-hewn cisterns, never large enough to have supplied water 
for more than a brief period, and corresponding to the cisterns 
which most of our recent forefathers had which were for con- 
venience rather than for dependence. Some of the towns in 
southern Syria were provided with large public reservoirs, but 
these are not large enough to have supplied water to their 
original populations. The high plateaus were of course without 
irrigation; but there are no signs, even in the lower flatter 
country, that irrigation was ever practiced ; and canals for this 
purpose could not have completely disappeared. There were 
forests in the immediate vicinity, forests producing timbers of 
great length and thickness ; for in the north and northeast prac- 


tically all the buildings had wooden roofs, wooden intermediate 
floors, and other features of wood. Costly buildings, such as 
temples and churches, employed large wooden beams; but wood 
was used in much larger quantities in private dwellings, shops, 
stables, and barns. If wood had not been plentiful and cheap — 
which means grown near by — ^the builders would have adopted 
the building methods of their neighbors in the south, who used 
very little wood and developed the most perfect type of lithic 
architecture the world has ever seen. And here there exists a 
strange anomaly: Northern Syria, where so much wood was 
employed in antiquity, is absolutely treeless now; while in the 
mountains of southern Syria, where wood must have been 
scarce in antiquity to have forced upon the inhabitants an almost 
exclusive use of stone, there are still groves of scrub oak and 
pine, and travelers of half a century ago reported large forests 
of chestnut trees." It is perfectly apparent that large parts of 
Syria once had soil and forests and springs and rivers, while it 
has none of these now, and that it had a much larger and better 
distributed rainfall in ancient times than it has now. 

Professor Butler *s careful work is especially interest- 
ing because of its contrast to the loose statements of 
those who believe in climatic uniformity. So far as I am 
aware, no opponent of the hypothesis of climatic changes 
has ever even attempted to show by careful statistical 
analysis that the ancient water supply of such ruins w^as 
no greater than that of the present. The most that has 
been done is to suggest that there may have been sources 
of water which are now unknown. Of course, this might 
be true in a single instance, but it could scarcely be the 
case in many hundreds or thousands of ruins. 

B This is due to the fact that where these forests occur, in Gilead for 
example, the mountains to the west break down, so that the west winds with 
water from the Mediterranean are able to reach the inner range without 
having lost all their water. It is one of the misfortunes of Syria that its 
mountains generally rise so close to the sea that they shut off rainfall from 
the interior and cause the rain to fall on slopes too steep for easy cultivation. 


Although the arguments in favor of a change of cli- 
mate during the last two thousand years seem too strong 
to be ignored, their very strength seems to have been a 
source of error. A large number of people have jumped 
to the conclusion that the change which appears to have 
occurred in certain regions occurred everywhere, and 
that it consisted of a gradual desiccation. 

Many observers, quite as careful as those who believe 
in progressive desiccation, point to evidences of aridity 
in past times in the very regions where the others find 
proof of moisture. Lakes such as the Caspian Sea fell to 
such a low level that parts of their present floors were 
exposed and were used as sites for buildings whose ruins 
are still extant. Elsewhere, for instance in the Tian-Shan 
Mountains, irrigation ditches are found in places where 
irrigation never seems to be necessary at present. In 
SyiS and North Africa during the early centuries of the 
Christian era the Eomans showed unparalleled activity 
in building great aqueducts and in watering land which 
then apparently needed water almost as much as it does 
today. Evidence of this sort is abundant and is as con- 
vincing as is the evidence of moister conditions in the 
past It is admirably set forth, for example, in the com- 
prehensive and ably written monograph of Leiter on the 
climate of North Africa.* The evidence cited there and 
elsewhere has led many authors strongly to advocate the 
hypothesis of climatic uniformity. They have done ex- 
actly as have the advocates of progressive change, and 
have extended their conclusions over the whole world and 
over the whole of historic times. 

The hypotheses of climatic uniformity and of progres- 

• U. Leiter: Die Frage der Klimaanderang waherend geBchiehtlicher Zeit 
in Nordafrika. Abhandl. K. K. Geographischen G^esellschaft, Wien, 1909^ 
p. 143. 


sive change both seem to be based on reliable evidence. 
They may seem to be diametrically opposed to one 
another, but this is only when there is a failure to group 
the various lines of evidence according to their dates, and 
according to the types of climate in which they happen 
to be located. When the facts are properly grouped in 
both time and space, it appears that evidence of moist 
conditions in the historic Mediterranean lands is found 
during certain periods ; for instance, four or five hundred 
years before Christ, at the time of Christ, and 1000 A. D- 
The other kind of evidence, on the contrary, culminates 
at other epochs, such as about 1200 B. C. and in the 
seventh and thirteenth centuries after Christ. It is also 
found during the interval from the culmination of a moist 
epoch to the culmination of a dry one, for at such times 
the climate was growing drier and the people were under 
stress. This was seemingly the case during the period 
from the second to the fourth centuries of our era. North 
Africa and Syria must then have been distinctly better 
watered than at present, as appears from Butler's vivid 
description ; but they were gradually becoming drier, and 
the natural effect on a vigorous, competent people like the 
Bomans was to cause them to construct numerous engi- 
neering works to provide the necessary water. 

The considerations which have just been set forth have 
led to a third hypothesis, that of pulsatory climatic 
changes. According to this, the earth's climate is not 
stable, nor does it change uniformly in one direction. It 
appears to fluctuate back and forth not only in the little 
waves which we see from year to year or decade to 
decade, but in much larger waves, which take hundreds of 
years or even a thousand. These in turn seem to merge 
into and be imposed on the greater waves which form 
glacial stages, glacial epochs, and glacial periods. At the 


present time there seems to be no way of determining 
whether the general tendency is toward aridity or toward 
glaciation. The seventh century of our era was appar- 
ently the driest time during the historic period — distinctly 
drier than the present — ^but the thiri;eenth century was 
almost equally dry, and the twelfth or thirteenth before 
Christ may have been very dry. 

The best test of an hypothesis is actual measurements. 
In the case of the pulsatory hypothesis we are fortu- 
nately able to apply this test by means of trees. The 
growth of vegetation depends on many factors — soil, ex- 
posure, wind, sun, temperature, rain, and so forth. In a 
dry region the most critical factor in determining how a 
tree ^s growth shall vary from year to year is the supply 
of moisture during the few months of most rapid 
growth.^ The work of Douglass® and others has shown 
that in Arizona and California the thickness of the 
annual rings affords a reliable indication of the amount 
of moisture available during the period of growth. This 
is especially true when the growth of several years is 
taken as the unit and is compared with the growth of 
a similar number of years before or after. Where a long 
series of years is used, it is necessary to make corrections 
to eliminate the effects of age, but this can be done by 
mathematical methods of considerable accuracy. It is 
difficult to determine whether the climate at the beginning 

tA moet earefal and conyincing study of this problem is embodied in 
an article hj J. W. Smith : The Effects of Weather upon the Yield of Com ; 
Monthly Weather Beview, Vol. 42, 1914, pp. 78-92. On the basis of the 
yield of com in Ohio for 60 years and in other states for shorter periods, 
he shoivs that the rainfall of July has almost as much influence on the crop 
as has the rainfall of all other months combined. See his Agricultural 
Meteorology, New York, 1920. 

8 See chapter by A. E. Douglass in The Climatic Factor ; and his book on 
Climatic Cycles and Tree-Growth; Carnegie Inst., 1919. Also article by 
M. N. Stewart: The Belation of Precipitation to Tree Growth, in the 
Monthly Weather Review, Vol. 41, 1913. 


and end of a tree 's life was the same, but it is easily pos- 
sible to determine whether there have been pulsations 
while the tree was making its growth. If a large number 
of trees from various parts of a given district all formed 
thick rings at a certain period and then formed thin ones 
for a hundred years, after which the rings again become 
thick, we seem to be safe in concluding that the trees have 
lived through a long, dry period. The full reasons for this 
belief and details as to the methods of estimating climate 
from tree growth are given in The Climatic Factor. 

The results set forth in that volume may be summa- 
rized as follows : During the years 1911 and 1912, under 
the auspices of the Carnegie Institution of Washington, 
measurements were made of the thickness of the rings of 
growth on the stumps of about 450 sequoia trees in Cali- 
fornia. These trees varied in age from 250 to nearly 
3250 years. The great majority were over 1000 years of 
age, seventy-nine were over 2000 years, and three over 
3000. Even where only a few trees are available the 
record is surprisingly reliable, except where occasional 
accidents occur. Where the number approximates 100, 
accidental variations are largely eliminated and we may 
accept the record with considerable confidence. Accord- 
ingly, we may say that in California we have a fairly 
accurate record of the climate for 2000 years and an 
approximate record for 1000 years more. The final re- 
sults of the measurements of the California trees are 
shown in Fig. 4, where the climatic variations for 3000 
years in California are indicated by the soUd line. The 
high parts of the line indicate rainy conditions, the low 
parts, dry. Aji examimation of this curve shows that 
during 3000 years there have apparently been climatic 
variations more important than any which have taken 
place during the past century. In order to bring out the 


















9 A 



■^ .S 





details more clearly, the more reliable part of the Cali- 
fornia curve, from 100 B. C. to the present time, has been 
reproduced in Fig. 5. This is identical with the corre- 
sponding part of Fig. 4, except that the vertical scale is 
three times as great. 

The curve of tree growth in California seems to be a 
true representation of the general features of climatic 
pulsations in the Mediterranean region. This conclusion 
was originally based on the resemblance between the 
solid line of Fig. 4, representing tree growth, and the 
dotted line representing changes of climate in the eastern 
Mediterranean region as inferred from the study of ruins 
and of history before any work on this subject had been 
done in America.* The dotted line is here reproduced for 
its historical significance as a stage in the study of cli- 
matic changes. If it were to be redrawn today on the 
basis of the knowledge acquired in the last twelve years, 
it would be much more like the tree curve. For example, 
the period of aridity suggested by the dip of the dotted 
line about 300 A. D. was based largely on Professor 
Butler's data as to the paucity of inscriptions and ruins 
dating from that period in Syria. In the recent article, 
from which a long quotation has been given, he shows 
that later work proves that there is no such paucity. On 
the other hand, it has accentuated the marked and sudden 
decay in civilization and population which occurred 
shortly after 600 A. D. He reached the same conclusion 
to which the present authors had come on wholly different 
grounds, namely, that the dip in the dotted line about 300 
A. D. is not warranted, whereas the dip about 630 A. D. 
is extremely important. In similar fashion the work of 

9 The dotted line is taken from Palestine and Its Transformation, pp. 
327 and 403. 

































"S o g 


53 -^J .*a 


© -^ 'd 

S 9 S 

CO jQ 

« «8 Q 

»o i " 




^ M k> 


be ■ 


Stein^^ in central Asia makes it clear that the contrast 
between the water supply about 200 B. C. and in the pre- 
ceding and following centuries was greater than was 
supposed on the basis of the scanty evidence available 
when the dotted line of Pig. 4 was drawn in 1910. 

Since the curve^ of the California trees is the only con- 
tinuous and detailed record yet available for the climate 
of the last three thousand years, it deserves most careful 
study. It is especially necessary to determine the degree 
of accuracy with which the growth of the trees repre- 
sents (1) the local rainfall and (2) the rainfall of remote 
regions such as Palestine. Perhaps the best way to deter- 
mine these matters is the standard mathematical method 
of correlation coefficients. If two phenomena vary in 
perfect unison, as in the case of the turning of the wheels 
and the progress of an automobile when the brakes are 
not applied, the correlation coefficient is 1.00, being posi- 
tive when the automobile goes forward and negative 
when it goes backward. If there is no relation between 
two phenomena, as in the case of the number of miles run 
by a given automobile each year and the number of 
chickens hatched in the same period, the coefficient is 
zero. A partial relationship where other factors enter 
into the matter is represented by a coefficient between 
zero and one, as in the case of the movement of the auto- 
mobile and the consumption of gasoline. In this case the 
relation is very obvious, but is modified by other factors, 
including the roughness and grade of the road, the 
amount of traffic, the number of stops, the skill of the 
driver, the condition and load of the automobile, and the 
state of the weather. Such partial relationships are the 
kind for which correlation coefficients are most useful, 
for the size of the coefficients shows the relative im- 

to M. A. Stein : Bains of Desert Cathajr, London, 1912. 


portance of the various factors. A correlation coefiScient 
four times the probable error, which can always be deter- 
mined by a formula well known to mathematicians, is 
generally considered to afford evidence of some kind of 
relation between two phenomena. When the ratio between 
coefficient and error rises to six, the relationship is re- 
garded as strong. 

Few people would question that there is a connection 
between tree growth and rainfall, especially in a climate 
with a long summer dry season like that of OaUfomia. 
But the growth of the trees also depends on their posi- 
tiojuJ^e-wnount of shading, the temperature, insect pests, 
blights, the wind with its tendency to break the branches, 
and a number of other factors. Moreover, while rain 
commonly favors growth, great extremes are relatively 
less helpful than more moderate amounts. Again, the 
roots of a tree may tap such deep sources of water that 
neither drought nor excessive rain produces much effect 
for several years. Hence in comparing the growth of the 
huge sequoias with the rainfall we should expect a corre- 
lation coefficient high enough to be convincing, but de- 
cidedly below 1.00. Unfortunately there is no record of 
the rainfall where the sequoias grow, the nearest long 
record being that of Sacramento, nearly 200 miles to the 
northwest and close to sea level instead of at an altitude 
of about 6000 feet. 

Applying the method of correlation coefficients to the 
annual rainfall of Sacramento and the growth of the 
sequoias from 1863 to 1910, we obtain the results shown 
in Table 3. The trees of Section A of the table grew in 
moderately dry locations although the soil was fairly 
deep, a condition which seems to be essential to sequoias. 
In this case, as in all the others, the rainfall is reckoned 
from July to June, which practically means from October 




A. Sacbamkmto Rainfall and Obowth ot 18 Skquoias in Dbt 

Locations, 1861-1910 

(r) («) W 

1 year of rainfall —0.059 ±0.096 0.6 

2 years of rainfall -|-0.288 ±0.090 3.2 

3 years of rainfall +0.570 ±0.066 8.7 

4 years of rainfall +0.470 ±0.076 6.2 

B. Sacramento Baixpall and Growth of 112 Sequoias Mostly in 

Moist Locations, 1861-1910 

3 years of rainfall +0.340 ±0.087 3.9 

4 years of rainfall +0.371 ±0.084 4.6 

5 years of rainfall +0.398 ±0.082 4.9 

6 years of rainfall +^-*18 ±0.079 5.3 

7 years of rainfall +0.471 ±0.076 6.2 

8 years of rainfall (+0.520) ±0.071 7.3 

9 years of rainfall +0.575 ±0.065 8.8 

10 years of rainfall +0.577 ±0.065 8.8 

C. Sacramento Rainfall and Growth of 80 Sequoias in Moist 

Locations, 1861-1910 

10 years of rainfall +0.605 ±0.062 9.8 

D. Annual Sequoia Growth and Bainfall of Precsdino 5 Years 
AT Stations on Southern Pacific Railroad 

2 -2^ >^ 111^ ell lie ^il 

(r) (e) W 

Sacramento, 1861-1910 70 19.40 200 +0.398 ±0.081 4.9 

Colfax, rl871-1909 2400 48.94 200 +0.122 ±0.113 1.1 

Summit, 1871-1909 7000 48.07 200 +0.148 ±0.113 1.3 

Truckee, 1871-1909 5800 27.12 200 +0.300 ±0.105 2.9 

Boca, 1871-1909 5500 20.34 200 +0,604. ±0.076 8.0 

Winnemncca, 1871-1909 4300 8.65 300 +0.492 ±0.089 5.5 

11 In the preparation and interpretation of this table the help of Mr. 
G. B. Cressey is gratefully acknowledged. 


to May, since there is almost no summer rain. Thus the 
tree growth in 1861 is compared with the rainfall of the 
preceding rainy season, 1860-1861, or of several preced- 
ing rainy seasons as the table indicates. 

In the first line of Section A a correlation coefficient 
of only — 0.056, which is scarcely six>tenths of the prob- 
able error, means that there is no appreciable relation 
between the rainfall of a given season and the growth 
dnring the following spring and summer. The roots of 
the sequoias probably penetrate so deeply that the rain 
and melted snow of the spring months do not sink down 
rapidly enough to influence the trees before the growing 
season comes to an end. The precipitation of two pre- 
ceding seasons, however, has some effect on the trees, as 
appears in the second line of Section A, where the corre- 
lation coefficient is +0.288, or 3.2 times the probable 
error. When the rainfall of three seasons is taken into 
account the coefficient rises to +0.570, or 8.7 times the 
probable error, while with four years of rainfall the coeffi- 
cient begins to fall off. Thus the growth of these eighteen 
sequoias on relatively dry slopes appears to have de- 
pended chiefly on the rainfall of the second and third 
preceding rainy seasons. The growth in 1900, for 
example, depended largely on the rainfall in the rainy 
seasons of 1897-1898 and 1898-1899. 

Section B of the table shows that with 112 trees, grow- 
ing chiefly in moist depressions where the water supply 
is at a maximum, the correlation between growth and 
rainfall, +0.577 for ten years' rainfall, is even higher 
than with the dry trees. The seepage of the underground 
water is so slow that not until four years' rainfall is 
taken into account is the correlation coefficient more than 
four times the probable error. When only the trees grow- 
ing in moist locations are employed, the coefficient be- 


tween tree growth and the rainfall for ten years rises to 
the high figure of +0.605, or 9.8 times the probable error, 
as appears in Section C. These figures, as weU as many 
others not here published, make it clear that the curve of 
sequoia growth from 1861 to 1910 affords a fairly close 
indication of the rainfall at Sacramento, provided allow- 
ance be made for a delay of three to ten years due to the 
fact that the moisture in the soil gradually seeps down 
the mountain-sides and only reaches the sequoias after a 
considerable interval. 

If a rainfall record were available for the place where 
the trees actually grow, the relationship would probably 
be still closer. 

The record at Fresno, for example, bears out this con- 
clusion so far as it goes. But as Fresno lies at a low alti- 
tude and its rainfall is of essentially the Sacramento 
type, its short record is of less value than that of Sacra- 
mento. The only rainfall records among the Sierras at 
high levels, where the rainfall and temperature are ap- 
proximately like those of the sequoia region, are found 
along the main line of the Southern Pacific railroad. This 
runs from Oakland northeastward seventy miles across 
the open plain to Sacramento, then another seventy miles, 
as the crow flies, through Colfax and over a high pass 
in the Sierras at Summit, next twenty miles or so down 
through Truckee to Boca, on the edge of the inland basin 
of Nevada, and on northeastward another 160 miles to 
Winnemucca, where it turns east toward Ogden and Salt 
Lake City. Section D of Table 3 shows the correlation 
coefScients between the rainfall along the railroad and 
the growth of the sequoias. At Sacramento, which lies 
fairly open to winds from the Pacific and thus represents 
the general climate of central California, the coefficient 
is nearly five times the probable error, thus indicating a 


real relation to sequoia growth. Then among the foothills 
of the Sierras at Colfax, the coefficient drops till it is 
scarcely larger than the probable error. It rises rapidly, 
however, as one advances among the mountains, until at 
Boca it attains the high figure of +0.604 or eight times 
the probable error, and continues high in the dry area 
farther east. In other words the growth of the sequoias 
is a good indication of the rainfall where the trees grow 
and in the dry region farther east 

In order to determine the degree to which the sequoia 
record represents the rainfall of other regions, let us 
select Jerusalem for comparison. The reasons for this 
selection are that Jerusalem furnishes the only available 
record that satisfies the following necessary conditions : 
(1) its record is long enough to be important; (2) it is 
located fairly near the latitude of the sequoias, 32''N 
versus ST^'N; (3) it is located in a similar type of climate 
with winter rains and a long dry summer; (4) it lies well 
above sea level (2500 feet) and somewhat back from the 
seacoast, thus approximating although by no means 
duplicating the condition of the sequoias; and (5) it lies 
in a region where the evidence of cUmatic changes during 
historic times is strongest. The ideal place for comparison 
would be the valley in which grow the cedars of Lebanon. 
Those trees resemble the sequoias to an extraordinary 
degree, not only in their location, but in their great age. 
Some day it will be most interesting to compare the 
growth of these two famous groups of old trees. 

The correlation coefficients for the sequoia growth 
and the rainfall at Jerusalem are given in Section A, 
Table 4. They are so high and so consistent that they 
scarcely leave room for doubt that where a hundred or 
more sequoias are employed, as in Fig. 5, their curve of 
growth affords a good indication of the fluctuations of 

J- ^ 



A. Jkbusalbm Bainfall roB 3 Yiabs and Yasious (teoups of 


If 1 1 IIP 

OS Alt B3SS,« 

(r) (e) W 

11 trees measured by Douglass 4-0.453 ±0.078 5.8 

.80 trees, moist locations, Qroups lA, 

IIA, IIIA, VA +0.500 ±0.073 6.8 

101 trees, 69 in moist locations, 32 in 

dry, I, II, m +0.616 ±0.061 10.1 

112 trees, 80 in moist locations, 32 in 

dry, I, II, III, V +0.675 ±0.053 12.7 

B. Baintall at Jeeusalbm and at Stations in Galipoknu and 


4 S ytaT9 ^ 4 6 ytan » 

^ "tsS "S^ tiS 

3 • -sl xl -^l I 

II S 68 sill II silt 

(r) («) (r) W 

Sacramento, 70 1861-1910 +0.386 4.7 +0.352 4.2 

Colfax, 2400 1871-1909 +0.311 3.1 +0.308 3.0 

Summit, 7000 1871-1909 +0.099 0.9 +0.248 2.3 

Truckee, 5800 1871-1909 +0.229 2.2 +0.337 3.3 

•Boca, 5500 1871-1909 +0.482 6.4 +0.617 8.6 

Winnemucca, 4300 1871-1909 +^.235 2.2 \^0.2tQ 2.4 

San Bernardino, 1050 1871-1909 +0.275 2.7 +0.177 1.8 

C. Rainfall fob 3 Ysabs at Califoknia and Nevada Stations, 


Sl S85l 

(r) W 

Sacramento and San Bernardino +0.663 10.7 

San Bernardino and Winnemucca +^-^^^ ^-^ 

IS For the tree data used in these comparisons, see The Climatic Factor, 
p. 328, and A. E. Douglass: Climatic Cycles and Tree Growth, p. 123. 
• One year interx>olated. 


climate in western Asia. The high coefficient for the 
eleven trees measured by Douglass suggests that where 
the number of trees falls as low as ten, as in the part of 
Fig. 4 from 710 to 840 B. C, the relation between tree 
growth and rainfall is still close even when only one 
year 's growth is considered. Where the unit is ten years 
of growth, as in Figs. 4 and 5, the accuracy of the tree 
curve as a measure of rainfall is much greater than when 
a single year is used as in Table 4. When the unit is 
raised to thirty years, as in the smoothed part of Fig. 4 
previous to 240 B. C, even four trees, as from 960 to 
1070, probably give a fair approximation to the general 
changes in rainfall, while a single tree prior to 1110 B. C. 
gives a rough indication. 

Table 4 shows a peculiar feature in the fact that the 
correlations of Section A between tree growth and the 
rainfall of Jerusalem are decidedly higher than those 
between the rainfall in the two regions. Only at Sacra- 
mento and Boca are the rainfall coefficients high enough 
to be conclusive. This, however, is not surprising, for 
even between Sacramento and San Bernardino, only 400 
miles apart, the correlation coefficient for the rainfall 
by three-year periods is only 10.7 times the probable 
error, as appears in Section C of Table 4, while between 
San Bernardino and Winnemucca 500 miles away, the 
corresponding figure drops to 2.8. It must be remem- 
bered that in some respects the growth of the sequoias is 
a much better record of rainfall than are the records kept 
by man. The human record is based on the amount of 
water caught by a little gauge a few inches in diameter. 
Every gust of wind detracts from the accuracy of the 
record ; a mile away the rainfall may be double what it 
is at the gauge. Each sequoia, on the other hand, draws 
its moisture from an area thousands of times as large as 


a rain gauge. Moreover, the trees on which Figs. 4 and 5 
are based were scattered over an area fifty miles long 
and several hundred square miles in extent. Hence they 
represent the summation of the rainfall over an area 
millions of times as large as that of a rain gauge. This 
fact and the large correlation coefficients between sequoia 
growth and Jerusalem rainfall should be considered in 
connection with the fact that all the coefficients between 
the rainfall of California and Nevada and that of Jeru- 
salem are positive. K full records of the complete rainfall 
of California and Nevada on the one hand and of the 
eastern Mediterranean region on the other were available 
for a long period, they would probably agree closely. 

Just how widely the sequoias can be used as a measure 
of the climate of the past is not yet certain. In some 
regions, as will shortly be explained, the climatic changes 
seem to have been of an opposite character from those 
of California. In others the Californian or eastern Medi- 
terranean type of change seems sometimes to prevail but 
is not always evident. For example, at Malta the rainfall 
today shows a distinct relation to that of Jerusalem and 
to the growth of the sequoias. But the correlation coeffi- 
cient between the rainfall of eight-year periods at Naples, 
a little farther north, and the growth of the sequoias at 
the end of the periods is — 0.132, or only 1.4 times the 
probable error and much too small to be significant. This 
is in harmony with the fact that although Naples has 
summer droughts, they are not so pronounced as in Cali- 
fornia and Palestine, and the prevalence of storms is 
much greater. Jerusalem receives only 8 per cent of its 
rain in the seven months from April to October, and 
Sacramento 13, while Malta receives 31 per cent and 
Naples 43. Nevertheless, there is some evidence that in 
the past the climatic fluctuations of southern Italy fol- 


lowed nearly the same course as those of California and 
Palestine. This apparent discrepancy seems to be ex- 
plained by our previous conclusion that changes of cli- 
mate are due largely to a shifting of storm tracks. When 
sunspots are numerous the storms which now prevail in 
northern Italy seem to be shifted southward and traverse 
the Mediterranean to Palestine just as similar storms 
are shifted southward in the United States. This perhaps 
accounts for the agreement between the sequoia curve 
and the agricultural and social history of Rome from 
about 400 B. C. to 100 A. D., as explained in World Power 
and Evolution. For our present purposes, however, the 
main point is that since rainfall records have been kept 
the fluctuations of climate indicated by the growth of the 
sequoias have agreed closely with fluctuations in the 
rainfall of the eastern Mediterranean region. Presumably 
the same was true in the past. In that case, the sequoia 
curve not only is a good indication of climatic changes or 
pulsations in regions of similar climate, but may serve 
as a guide to coincident but different changes in regions 
of other types. 

An enormous body of other evidence points to the same 
conclusion. It indicates that while the average climate 
of the present is drier than that of the past in regions 
having the Mediterranean type of winter rains and 
summer droughts, there have been pronounced pulsations 
during historic times so that at certain times there has 
actually been greater aridity than at present. This, con- 
clusion is so important that it seems advisable to examine 
the only important arguments that have been raised 
against it, especially against the idea that the general 
rainfall of the eastern Mediterranean was greater in the 
historic past than at present. The first objection is the 
unquestionable fact that droughts and famines have 


occurred at periods which seem on other evidence to have 
been moister than the present. This argoment has been 
much used, but it seems to have little force. If the rain- 
fall of a given region averages thirty inches and varies 
from fifteen to forty-five, a famine will ensue if the rain- 
fall drops for a few years to the lower limit and does not 
rise much above twenty for a few years. If the climate of 
the place changes during the course of centuries, so that 
the rainfall averages only twenty inches, and ranges 
from seven to thirty-five, famine will again ensue if the 
rainfall remains near ten inches for a few years. The 
ravages of the first famine might be as bad as those of 
the second. They might even be worse, because when the 
rainfall is larger the population is likely to be greater 
and the distress due to scarcity of food would affect a 
larger number of people. Hence historic records of 
famines and droughts do not indicate that the climate 
was either drier or moister than at present. They merely 
show that at the time in question the climate was drier 
than the normal for that particular period. 

The second objection is that deserts existed in the past 
much as at present. This is not a real objection, however, 
for, as we shall see more fully, some parts of the world 
suffer one kind of change and others quite the opposite. 
Moreover, deserts have always existed, and when we talk 
of a change in their climate we merely mean that their 
boundaries have shifted. A concrete example of the mis- 
taken use of ancient dryness as proof of climatic uni- 
formity is illustrated by the march of Alexander from 
India to Mesopotamia. Hedin gives an excellent presen- 
tation of the case in the second volume of his Overland 
to India. He shows conclusively that Alexander's army 
suffered terribly from lack of water and provisions. This 
certainly proves that the climate was dry, but it by no 



means indicates that there has been no change from the 
past to the present. We do not know whether Alexander's 
march took place during an especially dry or an espe- 
cially wet year. In a desert region like Makran, in 
sonthem Persia and Beluchistan^ where the chief diffi- 
culties occurred, the rainfall varies greatly from year to 
year. We have no records from Makran, but the condi- 
tions there are closely similar to those of southern 
Arizona and New Mexico. In 1885 and 1905 the rainfall 
for five stations in that region was as follows : 

Mean rainfaU dur- 



ino period gince 



Tuma, Arizona, 




Phoenix, Arizona, 




Tucson, Arizona, 




Lordsburg, New Meadco, 




El Paso, Texas (on New 

Mexico border). 





These stations are distributed over an area nearly 500 
miles east and west. Manifestly a traveler who spent the 
year 1885 in that region would have had much more diffi- 
culty in finding water and forage than one who traveled 
in the same places in 1905. During 1885 the rainfall was 
42 per cent less than the average, and during 1905 it was 
134 per cent more than the average. Let us suppose, for 
the sake of argument, that the average rainfall of south- 
eastern Persia is six inches today and was ten inches in 
the days of Alexander. If the rainfall from year to year 
varied as much in the past in Persia as it does now in 
New Mexico and Arizona, the rainfall during an ancient 


dry year, corresponding in character to 1885, would have 
been about 5.75 inches. On the other hand, if we suppose 
that the rainfall then averaged less than at present, — ^let 
us say four inches, — a wet year corresponding to 1905 in 
the American deserts might have had a rainfall of about 
ten inches. This being the case, it is clear that our esti- 
mate of what Alexander's march shows as to climate 
must depend largely on whether 325 B. C. was a wet year 
or a dry year. Inasmuch as we know nothing about this, 
we must fall back on the fact that a large army accom- 
plished a journey in a place where today even a small 
caravan usually finds great difficulty in procuring forage 
and water. Moreover, elephants were taken 180 miles 
across what is now an ahnost waterless desert, and yet 
the old historians make no comment on such a feat which 
today would be practically impossible. These things seem 
more in harmony with a change of climate than with 
uniformity. Nevertheless, it is not safe to place much 
reliance on them except when they are taken in con- 
junction with other evidence, such as the numerous ruins, 
which show that Makran was once far more densely 
populated than now seems possible. Taken by itself, such 
incidents as AJexander's march cannot safely be used 
either as an argument for or against changes of climate. 
The third and strongest objection to any hypothesis 
of climatic changes during historic times is based on 
vegetation. The whole question is admirably set forth by 
J. W. Gregory," who gives not only his own results, but 
those of the ablest scholars who have preceded him. His 
conclusions are important because they represent one of 
the few cases where a definite statistical attempt has been 
made to prove the exact condition of the climate of the 

IS J. W. Gregory: Is the Earth Drying XTpf Geog. Jour., Vol. 43, 1914, 
pp. 148-172 and 293-318. 


past. After stating various less important reasons for 
believing that the climate of Palestine has not changed, 
he discusses vegetation. The following quotation indi- 
cates his line of thought. A sentence near the beginning 
is italicized in order to call attention to the importance 
which Gregory and others lay on this particular kind of 
evidence : 

Some more certain test is necessary than the general con- 
clusions which can be based upon the historical and geographical 
evidence of the Bible. In the absence of rain gauge and thermo- 
metric records, the most precise test of climate is given by the 
vegetation; and fortunately the palm affords a very delicate test 
of the past climate of Palestine and the eastern Mediterranean. 
• . . The date palm has three limits of growth which are deter- 
mined by temperature; thus it does not reach full maturity or 
produce ripe fruit of good quality below the mean annual tem- 
perature of 69°F. The isothermal of 69^ crosses southern Algeria 
near Biskra; it touches the northern coasts of Cyrenaica near 
Dema and passes Egypt near the mouth of the Nile, and then 
bends northward along the coast lands of Palestine. 

To the north of this line the date palm grows and produces 
fruit, which only ripens occasionally, and its quality deteriorates 
as the temperature falls below 69^. Between the isotherms of 
68^ and 64^, limits which include northern Algeria, most of 
Sicily, Malta, the southern parts of Greece and northern Syria, 
the dates produced are so unripe that they are not edible. In the 
next cooler zone, north of the isotherm of 62"", which enters 
Europe in southwestern Portugal, passes through Sardinia, 
enters Italy near Naples, crosses northern Greece and Asia 
Minor to the east of Smyrna, the date palm is grown only for 
its foliage, since it does not fruit. 

Hence at Benghazi, on the north African coast, the date palm 
is fertile, but produces fruit of poor quality. In Sicily and at 
Algiers the fruit ripens occasionally and at Rome and Nice the 
palm is grown only as an ornamental tree. 


The date palm therefore affords a test of variations in mean 
annual temperature of three grades between 62'' and 69^. 

This test shows that the mean annual temperature of Palestine 
has not altered since Old Testament times. The palm tree now 
grows dates on the coast of Palestine and in the deep depression 
around the Dead Sea^ but it does not produce fruit on the high- 
lands of Judea. Its distribution in ancient times, as far as we 
can judge from the Bible, was exactly the same. It grew at 
''Jericho, the city of palm trees" (Deut. xxxiv: 3 and 2 Chron. 
xxviii: 15), and at Engedi, on the western shore of the Dead 
Sea (2 Chron. xx:2; Sirach xxiy:14); and though the palm 
does not still live at Jericho — ^the last apparently died in 1838 — 
its disappearance must be due to neglect, for the only climatic 
change that would explain it would be an increase in cold or 
moisture. In olden times the date palm certainly grew on the 
highlands of Palestine; but apparently it never produced fruit 
there, for the Bible references to the palm are to its beauty and 
erect growth: "The righteous shall flourish like the palm" (Ps. 
xcii: 12) ; ''They are upright as the palm tree" (Jer. x: 5) ; 
"Thy stature is like to a palm tree" (Cant, vii: 7). It is used as 
a symbol of victory (Rev. vii: 9), but never praised as a source 
of food. 

Dates are not once referred to in the text of the Bible, but 
according to the marginal notes the word translated "honey" in 
2 Chron. xxxi : 5 may mean dates. . . . 

It appears, therefore, that the date palm had essentially the 
same distribution in Palestine in Old Testament times as it has 
now; and hence we may infer that the mean temperature was 
then the same as now. If the climate had been moister and cooler, 
the date could not have flourished at Jericho. If it had been 
warmer, the palms would have grown freely at higher levels and 
Jericho would not have held its distinction as the city of palm 

In the main Gregory's conclusions seem to be well 
grounded, although even according to his data a change 

1* Geog. Jour., Vol. 43, pp. 159161. 


of 2"* or 3° in mean temperature would be perfectly 
feasible. It will be noticed, however, that they apply to 
te mpera ture and not tojaiaf all. They merely prove that 
two thousand years ago the mean temperature of Pales- 
tine and the neighboring regions was not appreciably dif- 
ferent from what it is today. This, however, is in no sense 
out of harmony with the hypothesis of climatic pulsa- 
tions. Students of glaciation believe that during the last 
glacial epoch the mean temperature of the earth as a 
whole was only 5° or 6°C. lower than at present. If the 
difference between the climate of today and of the time of 
Christ is a tenth as great as the difference between the 
climate of today and that which prevailed at the culmina- 
tion of the last glacial epoch, the change in two thousand 
years has been of large dimensions. Yet this would re- 
quire a rise of only half a degree Centigrade in the mean 
temperature of Palestine. Manifestly, so slight a change 
would scarcely be detectable in the vegetation. 

The slightness of changes in mean temperature as com- 
pared with changes in rainfall may be judged from a 
comparison of wet and dry years in various regions. For 
example, at Berlin between 1866 and 1905 the ten most 
rainy years had an average precipitation of 670 mm. and 
a mean temperature of 9.15"* C. On the other hand, the ten 
years of least rainfall had an average of 483 mm. and a 
mean temperature of 9.35°. In other words, a difference 
of 137 mm., or 39 per cent, in rainfall was accompanied 
by a difference of only 0.2° C. in temperature. Such con- 
trasts between the variability of mean rainfall and mean 
temperature are observable not only when individual 
years are selected, but when much longer periods are 
taken. For instance, in the western Gulf region of the 
United States the two inland stations of Vicksburg, Mis- 
sissippi, and Shreveport, Louisiana, and the two mari- 


time stations of New Orleans, Louisiana, and Galveston, 
Texas, lie at the margins of an area about 400 miles long. 
During the ten years from 1875 to 1884 their rainfall 
averaged 59.4 inches," while during the ten years from 
1890 to 1899 it averaged only 42.4 inches. Even in a 
region so well watered as the Gulf States, such a change 
— 40 per cent more in the first decade than in the second 
— ^is important, and in drier regions it would have a great 
effect on habitability. Yet in spite of the magnitude of 
the change the mean temperature was not appreciably 
different, the average for the four stations being 67.36^F. 
during the more rainy decade and 66.94° F. during the 
less rainy decade — a difference of only 0.42**F. It is worth 
noticing that in this case the wetter period was also the 
warmer, whereas in Berlin it was the cooler. This is 
probably because a large part of the moisture of the Gulf 
States is brought by winds having a southerly com- 
ponent. Similar relationships are apparent in other 
places. We select Jerusalem because we have been dis- 
cussing Palestine. At the time of writing, the data avail- 
able in the Quarterly Journal of the Palestine Explora- 
tion Fund cover the years from 1882-1899 and 1903-1909. 
Among these twenty-five years the thirteen which had 
most rain had an average of 34.1 inches and a tempera- 
ture of 62.04°F. The twelve with least rain had 24.4 inches 
and a temperature of 62.44**. A difference of 40 per cent 
in rainfall was accompanied by a difference of only 
0.4'^F. in temperature. 

The facts set forth in the preceding paragraphs seem 
to show that extensive changes in precipitation and 
storminess can take place without appreciable changes of 
mean temperature. If such changed conditions can per- 
is See A. J. Henry : Secular Variation of Precipitation in the Unit«d 
States; Bull. Am. Geog. Soc., Vol. 46, 1914, pp. 192-201. 


sist for ten years, as in one of our examples, there is no 
logical reason why they cannot persist for a hundred or 
a thousand. The evidence of changes in climate during the 
historic period seems to suggest changes in precipitation 
much more than in temperature. Hence the strongest of 
all the arguments against historic changes of climate 
seems to be of relatively little weight, and the pulsatory 
hypothesis seems to be in accord with all the known facts. 
Before the true nature of climatic changes, whether 
historic or geologic, can be rightly understood, another 
point needs emphasis. When the pulsatory hypothesis 
was first framed, it fell into the same error as the hy- 
pothese, of nmfonnity and of progressive ehange-ehTt 
is, the assumption was made that the whole world is 
either growing drier or moister with each pulsation. A 
study of the ruins of Yucatan, in 1912, and of Guatemala, 
in 1913, as is explained in The Climatic Factor, has led to 
the conclusion that the climate of those regions has 
changed in the opposite way from the changes which 
appear to have taken place in the desert regions farther 
south. These Maya ruins in Central America are in many 
cases located in regions of such heavy rainfall, such dense 
forests, and such malignant fevers that habitation is now 
practically impossible. The land cannot be cultivated 
except in especially favorable places. The people are 
terribly weakened by disease and are among the lowest 
in Central America. Only a hundred miles from the un- 
healthful forests we find healthful areas, such as the 
coasts of Yucatan and the plateau of Guatemala. Here 
the vast majority of the population is gathered, the large 
towns are located, and the only progressive people are 
found. Nevertheless, in the past the region of the forests 
was the home of by far the most progressive people who 
are ever known to have lived in America previous to the 


days of Columbus. They alone brought to high perfection 
the art of sculpture ; they were the only American people 
who invented the art of writing. It seems scarcely credi- 
ble that such a people would have lived in the worst pos- 
sible habitat when far more favored regions were close 
at hand. Therefore it seems as if the climate of eastern 
Guatemala and Yucatan must have been relatively dry 
at some past time. The Maya chronology and traditions 
indicate that this was probably at the same time when 
moister conditions apparently prevailed in the subarid 
or desert portions of the United States and Asia. Fig. 3 
shows that today at times of many sunspots there is 
a similar opposition between a tendency toward stormi- 
ness and rain in subtropical regions and toward aridity 
in low latitudes near the heat equator. 

Thus our final conclusion is that during historic times 
there have been pulsatory changes of climate. These 
changes have been of the same type in regions having 
similar kinds of dimate, but of different and sometimes 
opposite types in places having diverse climates. As to 
the cause of the pulsations, they cannot have been due to 
the precession of the equinoxes nor apparently to any 
allied astronomical cause, for the time intervals are too 
short and too irregular. They cannot have been due to 
changes in the percentage of carbon dioxide in the atmos- 
phere, for not even the strongest believers in the climatic 
efficacy of that gas hold that its amount could fluctuate in 
any such violent way as would be necessary to explain 
the pulsations shown in the California curve of tree 
growth. Volcanic activity seems more probable as at least 
a partial cause, and it would be worth while to investigate 
the matter more fully. Nevertheless, it can apparently 
be only a minor cause. In the first place, the main effect 
of a cloud of dust is to alter the temperature, but 


Gregory 's summary of the palm and the vine shows that 
variations in temperature are apparently of very slight 
importance during historic times. Again, ruins on the 
bottoms of enclosed salt lakes, old beaches now under the 
water, and signs of irrigation ditches where none are now 
needed indicate a climate drier than the present. Vol- 
canic dust, however, cannot account for such a condi- 
tion, for at present the air seems to be practically free 
from such dust for long periods. Thus we now experience 
the greatest extreme which the volcanic hypothesis per- 
mits in one direction, but there have been greater ex- 
tremes in the same direction. The thermal solar hypothe- 
sis is likewise unable to explain the observed phenomena, 
for neither it nor the volcanic hypothesis offers any expla- 
nation of why the climate varies in one way in Medi- 
terranean climates and in an opposite way in regions 
near the heat equator. 

This leaves the cyclonic hypothesis. It seems to fit the 
facts, for variations in cyclonic storms cause some 
regions to be moister and others drier than usual. At the 
same time the variations in temperature are slight, and 
are apparently different in different regions, some places 
growing warm when others grow cool. In the next chap- 
ter we shall study this matter more fully, for it can best 
be appreciated by examining the course of events in a 
sp«Z century. 




IN order to give concreteness to our picture of the 
cUmatic pulsations of historic times let us take a 
specific period and see how its changes of climate 
were distributed over the globe and how they are related 
to the little changes which now take place in the sunspot 
cycle. We will take the fourteenth century of the Chris- 
tian era, especially the first half. This period is chosen 
because it is the last and hence the best known of the 
times when the climate of the earth seems to have taken 
a considerable swing toward the conditions which now 
prevail when the sun is most active, and which, if inten- 
sified, would apparently lead to glaciation. It has already 
been discussed in World Power and Evolution, but its 
importance and the fact that new evidence is constantly 
coming to light warrant a fuller discussion. 

To begin with Europe ; according to the careful account 
of Pettersson* the fourteenth century shows 

a record of extreme climatic variations. In the cold winters the 
rivers Rhine, Danube, Thames, and Po were frozen for weeks 
and months. On these cold winters there followed violent floods, 
so that the rivers mentioned inundated their valleys. Such floods 
are recorded in 55 summers in the 14th century. There is, of 

1 0. Pettersson : The connection between hydrographical and meteorologi- 
cal phenomena; Quarterly Journal of the Boyal Meteorological Society, VoL 
38, pp. 174-175. 


course, nothing astonishing in the fact that the inundations of 
the great rivers of Europe were more devastating 600 to 700 
years ago than in our days, when the flow of the rivers has been 
regulated by canals, locks, etc. ; but still the inundations in the 
13th and 14th centuries must have surpassed everything of that 
kind which has occurred since then. In 1342 the waters of the 
Rhine rose so high that they inundated the city of Mayence and 
the Cathedral ''usque ad cingulum hominis." The walls of 
Cologne were flooded so that they could be passed by boats in 
July. This occurred also in 1374 in the midst of the month of 
February, which is of course an unusual season for disasters of 
the kind. Again in other years the drought was so intense that 
the same rivers, the Danube, Rhine, and others, nearly dried up, 
and the Rhine could be forded at Cologne. This happened at least 
twice in the same century. There is one exceptional summer of 
such evil record that centuries afterwards it was spoken of as 
''the old hot summer of 1357." 

Pettersson goes on to speak of two oceanic phenomena 
on which the old chronicles lay greater stress than on 
all others : 

The first [is] the great storm-floods on the coast of the North 
Sea and the Baltic, which occurred so frequently that not less 
than nineteen floods of a destructiveness unparalleled in later 
times are recorded from the 14th century. The coastline of the 
North Sea was completely altered by these floods. Thus on 
January 16, 1300, half of the island Heligoland and many other 
islands were engulfed by the sea. The same fate overtook the 
island of Borkum, torn into several islands by the storm-flood of 
January 16, which remoulded the Frisian Islands into their 
present shape, when also Wendingstadt, on the island of Sylt, 
and Thiryu parishes were engulfed. This flood is known under 
the name of "the great man-drowning." The coasts of the Baltic 
also were exposed to storm-floods of unparalleled violence. On 
November 1, 1304, the island of Ruden was torn asunder from 
Rugen by the force of the waves. Time does not allow me to 
dwell upon individual disasters of this kind, but it will be well 


to note that of the nineteen great floods on record eighteen 
occurred in the cold season between the antunmal and yemal 

The second remarkable phenomenon mentioned by the chron- 
icles is the freezing of the entire Baltic, which occurred many 
times during the cold winters of these centuries. On such occsr 
sions it was possible to travel with carriages over the ice from 
Sweden to Bomholm and from Denmark to the Gterman coast 
(Lubeck), and in some cases even from Gotland to the coast of 

Norlind* says that **the only authentic accounts** of 
the complete freezing of the Baltic in the neighborhood 
of the Kattegat are in the years 1296, 1306, 1323, and 
1408. Of these 1296 is *'much the most uncertain,** while 
1323 was the coldest year ever recorded, as appears from 
the fact that horses and sleighs crossed regularly from 
Sweden to Gtermany on the ice. 

Not only central Europe and the shores of the North 
Sea were marked by climatic stress during the four- 
teenth century, but Scandinavia also suffered. As Petters- 
son puts it : 

On examining the historic (data) from the last centuries of 
the Middle Ages, Dr. Bull of Christiania has come to the con- 
clusion that the decay of the Norwegian kingdom was not so 
much a consequence of the political conditions at that time, as 
of the frequent failures of the harvest so that com [wheat] for 
bread had to be imported from Liibeck^ Rostock, Wismar and so 
forth. The Hansa Union undertook the importation and ob- 
tained political power by its economic influence. The Norwegian 
land-owners were forced to lower their rents. The population 
decreased and became impoverished. The revenue sank 60 to 70 
per cent. Even the income from Church property decreased. 

s A. Norlind : Einige Bemerkungen fiber das Klima der historischen Zeit 
nebst einem Yerzeichnis mittelaltlieher WittenmgB erBcheimmgen; Lands 
Univ. Araskrift, N. P., Vol. 10, 19U, 63 pp. 


In 1367 com was imported from Liibeck to a valne of one- 
half million kroner. The trade balance inclined to the disad- 
vantage of Norway whose sole article of export at that time was 
dried Ssh. (The production of fish increased enormously in the 
Baltic regions off south Sweden because of the same changes 
which were influencing the lands, but this did not benefit Nor- 
way.) Dr. BuU draws a comparison with the conditions described 
in the Sagas when Nordland [at the Arctic Circle] produced 
enough com to feed the inhabitants of the country. At the time 
of Asbjom Selsbane the chieftains in Trondhenas [still farther 
north in latitude 69^] grew so much com that they did not need 
to go southward to buy com unless three successive years of 
dearth had occurred. The province of Trondheim exported wheat 
to Iceland and so forth. Probably the turbulent political state 
of Scandinavia at the end of the Middle Ages was in a great 
measure due to unfavorable climatic conditions, which lowered 
the standard of life, and not entirely to misgovemment and 
political strife as has hitherto been taken for granted. 

During this same unfortunate first half of the four- 
teenth century England also suffered from conditions 
whichy if sufficiently intensified^ might be those of a gla- 
cial period. According to Thorwald Eogers* the severest 
famine ever experienced in England was that of 1315- 
1316^ and the next worst was in 1321. In f act, from 1308 
to 1322 great scarcity of food prevailed most of the time. 
Other famines of less severity occurred in 1351 and 1369. 
**The same cause was at work in all these cases/' says 
Bogers, '^incessant rain, and cold, stormy summers. It 
is said that the inclemency of the seasons affected the 
cattle, and that numbers perished from disease and 
want." After the bad harvest of 1315 the price of wheat, 
vrhich was already high, rose rapidly, and in May, 1316, 
was about five times the average. For a year or more 
thereafter it remained at three or four times the ordinary 

s Thorwald Bogers : A History of Agrieultnre and Prices in England. 


level. The severity of the famine may be jndged from the 
fact that previous to the Great War the most notable 
scarcity of wheat in modem England and the highest 
relative price was in December, 1800. At that time wheat 
cost neariy three times the usual amount, instead of five 
as in 1316. During the famine of the early fourteenth cen- 
tury * 4t is said that people were reduced to subsist upon 
roots, upon horses and dogs, and stories are told of even 
more terrible acts by reason of the extreme famine. '* The 
number of deaths was so great that the price of labor 
suffered a permanent rise of at least 10 per cent. There 
simply were not people enough left among the peasants 
to do the work demanded by the more prosperous class 
who had not suffered so much. 

After the famine came drought. The year 1325 appears 
to have been peculiarly dry, and 1331, 1344, 1362, 1374, 
and 1377 were also dry. In general these conditions do 
little harm in England. They are of interest chiefly as 
showing how excessive rain and drought are apt to 
succeed one another. 

These facts regarding northern and central Europe 
during the fourteenth century are particularly significant 
when compared with the conclusions which we have 
drawn in Earth and Sun from the growth of trees in 
Germany and from the distribution of storms. A careful 
study of all the facts shows that we are dealing with two 
distinct types of phenomena. In the first place, the climate 
of central Europe seems to have been peculiarly conti- 
nental during the fourteenth century. The winters were 
so cold that the rivers froze, and the summers were so 
wet that there were floods every other year or oftener. 
This seems to be merely an intensification of the condi- 
tions which prevail at the present time during periods of 
many sunspots, as indicated by the growth of trees at 


Eberswalde in Germany and by the number of storms in 
winter as compared with summer. The prevalence of 
droughts, especiaUy in the spring, is also not inconsistent 
with the existence of floods at other seasons, for one of 
the chief characteristics of a continental climate is that 
the variations from one season to another are more 
marked than in oceanic climates. Even the summer 
droughts are typically continental, for when continental 
conditions prevail, the difference between the same sea- 
son in different years is extreme, as is well illustrated in 
Kansas. It must always be remembered that what causes 
famine is not so much absolute dryness as a temporary 
diminution of the rainfall. 

The second type of phenomena is peculiarly oceanic in 
character. It consists of two parts, both of which are 
precisely what would be expected if a highly continental 
climate prevailed over the land. In the first place, at cer- 
tain times the cold area of high pressure, which is the 
predominating characteristic of a continent during the 
winter, apparently spread out over the neighboring 
oceans. Under such conditions an inland sea, such as the 
Baltic, would be frozen, so that horses could cross the ice 
even in the Far West. In the second place, because of the 
unusually high pressure over the continent, the baro- 
metric gradients apparently became intensified. Hence at 
the margin of the continental high-pressure area the 
winds were unusually strong and the storms of corre- 
sponding severity. Some of these storms may have 
passed entirely along oceanic tracks, while others in- 
vaded the borders of the land, and gave rise to the floods 
and to the wearing away of the coast described by 

Turning now to the east of Europe, Bruckner 's* study 

^E. Briiekner: Elimaficliwanlnuigen seit 1700, Vienna, 1891. 


of the Caspian Sea shows that that region as well as 
western Europe was subject to great climatic vicissitudes 
in the first half of the fourteenth century. In 1306-1307 
the Caspian Sea, after rising rapidly for several years, 
stood thirty-seven feet above the present level and it 
probably rose still higher during the succeeding decades. 
At least it remained at a high level, for Hamdulla, the 
Persian, tells us that in 1325 a place called Aboskun was 
under water.** 

Still further east the inland lake of Lop Nor also rose 
at about this time. According to a Chinese account the 
Dragon Town on the shore of Lop Nor was destroyed by 
a flood. From Himley's translation it appears that the 
level of the lake rose so as to overwhelm the city com- 
pletely. This would necessitate the expansion of the lake 
to a point eighty miles east of Lulan, and fully fifty from 
the present eastern end of the Kara Koshun marsh. The 
water would have to rise nearly, or quite, to a strand 
which is now clearly visible at a height of twelve feet 
above the modem lake or marsh. 

In India the fourteenth century was characterized by 
what appears to have been the most disastrous drought 
in all history. Apparently the decrease in rainfall here 
was as string as the Lrease in other parte of the 
world. No statistics are available but we are told that in 
the great famine which began in 1344 even the Mogul 
emperor was unable to obtain the necessaries of life for 
his household. No rain worth mentioning fell for years. 
In some places the famine lasted three or four years, and 
in some twelve, and entire cities were left without an in- 
habitant. In a later famine, 1769-1770, which occurred in 
Bengal shortly after the foundation of British rule in 

5 For a full discussion of the changes in the Caspian Sea see The Pulse 
of Asia, pp. 329-358. 


India, but while the native officials were still in power, 
a third of the population, or ten out of thirty millions, 
X>erished. The famine in the first half of the fourteenth 
century seems to have been far worse. These Indian 
famines were apparently due to weak summer monsoons 
caused presumably by the failure of central Asia to warm 
up as much as usual. The heavier snowfall, and the 
greater cloudiness of the siunmer there, which probably 
accompanied increased storminess, may have been the 

The New World as well as the Old appears to have 
been in a state of climatic stress during the first half of 
the fourteenth century. According to Pettersson, Green- 
land furnishes an example of this. At first the inhabitants 
of that northland were fairly prosperous and were able 
to approach from Iceland without much hindrance from 
the ice. Today the North Atlantic Ocean northeast of 
Iceland is full of drift ice much of the time. The border 
of the ice varies from season to season, but in general it 
extends westward from Iceland not far from the Arctic 
circle and then follows the coast of Greenland south- 
ward to Cape Farewell at the southern tip and around to 
the western side for fifty miles or more. Except under 
exceptional circumstances a ship cannot approach the 
coast until well northward on the comparatively ice-free 
west coast. In the old Sagas, however, nothing is said of 
ice in this region. The route from Iceland to Greenland 
is carefully described. In the earliest times it went from 
Iceland a trifle north of west so as to approach the coast 
of Greenland after as short an ocean passage as possible. 
Then it went down the coast in a region where approach 
is now practically impossible because of the ice. At that 
time this coast was icy close to the shore, but there is no 
sign that navigation was rendered difficult as is now the 


case. Today no navigator would think of keeping close 
inland. The old route also went north of the island on 
which Cape Farewell is located, although the narrow 
channel between the island and the mainland is now so 
blocked with ice that no modem vessel has ever pene- 
trated it. By the thirteenth century, however, there ap- 
pears to have been a change. In the Kungaspegel or 
Kings' Mirror, written at that time, navigators are 
warned not to make the east coast too soon on accoxmt 
of ice, but no new route is recommended in the neighbor- 
hood of Cape Farewell or elsewhere. Finally, however, 
at the end of the fourteenth century, nearly 150 years 
after the Kungaspegel, the old sailing route was aban- 
doned, and ships from Iceland sailed directly southwest 
to avoid the ice. As Pettersson says : 

... At the end of the thirteenth and the beginning of the 
fourteenth century the European civilization in Greenland was 
wiped out by an invasion of the aboriginal population. The col- 
onists in the Vesterbygd were driven from their homes and 
probably migrated to America leaving behind their cattle in the 
fields. So they were found by Ivar Bardsson, steward to the 
Bishop of Gardar, in his official journey thither in 1342. 

The Eskimo invasion must not be regarded as a common raid. 
It was the transmigration of a people, and like other big move- 
ments of this kind [was] impelled by altered conditions of 
nature, in this case the alterations of climate caused by [or 
which caused f] the advance of the ice. For their hunting and 
fishing the Eskimos require an at least partially open arctic 
sea. The seal, their principal prey, cannot live where the surface 
of the sea is entirely frozen over. The cause of the favorable 
conditions in the Viking-age was, according to my hypothesis, 
that the ice then melted at a higher latitude in the arctic seas. 

The Eskimos then lived further north in Greenland and 
North America. When the climate deteriorated and the sea which 
gave them their living was closed by ice the Eskimos had to find 


a more suitable neighborhood. This they found in the land 
colonized by the Norsemen whom they attacked and finally 

Finally, far to the south in Yucatan the ancient Maya 
civilization made its last flickering effort at about this 
time. Not much is known of this but in earlier periods 
the history of the Mayas seems to have agreed quite 
closely with the fluctuations in climate.* Among the 
Mayas, as we have seen, relatively dry periods were the 
times of greatest progress. 

Let us turn now to Fig. 3 once more and compare the 
climatic conditions of the fourteenth century with those 
of periods of increasing rainfall. Southern England, 
Ireland, and Scandinavia, where the crops were ruined 
by extensive rain and storms in summer, are places 
where storminess and rainfall now increase when sun- 
spots are numerous. Central Europe and the coasts of the 
North Sea, where flood and drought alternated, are re- 
gions which now have relatively less rain when sunspots 
increase than when they diminish. However, as appears 
from the trees measured by Douglass, the winters become 
more continental and hence cooler, thus corresponding to 
the cold winters of the fourteenth century when people 
walked on the ice from Scandinavia to Denmark. When 
such high pressure prevails in the winter, the total rain- 
fall is diminished, but nevertheless the storms are more 
severe than usual, especially in the spring. In south- 
eastern Europe, the part of the area whence the Caspian 
derives its water, appears to have less rainfall during 
times of increasing sunspots than when sunspots are few, 
but in an equally large area to the south, where the moun- 

• S. Q. Morley: The Inscriptions at Cop&n; Carnegie Inst, of Wash., No. 
219, 1920. 

Ellsworth Huntington: The Bed Man's Continent, 1919. 


tains are higher and the run-off of the rain is more rapid, 
the reverse is the case. This seems to mean that a slight 
diminution in the water poured in by the Volga would 
be more than compensated by the water derived from 
Persia and from the Oxus and Jaxartes rivers, which in 
the fourteenth century appear to have filled the Sea of 
Aral and overflowed in a large stream to the Caspian. 
Still farther east in central Asia, so far as the records go, 
most of the country receives more rain when sunspots 
are many than when they are few, which would agree 
with what happened when the Dragon Town was inun- 
dated. In India, on the contrary, there is a large area 
where the rainfall diminishes at times of many sunsi)ot8, 
thus agreeing with the terrible famine from which the 
Moguls suffered so severely. In the western hemisphere, 
Greenland, Arizona, and California are all parts of the 
area where the rain increases* with many sunspots, while 
Yucatan seems to lie in an area of the opposite type. Thus 
all the evidence seems to show that at times of climatic 
stress, such as the fourteenth century, the conditions 
are essentially the same as those which now prevail at 
times of increasing sunspots. 

As to the number of sunspots, there is little evidence 
previous to about 1750. Yet that Uttle is both interesting 
and important. Although sunspots have been observed 
with care in Europe only a little more than three cen- 
turies, the Chinese have records which go back nearly to 
the beginning of the Christian era. Of course the records 
are far from perfect, for the work was done by indi- 
viduals and not by any great organization which con- 
tinued the same methods from generation to generation. 
The mere fact that a good observer happened to use his 
smoked glass to advantage may cause a particular period 
to appear to have an unusual number of spots. On the 


other handy the fact that such an observer finds spots 
at some times and not at others tends to give a valuable 
check on his results, as does the comparison of one 
observer's work with that of another. Hence, in spite of 
many and obvious defects, most students of the problem 
agree that the Chinese record possesses much value, and 
that for a thousand years or more it gives a fairly true 
idea of the general aspect of the sun. In the Chinese 
records the years with many spots fall in groups, as 
would be expected, and are sometimes separated by long 
intervals. Certain centuries appear to have been marked 
by unusual spottedness. The most conspicuous of these 
is the fourteenth, when the years 1370 to 1385 were par- 
ticularly noteworthy, for spots large enough to be visible 
to the naked eye covered the sun much of the time. Hence 
Wolf ,^ who has made an exhaustive study of the matter, 
concludes that there was an absolute maximum of spots 
about 1372. While this date is avowedly open to question, 
the great abundance of sunspots at that time makes it 
probable that it cannot be far wrong. If this is so, it 
seems that the great climatic disturbances of which we 
have seen evidence in the fourteenth century occurred at 
a time when sunspots were increasing, or at least when 
solar activity was under some profoundly disturbing in- 
fluence. Thus the evidence seems to show not merely that 
the climate of historic times has been subject to im- 
portant pulsations, but that those pulsations were mag- 
nifications of the little climatic changes which now take 
place in sunspot cycles. The past and the present are 
apparently a unit except as to the intensity of the 

7 Bee BnmniaTy of Wolf's work with additional information bj H. Fritz; 
Zurich Vierteljahrschrift, Vol. 38, 1893, pp. 77-107. 



THE remarkable phenomena of glacial periods 
afford perhaps the best available test to which 
any climatic hypothesis can be subjected. In this 
chapter and the two that follow, we shall apply this test. 
Since much more is known about the recent Great Ice 
Age, or Pleistocene glaciation, than about the more 
ancient glaciations, the problems of the Pleistocene wUl 
receive especial attention. In the present chapter the 
oncoming of glaciation and the subsequent disappear- 
ance of the ice will be outlined in the light of what would 
be expected according to the solar-cyclonic hypothesis. 
Then in the next chapter several problems of especial 
climatic significance will be considered, such as the locali- 
zation of ice sheets, the succession of severe glacial and 
mild inter-glacial epochs, the sudden commencement of 
glaciation and the peculiar variations in the height of the 
snow line. Other topics to be considered are the occur- 
rence of pluvial or rainy climates in non-glaciated re- 
gions, and glaciation near sea level in subtropical 
latitudes during the Permian and Proterozoic. Then in 
Chapter IX we shall consider the development and dis- 
tribution of the remarkable deposits of wind-blown ma- 
terial known as loess. 
Facts not considered at the time of framing an hypothe- 

1 This chapter is an amplification and revision of the sketch of the glacial 
period contained in The Solar Hypothesis of Climatic Changes; Boll. GeoL 
Soc. Am., Vol. 25, 1914. 


sis are especially significant in testing it. In this particu- 
lar case, the cyclonic hypothesis was framed to explain 
the historic changes of climate revealed by a study of 
ruins, tree rings, and the terraces of streams and lakes, 
without special thought of glaciation or other geologic 
changes. Indeed, the hypothesis had reached nearly its 
present form before much attention was given to geo- 
logical phases of the problem. Nevertheless, it appears 
to meet even this severe test. 

According to the solar-cyclonic hypothesis, the Pleisto- 
cene glacial period was inaugurated at a time when cer- 
tain terrestrial conditions tended to make the earth 
especially favorable for glaciation. How these conditions 
arose will be considered later. Here it is enough to state 
what they were. Chief among them was the fact that the 
continents stood unusually high and were unusually 
large. This, however, was not the primary cause of gla- 
ciation, for many of the areas which were soon to be 
glaciated were little above sea level. For example, it 
seems clear that New England stood less than a thousand 
feet higher tiian now. Indeed, Salisbury^ estimates that 
eastern North America in general stood not more than 
a few hundred feet higher than now, and W. B. Wright* 
reaches the same conclusion in respect to the British 
Isles. Nevertheless, widespread lands, even if they are 
not all high, lead to climatic conditions which favor 
glaciation. For example, enlarged continents cause low 
temperature in high latitudes because they interfere with 
the ocean currents that carry heat polewards. Such con- 
tinents also cause relatively cold winters, for lands cool 
much sooner than does the ocean. Another result is a 

>B. D. Salisbury: Physical Geography of the PleistoeenOi in Outlines of 
Geologic History, by Willis, Salisbury, and others, 1910, p. 265. 
s The Quaternary Ice Age, 1914, p. 364. 


diminntion of water vapor, not only because cold air 
cannot hold much vapor, but also because the oceanic 
area from which evaporation takes place is reduced by 
the emergence of the continents. Again, when the conti- 
nents are extensive the amount of carbonic add gas in 
the atmosphere probably decreases, for the augmented 
erosion due to uplift exposes much igneous rock to the 
air, and weathering consiunes the atmospheric carbon 
dioxide. When the supply of water vapor and of atmos- 
pheric carbon dioxide is smaU, an extreme type of climate 
usually prevails. The combined result of all these condi- 
tions is that continental emergence causes the climate to 
be somewhat cool and to be marked by relatively great 
contrasts from season to season and from latitude to 

When the terrestrial conditions thus permitted glada- 
I - * ^ V tion, unusual solar activity is supposed to have greatly 

increased the number and severity of storms and to have 
altered their location, just as now happens at times of 
many sunspots. If such a change in storminess had oc- 
curred when terrestrial conditions were unfavorable for 
glaciation, as, for example, when the lands were low and 
there were widespread epicontinental seas in middle and 
high latitudes, glaciation might not have resulted. In the 
Pleistocene, however, terrestrial conditions permitted 
glaciation, and therefore the supposed increase in stormi- 
ness caused great ice sheets. 

The conditions which prevail at times of increased 
storminess have been discussed in detail in Earth and 
Sun. Those which apparently brought on glaciation seem 
to have acted as follows : In the first place the storminess 
lowered the temperature of the earth *s surface in several 
ways. The most important of these was the rapid upward 
convection in the centers of cyclonic storms whereby 


abundant heat was carried to high levels where most of it 
was radiated away into space. The marked increase in 
the number of tropical cyclones which accompanies in- 
creased solar activity was probably important in this 
respect. Such cyclones carry vast quantities of heat and 
moisture out of the tropics. The moisture, to be sure, 
liberates heat upon condensing, but as condensation 
occurs above the earth's surface, much of the heat 
escapes into space. Another reason for low temperature 
was that under the influence of the supposedly numerous 
storms of Pleistocene times evaporation over the oceans 
must have increased. This is largely because the velocity 
of the winds is relatively great when storms are strong 
and such winds are powerful agents of evaporation. But 
evaporation requires heat, and hence the strong winds 
lower the temperature.** 

The second great condition which enabled increased 
storminess to bring on glaciation was the location of the 
storm tracks. Kullmer's maps, as illustrated in Fig. 2, 
suggest that a great increase in solar activity, such as is 
postulated in the Pleistocene, might shift the main storm 
track poleward even more than it is shifted by the milder 
solar changes during the twelve-year sunspot cycle. If 
this is so, the main track would tend to cross North 
America through the middle of Canada instead of near 
the southern border. Thus there would be an increase in 
precipitation in about the latitude of the Keewatin and 
Labradorean centers of glaciation. From what is known 
of storm tracks in Europe, the main increase in the in- 
tensity of storms would probably center in Scandinavia. 
Fig. 3 in Chapter V bears this out. That figure, it will be 
recalled, shows what happens to precipitation when solar 

»»Por fuller disciiBsion of climatic controls see 8. 8. Visher: Seventy 
Laws of Climate, Annals Assoc. Am. Geographers, 1922. 



activity is increasing. A high rate of precipitation is 
especially marked in the boreal storm track, that is, in 
the northern United States, southern Canada, and north- 
western Europe. 

Another important condition in bringing on glaciation 
would be the fact that when storms are numerous the 
total precipitation appears to increase in spite of the 
slightiy lower temperature. This is largely because of the 
greater evaporation. The excessive evaporation arises 
partly from the rapidity of the winds, as already stated, 
and partiy from the fact that in areas where the air is 
clear the sun would presumably be able to act more effec- 
tively than now. It would do so because at times of abun- 
dant sunspots the sun in our own day has a higher solar 
constant than at times of milder activity. Our whole 
hypothesis is based on the supposition that what now 
happens at times of many sunspots was intensified in 
glacial periods. 

A fourth condition which would cause glaciation to 
result from great solar activity would be the fact that 
the portion of the yearly precipitation falling as snow 
would increase, while the proportion of rain would dimin- 
ish in the main storm track. This would arise partiy be- 
cause the storms would be located farther north than 
now, and partly because of the diminution in temperature 
due to the increased convection. The snow in itself would 
still further lower the temperature, for snow is an excel- 
lent reflector of sunlight. The increased cloudiness which 
would accompany the more abundant storms would also 
cause an unusually great reflection of the sunlight and 
still further lower the temperature. Thus at times of 
many sunspots a strong tendency toward the accumula- 
tion of snow would arise from the rapid convection and 
consequent low temperature, from the northern location 


of storms, from the increased evaporation and precipita- 
tion, from the larger percentage of snowy rather than 
rainy precipitation, and from the great loss of heat due 
to reflection from clouds and snow. 

If events at the beginning of the last glacial period 
took place in accordance with the cyclonic hypothesis, as 
outlined above, one of the inevitable results would be the 
production of snowfields. The places where snow would 
accumulate in special quantities would be central Canada, 
the Labrador plateau, and Scandinavia, as well as cer- 
tain mountain regions. As soon as a snowfield became 
somewhat extensive, it would begin to produce striking 
climatic alterations in addition to those to which it owed 
its origin.* For example, within a snowfield the summers 
remain relatively cold. Hence such a field is likely to be 
an area of high pressure at all seasons. The fact that the 
snowfield is always a place of relatively high pressure 
results in outblowing surface winds except when these 
are temporarily overcome by the passage of strong cy- 
clonic storms. The storms, however, tend to be concen- 
trated near the margins of the ice throughout the year 
instead of following different paths in each of the four 
seasons. This is partly because cyclonic lows always 
avoid places of high pressure and are thus pushed out 
of the areas where permanent snow has accumulated. 
On the other hand, at times of many sunspots, as KuU- 
mer has shown, the main storm track tends to be drawn 

'A Many of these alterations are implied or diBCussed in the following 

1. F. W. Harmer: Influence of Winds upon the Climate of the Pleisto- 
cene; Qaart. Jour. QeoL Soe., Vol. 57, 1901, p. 405. 

2. 0. E. P. Brooks: Meteorologicid Conditions of an Ice Sheet; Quart. 
Jour. Boyal Meteorol. Soc, Vol. 40, 1914, pp. 53-70, and The Evolution of 
Climate in Northwest Europe; op. cit,, Vol. 47, 1921, pp. 173-194. 

3. W. H. Hobbs: The B61e of the Glacial Anticyclone in the Air Circu- 
lation of the Globe; Proc. Am. Phil. Soc, Vol. 54, 1915, pp. 185-225. 



poleward, perhaps by electrical conditions. Hence when 
a snowfield is present in the north, the lows, instead of 
migrating mnch farther north in summer than in winter, 
as they now do, would merely crowd on to the snowfield 
a little farther in summer than in winter. Thus the heavy 
precipitation which is usual in humid climates near the 
centers of lows would take place near the advancing 
margin of the snowfield and cause the field to expand 
still farther southward. 

The tendency toward the accumulation of snow on the 
margins of the snowfields would be intensified not only 
by the actual storms themselves, but by other conditions. 
For example, the coldness of the snow would tend to 
cause prompt condensation of the moisture brought by 
the winds that blow toward the storm centers from low 
latitudes. Again, in spite of the general dryness of the 
air over a snowfield, the lower air contains some moisture 
due to evaporation from the snow by day during the 
clear sunny weather of anti-cyclones or highs. Where this 
is sufficient, the cold surface of the snowfields tends to 
produce a frozen fog whenever the snowfield is cooled 
by radiation, as happens at night and during the passage 
of highs. Such a frozen fog is an effective reflector of 
solar radiation. Moreover, because ice has only half the 
specific heat of water, and is much more transparent to 
heat, such a ** radiation fog** composed of ice crystals is 
a much less effective retainer of heat than clouds or fog 
made of unfrozen water particles. Shallow fogs of this 
type are described by several polar expeditions. They 
clearly retard the melting of the snow and thus help the 
icefield to grow. 

For all these reasons, so long as storminess remained 
great, the Pleistocene snowfields, according to the solar 
hypothesis, must have deepened and expanded. In due 


time some of the snow was converted into glacial ice. 
When that occurred, the growth of the snowfield as well 
as of the ice cap must have been accelerated by glacial 
movement. Under snch circumstances, as the ice crowded 
southward toward the source of the moisture by which it 
grew, the area of high pressure produced by its low 
temperature would expand. This would force the storm 
track southward in spite of the contrary tendency due to 
the sun. When the ice sheet had become very extensive, 
the track would be crowded relatively near to the north- 
em margin of the trade-wind belt. Indeed, the Pleisto- 
cene ice sheets, at the time of their maximum extension, 
reached almost as far south as the latitude now marking 
the northern limit of the trade-wind belt in summer. 
As the storm track with its frequent low pressure and the 
subtropical belt with its high pressure were forced nearer 
and nearer together, the barometric gradient between 
the two presumably became greater, winds became 
stronger, and the storms more intense. 

This zonal crowding would be of special importance in 
summer, at which time it would also be most pronounced. 
Li the first place, the storms would be crowded far upon 
the ice cap which would then be protected from the sun 
by a cover of fog and cloud more fully than at any other 
season. Furthermore, the close approach of the trade- 
wind belt to the storm belt would result in a great in- 
crease in the amount of moisture drawn from the belt of 
evaporation which the trade winds dominate. In the 
trade-wind belt, clear skies and liigh temperature make 
evaporation especially rapid. Indeed, in spite of the vast 
deserts it is probable that more than three-fourths of the 
total evaporation now taking place on the earth occurs 
in the belt of trades, an area which includes about one- 
half of the earth's surface. 


The agency which could produce this increased draw- 
ing northward of moisture from the trade-wind belt 
would be the winds blowing into the lows. According to 
the cyclonic hypothesis, many of these lows would be so 
strong that they would temporarily break down the sub- 
tropical belt of high pressure which now usually prevails 
between the trades and the zone of westerly winds. This 
belt is even now often broken by tropical cyclones. If the 
storms of more northerly regions temporarily destroyed 
the subtropical high-pressure belt, even though they still 
remained on its northern side, they would divert part of 
the trade winds. Hence the air which now is carried 
obliquely equatorward by those winds would be carried 
spirally northward into the cyclonic lows. Precipitation 
in the storm track on the margin of the relatively cold ice 
sheet would thus be much increased, for most winds from 
low latitudes carry abundant moisture. Such a diversion 
of moisture from low latitudes probably explains the 
deficiency of precipitation along the heat equator at 
times of solar activity, as shown in Fig. 3. Taken as a 
whole, the summer conditions, according to the cyclonic 
hypothesis, would be such that increased evaporation in 
low latitudes would cooperate with increased storminess, 
cloudiness, and fog in higher latitudes to preserve and 
increase the accumulation of ice upon the borders of the 
ice sheet The greater the storminess, the more this would 
be true and the more the ice sheet would be able to hold 
its own against melting in summer. Such a combination 
of precipitation and of protection from the sun is espe- 
cially important if an ice sheet is to grow. 

The meteorologist needs no geologic evidence that the 
storm track was shoved equatorward by the growth of 
the ice sheet, for he observes a similar shifting whenever 
a winter ^s snow cap occupies part of the normal storm 


tract The geologist, however, may welcome geologic 
evidence that such an extreme shift of the storm track 
actually occurred during the Pleistocene. Harmer, in 
1901, first pointed out the evidence which was repeated 
with approval by Wright of the Ireland Geological Sur- 
vey in 1914/ According to these authorities, numerous 
boulders of a distinctive chalk were deposited by Pleisto- 
cene icebergs along the coast of Ireland. Their distribu- 
tion shows that at the time of maximum glaciation the 
strong winds along the south coast of Ireland were from 
the northeast while today they are from the southwest. 
Such a reversal could apparently be produced only by a 
southward shift of the center of the main storm track 
from its present position in northern Ireland, Scotland, 
and Norway to a position across northern France, central 
Germany, and middle Russia. This would mean that while 
now the centers of the lows conamonly move northeast- 
ward a short distance north of southern Ireland, they 
formerly moved eastward a short distance south of Ire- 
land. It will be recalled that in the northern hemisphere 
the winds spiral into a low counter-clockwise and that 
they are strongest near the center. When the centers pass 
not far north of a given point, the strong winds therefore 
blow from the west or southwest, while when the centers 
pass just south of that point, the strong winds come from 
the east or northeast. 

In addition to the consequences of the crowding of the 
storm track toward the trade-wind belt, several other 
conditions presumably operated to favor the growth of 
the ice sheet. For example, the lowering of the sea level 
by the removal of water to form the snowfields and 
glaciers interfered with warm currents. It also increased 
the rate of erosion, for it was equivalent to an uplift of 

B W. B. Wright: The Quaternary lee Age, 1914, p. 100. 


all the land. One consequence of erosion and weathering 
was presumably a diminution of the carbon dioxide in 
.the atmosphere, for although the ice covered perhaps a 
tenth of the lands and interfered with carbonation to that 
extent, the removal of large quantities of soil by acceler- 
ated erosion on the other nine-tenths perhaps more than 
counterbalanced the protective effect of the ice. At the 
same time, the general lowering of the temperature of the 
ocean as well as the lands increased the ocean's capacity 
for carbon dioxide and thus facilitated absorption. At a 
temperature of 50°F. water absorbs 32 per cent more 
carbon dioxide than at 68°. The high waves produced by 
the severe storms must have had a similar effect on a 
small scale. Thus the percentage of carbon dioxide in the 
atmosphere was presumably diminished. Of less signifi- 
cance than these changes in the lands and the air, but 
perhaps not negligible, was the increased salinity of the 
ocean which accompanied the removal of water to form 
snow, and the increase of the dissolved mineral load of 
the rejuvenated streams. Increased salinity slows up the 
deep-sea circulation, as we shall see in a later chapter. 
This increases the contrasts from zone to zone. 

At times of great solar activity the agencies mentioned 
above would apparently cooperate to cause an advance of 
ice sheets into lower latitudes. The degree of solar activ- 
ity would have much to do with the final extent of the ice 
sheets. Nevertheless, certain terrestrial conditions would 
tend to set limits beyond which the ice would not greatly 
advance unless the storminess were extraordinarily 
severe. The most obvious of these conditions is the loca- 
tion of oceans and of deserts or semi-arid regions. The 
southwestward advance of the European ice sheet and 
the southeastward advance of the Labradorean sheet in 
America were stopped by the Atlantic. The semi-aridity 


of the Great Plains, produced by their position in the lee 
of the Bocky Mountains, stopped the advance of the 
Keewatin ice sheet toward the southwest. The advance of 
the European ice sheet southeast seems to have been 
stopped for similar reasons. The cessation of the advance 
would be brought about in such an area not alone by the 
light precipitation and abundant sunshine, but by the 
dryness of the air, and also by the power of dust to ab- 
sorb the sun's heat. Much dust would presumably be 
drawn in from the dry regions by passing cyclonic storms 
and would be scattered over the ice. 

The advance of the ice is also slowed up by a rugged 
topography, as among the Appalachians in northern 
Pennsylvania. Such a toi)ography besides opposing a 
physical obstruction to the movement of the ice provides 
bare south-facing slopes which the sun warms effectively. 
Such warm slopes are unfavorable to glacial advance. 
The rugged topography was perhaps quite as effective as 
the altitude of the Appalachians in causing the conspicu- 
ous northward dent in the glacial margin in Pennsyl- 
vania. Where glaciers lie in mountain valleys the advance 
beyond a certain point is often interfered with by the 
deployment of the ice at the mouths of gorges. Evapora- 
tion and melting are more rapid where a glacier is broad 
and thin than where it is narrow and thick, as in a gorge. 
Again, where the topography or the location of oceans or 
dry areas causes the glacial lobes to be long and narrow, 
the elongation of the lobe is apparently checked in sev- 
eral ways. Toward the end of the lobe, melting and 
evaporation increase rapidly because the planetary 
westerly winds are more likely to overcome the glacial 
winds and sweep across a long, narrow lobe than across 
a broad one. As they cross the lobe, they accelerate 
evaporation, and probably lessen cloudiness, with a con- 


sequent augmentation of melting. Moreover, although 
lows rarely cross a broad ice sheet, they do cross a 
narrow lobe. For example, Nansen records that strong 
lows occasionally cross the narrow southern part of the 
Greenland ice sheet. The longer the lobe, the more likely 
it is that lows will cross it, instead of following its mar- 
gin. Lows which cross a lobe do not yield so much snow 
to the tip as do those which follow the margin. Hence 
elongation is retarded and finally stopped even without 
a change in the earth 's general climate. 

Because of these various reasons the advances of the 
ice during the several epochs of a glacial period might 
be approximately equal, even if the durations of the 
periods of storminess and low temperature were differ- 
ent. Indeed, they might be sub-equal, even if the periods 
differed in intensity as well as length. Differences in the 
periods would apparently be manifested less in the ex- 
tent of the ice than in the depth of glacial erosion and in 
the thickness of the terminal moraines, outwash plains, 
and other glacial or glacio-fluvial formations. 

Having completed the consideration of the conditions 
leading to the advance of the ice, let us now consider the 
condition of North America at the time of maximum 
glaciation.^ Over an area of nearly four million square 
miles, occupying practically all the northern half of the 
continent and part of the southern half, as appears in 
Fig. 6, the surface was a monotonous and almost level 
plain of ice covered with snow. When viewed from a 
high altitude, all parts except the margins must have 
presented a uniformly white and sparkling appearance. 
Along the margins, however, except to the north, the 

« The description of the distribution of the iee sheet is based on T. G. 
Chamberlin 's wall map of North America at the wn^imp Tn of glaciation, 


whiteness was irregular, for the view must have included 
not only fresh snow, but moving clouds and dirty snow 
or ice. Along the borders where melting was in progress 
there was presumably more or less spottedness due to 
morainal material or glacial debris brought to the sur- 
face by ice shearage and wastage. Along the dry south- 
western border it is also possible that there were numer- 
ous dark spots due to dust blown onto the ice by the 

The great white sheet with its ragged border was 
roughly circular in form, with its center in central 
Canada. Yet there were many departures from a per- 
fectly circular form. Some were due to the oceans, for, 
except in northern Alaska, the ice extended into the 
ocean all the way from New Jersey around by the north 
to Washington. On the south, topographic conditions 
made the margin depart from a simple arc From New 
Jersey to Ohio it swung northward. In the Mississippi 
Valley it reached far south; indeed most of the broad 
wedge between the Ohio and the Missouri rivers was 
occupied by ice. From latitude 37° near the junction of 
the Missouri and the Mississippi, however, the ice margin 
extended almost due north along the Missouri to central 
North Dakota. It then stretched westward to the Rockies. 
Farther west lowland glaciation was abundant as far 
south as western Washington. In the Bockies, the Cas- 
cades, and the Sierra Nevadas glaciation was common as 
far south as Colorado and southern California, respec- 
tively, and snowfields were doubtless extensive enough to 
make these ranges ribbons of white. Between these lofty 
ranges lay a great unglaciated region, but even in the 
Great Basin itself, in spite of its present aridity, certain 
ranges carried glaciers, while great lakes expanded 


In this vast field of snow the glacial ice slowly crept 
outward, possibly at an average speed of half a foot a 
day, but varying from almost nothing in winter at the 
north, to several feet a day in summer at the south/ The 
force which caused the movement was the presence of 
the ice piled up not far from the margins. Almost cer- 
tainly, however, there was no great dome from the 
center in Canada outward, as some early writers as- 
sumed. Such a dome would require that the ice be many 
thousands of feet thick near its center. This is impos- 
sible because of the fact that ice is more voluminous than 
water (about 9 per cent near the freezing point). Hence 
when subjected to sufficient pressure it changes to the 
liquid form. As friction and internal heat tend to keep 
the bottom of a glacier warm, even in cold regions, the 
probabilities are that only under very special conditions 
was a continental ice sheet much thicker than about 2500 
feet. In Antarctica, where the temperature is much lower 
than was probably attained in the United States, the ice 
sheet is nearly level, several expeditions having traveled 
hundreds of miles with practically no change in altitude. 
In Shackleton's trip almost to the South Pole, he en- 
countered a general rise of 3000 feet in 1200 miles. Moun- 
tains, however, projected through the ice even near the 
pole and the geologists conclude that the ice is not very 
thick even at the world 's coldest point, the South Pole. 

Along the margin of the ice there were two sorts of 
movement, much more rapid than the slow creep of the 
ice. One was produced by the outward drift of snow 
carried by the outblowing dry winds and the other and 
more important was due to the passage of cyclonic 
storms. Along the border of the ice sheet, except at the 

7 Chamberlin and Salisbury: Geology, 1906, Vol. 3, and W. H. Hobbs: 
Characteristics of Existing Glaciers, 1911. 


north, storm presumably closely followed storm. Their 
movement, we judge, was relatively slow until near the 
southern end of the Mississippi lobe, but when this point 
was passed they moved much more rapidly, for then they 
could go toward instead of away from the far northern 
path which the sun prescribes when solar activity is 
great. The storms brought much snow to the icefield, 
perhaps sometimes in favored places as much as the hun- 
dred feet a year which is recorded for some winters in the 
Sierras at present. Even the unglaciated intermontane 
Great Basin presumably received considerable precipi- 
tation, perhaps twice as much as its present scanty 
supply. The rainfall was enough to support many lakes, 
one of which was ten times as large as Great Salt Lake ; 
and grass was doubtless abimdant upon many slopes 
which are now dry and barren. The relatively heavy 
precipitation in the Great Basin was probably due pri- 
marily to the increased number of storms, but may also 
have been much influenced by their slow eastward move- 
ment. The lows presumably moved slowly in that general 
region not only because they were retarded and turned 
from their normal path by the cold ice to the east, but 
because during the summer the area between the Sierra 
snowfields on the west and the Rocky Moimtain and Mis- 
sissippi Valley snowfields on the east was relatively 
warm. Hence it was normally a place of low pressure 
and therefore of inblowing winds. Slow-moving lows are 
much more effective than fast-moving ones in drawing 
moisture northwestward from the Gulf of Mexico, for 
they give the moisture more time to move spirally first 
northeast, under the influence of the normal south- 
westerly winds, then northwest and finally southwest as 
it approaches the storm center. In the case of the present 
lows, before much moisture-laden air can describe such 


a circuit, first eastward and then westward, the storm 
center has nearly always moved eastward across the 
BocMes and even across the Great Plains. A result of this 
is the regular decrease in precipitation northward, north- 
westward, and westward from the Gulf of Mexico. 

Along the part of the glacial margins where for more 
than 3000 miles the North American ice entered the 
Atlantic and the Pacific oceans, myriads of great blocks 
broke off and floated away as stately icebergs, to scatter 
boulders far over the ocean floor and to melt in warmer 
climes. Where the margin lay upon the lands numerous 
streams issued from beneath the ice, milk-white with 
rock flour, and built up great outwash plains and valley 
trains of gravel and sand. Here and there, just beyond 
the ice, marginal lakes of strange shapes occupied valleys 
which had been dammed by the advancing ice. In many 
of them the water level rose until it reached some low 
point in the divide and then overflowed, forming rapids 
and waterfalls. Indeed, many of the waterfalls of the 
eastern United States and Canada were formed in just 
this way and not a few streams now occupy courses 
through ridges instead of parallel to them, as in pre- 
glacial times. 

In the zone to the south of the continental ice sheet, 
the plant and animal life of boreal, cool temperate, and 
warm temperate regions commingled curiously. Heather 
and Arctic willow crowded out elm and oak; musk ox, 
hairy mammoth, and marmot contested with deer, chip- 
munk, and skunk for a chance to live. Near the ice on 
slopes exposed to the cold glacial gales, the immigrant 
boreal species were dominant, but not far away in more 
protected areas the species that had formerly lived there 
held their own. In Europe during the last two advances 
of the great ice sheet the caveman also struggled with 


fierce animals and a fiercer climate to maintain life in an 
area whose habitabiUty had long been decreasing. 

The next step in our history of gladation is to outline 
the disappearance of the ice sheets. When a decrease in 
solar activity produced a corresponding decrease in 
storminesSy several influences presumably combined to 
cause the disappearance of the ice. Most of their results 
are the reverse of those which brought on glaciation. A 
few special aspects, however, some of which have been 
discussed in Earth and Sun, ought to be brought to mind. 
A diminution in storminess lessens upward convection, 
wind velocity, and evaporation, and these changes, if they 
occurred, must have united to raise the temperature of 
the lower air by reducing the escape of heat. Again a 
decrease in the number and intensity of tropical cyclones 
presumably lessened the amount of moisture carried into 
mid-latitudes, and thus diminished the precipitation. The 
diminution of snowfall on the ice sheets when storminess 
diimnished was probably highly important. The amount 
of precipitation on the sheets was presumably lessened 
still further by changes in the storminess of middle 
latitudes. When storminess diminishes, the lows follow a 
less definite path, as Kullmer's maps show, and on the 
average a more southerly path. Thus, instead of all the 
lows contributing snow to the ice sheet, a large fraction 
of the relatively few remaining lows would bring rain to 
areas south of the ice sheet. As storminess decreased, the 
trades and westerlies probably became steadier, and thus 
carried to high latitudes more warm water than when 
often interrupted by storms. Steadier southwesterly 
winds must have produced a greater movement of atmos- 
pheric as well as oceanic heat to high latitudes. The 
warming due to these two causes was probably the chief 
reason for the disappearance of the European ice sheet 


and of those on the Pacific coast of North America. The 
two greater American ice sheets, however, and the 
glaciers elsewhere in the lee of high mountain ranges, 
probably disappeared chiefly because of lessened pre- 
cipitation. If there were no cyclonic storms to draw mois- 
ture northward from the Gulf of Mexico, most of North 
America east of the Eocky Mountain barrier would be 
arid. Therefore a diminution of storminess would be 
particularly effective in causing the disappearance of ice 
sheets in these regions. 

That evaporation was an especially important factor 
in causing the ice from the Keewatin center to disappear, 
is suggested by the relatively small amount of water- 
sorted material in its drift. In South Dakota, for ex- 
ample, less than 10 per cent of the drift is stratified.* On 
the other hand, Salisbury estimates that perhaps a third 
of the Labradorean drift in eastern Wisconsin is crudely 
stratified, about half of that in New Jersey, and more 
than half of the drift in western Europe. 

When the sun's activity began to diminish, all these 
conditions, as well as several others, would cooperate to 
cause the ice sheets to disappear. Step by step with their 
disappearance, the amelioration of the climate would 
progress so long as the period of solar inactivity con- 
tinued and storms were rare. If the inactivity continued 
long enough, it would result in a fairly mild climate in 
high latitudes, though so long as the continents were 
emergent this mildness would not be of the extreme type. 
The inauguration of another cycle of increased disturb- 
ance of the Sim, with a marked increase in storminess, 
would inaugurate another glacial epoch. Thus a succes- 
sion of glacial and inter-glacial epochs might continue so 
long as the sun was repeatedly disturbed. 

8S. 8. Visher: The Geography of South Dakota; S. D. Geol. Sury., 1918. 


HAYING outlined in general terms the ooming of 
the ice sheets and their disappearance, we are 
now ready to discuss certain problems of com- 
pelling climatic interest. The discussion will be grouped 
under five heads: (I) the localization of glaciation; (II) 
the sudden coming of glaciation; (III) peculiar varia- 
tions in the height of the snow line and of glaciation; 
(IV) lakes and other evidences of humidity in ungla- 
ciated regions during the glacial epochs ; (V ) glaciation 
at sea level and in low latitudes in the Permian and 
Proterozoic eras. The discussion of perhaps the most 
difficult of all climatic problems of glaciation, that of the 
succession of cold glacial and mild inter-glacial epochs, 
has been postponed to the next to the final chapter of this 
book. It cannot be properly considered until we take up 
the history of solar disturbances. 

I. The first problem, the localization of the ice sheets, 
arises from the fact that in both the Pleistocene and the 
Permian periods glaciation was remarkably limited. In 
neither period were all parts of high latitudes glaciated ; 
yet in both cases glaciation occurred in large regions in 
lower latitudes. Many explanations of this localization 
have been offered, but most are entirely inadequate. Even 
hypotheses with something of proven worth, such as 
those of variations in volcanic dust and in atmospheric 


carbon dioxide, fail to account for localization. The 
cyclonic form of the solar hypothesis, however, seems to 
afford a satisfactory explanation. 

The distribution of the ice in the last glacial period is 
well known, and is shown in Fig. 6. Four-fifths of the 
ice-covered area, which was eight million square miles, 
more or less, was near the borders of the North Atlantic 
in eastern North America and northwestern Europe. 
The ice spread out from two great centers in North 
America, the Labradorean east of Hudson Bay, and the 
Keewatin west of the bay. There were also many glaciers 
in the western mountains, especially in Canada, while 
subordinate centers occurred in Newfoundland, the Adi- 
Tondacks, and the White Mountains. The main ice sheet 
at its maximum extension reached as far south as lati- 
tude 39^ in Kansas and Kentucky, and 37^ in Illinois. 
Huge boulders were transferred more than one thousand 
miles from their source in Canada. The northward ex- 
tension was somewhat less. Indeed, the northern margin 
of the continent was apparently relatively little glaciated 
and much of Alaska unglaciated. Why should northern 
Kentucky be glaciated when northern Aiaska was not f 

In Europe the chief center from which the continental 
glacier moved was the Scandinavian highlands. It pushed 
across the depression now occupied by the Baltic to 
southern Russia and across the North Sea depression 
to England and Belgium. The Alps formed a center of 
considerable importance, and there were minor centers 
in Scotland, Ireland, the Pyrenees, Apennines, Caucasus, 
and Urals. In Asia numerous ranges also contained large 
glaciers, but practically all the glaciation was of the 
alpine type and very little of the vast northern lowland 
was covered with ice. 

In the southern hemisphere glaciation at low latitudes 


was less striking than in the northern hemisphere. Most 
of the increase in the areas of ice was confined to moun- 
tains which today receive heavy precipitation and still 
contain small glaciers. Indeed, except for relatively slight 
gladation in the Australian Alps and in Tasmania, most 
of the Pleistocene glaciation in the southern hemisphere 
was merely an extension of existing glaciers, such as 
those of south Chile, New Zealand, and the Andes. Never- 
theless, fairly extensive glaciation existed much nearer 
the equator than is now the case. 

In considering the localization of Pleistocene glacia- 
tion, three main factors must be taken into account, 
namely, temperature, topography, and precipitation. The 
absence of glaciation in large parts of the Arctic regions 
of North America and of Asia makes it certain that low 
temperature was not the controlling factor. Aiside from 
Antarctica, the coldest place in the world is northeastern 
Siberia. There for seven months the average temperature 
is below 0°C., while the mean for the whole year is 
below — 10° C. If the temperature during a glacial period 
averaged S^'G. lower than now, as is commonly supposed, 
this part of Siberia would have had a temperature below 
freezing for at least nine months out of the twelve even if 
there were no snowfield to keep the summers cold. Yet 
even under such conditions no glaciation occurred, al- 
though in other places, such as parts of Canada and 
northwestern Europe, intense glaciation occurred where 
the mean temperature is much higher. 

The topography of the lands apparently had much 
more influence upon the localization of glaciation than 
did temperature. Its effect, however, was always to cause 
glaciation exactly where it would be expected and not in 
unexpected places as actually occurred. For example, in 
North America the western side of the Canadian Bockies 


suffered intense glaciation, for there precipitation was 
heavy because the westerly winds from the Pacific are 
forced to give up their moisture as they rise. In the same 
way the western side of the Sierra Nevadas was much 
more heavily glaciated than the eastern side. In similar 
fashion the windward slopes of the Alps, the Caucasus, 
the Himalayas, and many other mountain ranges suf- 
fered extensive glaciation. Low temperature does not 
seem to have been the cause of this glaciation, for in that 
case it is hard to see why both sides of the various ranges 
did not show an equal percentage of increase in the size 
of their icefields. 

From what has been said as to temperature and topog- 
raphy, it is evident that variations in precipitation have 
had much more to do with glaciation than have variations 
in temperature. In the Arctic lowlands and on the lee- 
ward side of mountains, the slight development of glacia- 
tion appears to have been due to scarcity of precipita- 
tion. On the windward side of mountains, on the other 
hand, a notable increase in precipitation seems to have 
led to abundant glaciation. Such an increase in precipi- 
tation must be dependent on increased evaporation and 
this could arise either from relatively high temperature 
or strong winds. Since the temperature in the glacial 
period was lower than now, we seem forced to attribute 
the increased precipitation to a strengthening of the 
winds. If the westerly winds from the Pacific should in- 
crease in strength and waft more moisture to the western 
side of the Canadian Rockies,' or if similar winds in- 
creased the snowfall on the upper slopes of the Alps or 
the Tian-Shan Mountains, the glaciers would extend 
lower than now without any change in temperature. 

Although the incompetence of low temperature to cause 
glaciation, and the relative unimportance of the moun- 


tains in northeastern Canada and northwestern Europe 
throw most glacial hypotheses out of court, they are in 
harmony with the cyclonic hypothesis. The answer of 
that hypothesis to the problem of the localization of ice 
sheets seems to be found in certain maps of storminess 
and rainfall in relation to solar activity. In Fig. 2 a 
marked belt of increased storminess at times of many 
sunspots is seen in southern Canada. A comparison of 
this with a series of maps given in Earth and Sun shows 
that the stormy belt tends to migrate northward in har- 
mony with an increase in the activity of the sun *s atmos- 
phere. If the sun were sufficiently active the belt of 
maximum storminess would apparently pass through the 
Keewatin and Labradorean centers of glaciation instead 
of well to the south of them, as at present. It would 
presumably cross another center in Greenland, and then 
would traverse the fourth of the great centers of Pleisto- 
cene glaciation in Scandinavia. It would not succeed in 
traversing northern Asia, however, any more than it 
does now, because of the great high-pressure area which 
develops there in winter. When the ice sheets expanded 
from the main centers of glaciation, the belt of storms 
would be pushed southward and outward. Thus it might 
give rise to minor centers of glaciers such as the Patri- 
cian between Hudson Bay and Lake Superior, or the 
centers in Ireland, Cornwall, Wales, and the northern 
Ural Mountains. As the main ice sheets advanced, how- 
ever, the minor centers would be overridden and the 
entire mass of ice would be merged into one vast expanse 
in the Atlantic portion of each of the two continents. 

In this connection it may be well to consider briefly the 
most recent hypothesis as to the growth and hence the 
localization of glaciation. In 1911 and more fully in 1915, 


Hobbs,* advanced the anti-cydonic hypothesis of the 
origin of ice sheets. This hypothesis has the great merit 
of focasing attention upon the fact that ice sheets are 
pronounced anti-cydonic regions of high pressure. This 
is proved by the strong outblowing winds which pre- 
vail along their margins. Such winds must, of course, be 
balanced by inward-moving winds at high levels. Abun- 
dant observations prove that such is the case. For 
example, balloons sent up by Barkow near the margin of 
the Antarctic ice sheet reveal the occurrence of inblow- 
ing winds, although they rarely occur below a height of 
9000 meters. The abundant data gathered by Guervain 
on the coast of Greenland indicate that outblowing winds 
prevail up to a height of about 4000 meters. At that 
height inblowing winds commence and increase in fre- 
quency until at an altitude of over 5000 meters they be- 
come more common than outblowing winds. It should be 
noted, however, that in both Antarctica and Greenland, 
although the winds at an elevation of less than a thousand 
meters generally blow outward, there are frequent and 
decided departures from this rule, so that *' variable 
winds'^ are quite commonly mentioned in the reports of 
expeditions and balloon soimdings. 

The undoubted anti-cyclonic conditions which Hobbs 
thus calls to the attention of scientists seem to him to 
necessitate a peculiar mechanism in order to produce 
the snow which feeds the glaciers. He assumes that the 
winds which blow toward the centers of the ice sheets 
at high levels carry the necessary moisture by which the 
glaciers grow. When the air descends in the centers of 
the highs, it is supposed to be chilled on reaching the sur- 

iW. H. Hobbs: Gharacteristics of EziBtmg Glaciers, 1911. The Bdle of 
the Glaeial Antieyclones in the Air Circulation of the Globe; Proc. Am. 
PhiL Soc., Vol. 54, 1915, pp. 185-225. 


face of the ice, and hence to give up its moisture in the 
form of minute crystals. This conclusion is doubtful for 
several reasons. In the first place, Hobbs does not seem 
to appreciate the importance of the variable winds which 
he quotes Arctic and Antarctic explorers as describing 
quite frequently on the edges of the ice sheets. They are 
one of many signs that cyclonic storms are fairly fre- 
quent on the borders of the ice though not in its interior. 
Thus there is a distinct and sufficient form of precipita- 
tion actually at work near the margin of the ice, or 
exactly where the thickness of the ice sheet would lead 
us to expect. 

Another consideration which throws grave doubt on 
the anti-cyclonic hypothesis of ice sheets is the small 
amount of moisture possible in the highs because of their 
low temperature. Suppose, for the sake of argument, 
that the temperature in the middle of an ice sheet aver- 
ages 20°F. This is probably much higher than the actual 
fact and therefore unduly favorable to the anti-cyclonic 
hypothesis. Suppose also that the decrease in tempera- 
ture from the earth ^s surface upward proceeds at the 
rate of l^'F. for each 300 feet, which is 50 per cent less 
than the actual rate for air with only a slight amount of 
moisture, such as is found in cold regions. Then at a 
height of 10,000 feet, where the inblowing winds begin 
to be felt, the temperature would be — ^20°F. At that 
temperature the air is able to hold approximately 0.166 
grain of moisture per cubic foot when fully saturated. 
This is an exceedingly small amount of moisture and even 
if it were all precipitated could scarcely build a glacier. 
However, it apparently would not be precipitated because 
when such air descends in the center of the anti-cyclone 
it is warmed adiabatically, that is, by compression. On 
reaching the surface it would have a temperature of 20° 


and would be able to hold 0.898 grain of water vapor per 
cubic foot ; in other words, it would have a relative hu- 
midity of about 18 per cent. Under no reasonable assump- 
tion does the upper air at the center of an ice sheet 
appear to reach the surface with a relative humidity of 
more than 20 or 25 per cent. Such air cannot give up 
moisture. On the contrary, it absorbs it and tends to 
diminish rather than increase the thickness of the sheet 
of ice and snow. But after the surplus heat gained by 
descent has been lost by radiation, conduction, and 
evaporation, the air may become super-saturated with 
the moisture picked up while warm. Hobbs reports that 
explorers in Antarctica and Greenland have frequently 
observed condensation on their clothing. If such moisture 
is not derived directly from the men*s own bodies, it is 
apparently picked up from the ice sheet by the descending 
air, and not added to the ice sheet by air from aloft. 

The relation of all this to the localization of ice sheets 
is this. If Hobbs' anti-cyclonic hypothesis of glacial 
growth is correct, it would appear that ice sheets should 
grow up where the temperature is lowest and the high- 
pressure areas most persistent ; for instance, in northern 
Siberia. It would also appear that so far as the topog- 
raphy permitted, the ice sheets ought to move out uni- 
formly in all directions ; hence the ice sheet ought to be 
as prominent to the north of the Keewatin and Labra- 
dorean centers as to the south, which is by no means the 
case. Again, in mountainous regions, such as the glacial 
areas of Alaska and Chile, the glaciation ought not to 
be confined to the windward slope of the mountains so 
closely as is actually the fact. In each of these cases the 
glaciated region was large enough so that there was 
probably a true anti-cyclonic area comparable with that 
now prevailing over southern Greenland. In both places 


the correlation between gladation and mountain ranges 
seems much too close to support the anti-cyclonic hy- 
pothesis, for the inblowing winds which on that hypothe- 
sis bring the moisture are shown by observation to occur 
at heights far greater than that of all but the loftiest 

II. The sudden coming of glaciation is another prob- 
lem which has been a stumbling-block in the way of every 
glacial hypothesis. In his Climates of Geologic Times, 
Schuchert states that the fossils give almost no warning 
of an approaching catastrophe. If glaciation were solely 
due to uplift, or other terrestrial changes aside from vul- 
canism, Schuchert holds that it would have come slowly 
and the stages preceding glaciation would have affected 
life sufficiently to be recorded in the rocks. He considers 
that the suddenness of the coming of glaciation is one 
of the strongest arguments against the carbon dioxide 
hypothesis of glaciation. 

According to the cyclonic hypothesis, however, the 
suddenness of the oncoming of glaciation is merely what 
would be expected on the basis of what happens today. 
Changes in the sun occur suddenly. The sunspot cycle is 
only eleven or twelve years long, and even this short 
period of activity is inaugurated more suddenly than it 
declines. Again the climatic record derived from the 
growth of trees, as given in Figs. 4 and 5, also shows that 
marked changes in climate are initiated more rapidly 
than they disappear. In tiiis connection, however, it must 
be remembered that solar activity may arise in various 
ways, as will appear more fully later. Under certain con- 
ditions storminess may increase and decrease slowly. 

III. The height of the snow line and of glaciation fur- 
nishes another means of testing glacial hypotheses. It is 
well established that in times of glaciation the snow line 


was depressed everywhere, but least near the equator. 
For example, according to Penck, permanent snow ex- 
tended 4000 feet lower than now in the Alps, whereas 
it stood only 1500 feet below the present level near the 
equator in Venezuela. This unequal depression is not 
readily accounted for by any hypothesis depending solely 
upon the lowering of temperature. By the carbon dioxide 
and the volcanic dust hypotheses, the temperature pre- 
sumably was lowered amost equally in all latitudes, but 
a little more at the equator than elsewhere. If glaciation 
were due to a temporary lessening of the radiation re- 
ceived from the sun, such as is demanded by the thermal 
solar hypothesis, and by the longer periods of CrolPs 
hypothesis, the lowering would be distinctly greatest at 
the equator. Thus, according to all these hypotheses, the 
snow line should have been depressed most at the equator, 
instead of least. 

The cyclonic hypothesis explains the lesser depression 
of the snow line at the equator as due to a diminution of 
precipitation. The effectiveness of precipitation in this 
respect is illustrated by the present great difference in 
the height of the snow line on the humid and dry sides of 
mountains. On the wet eastern side of the Andes near the 
equator, the snow line lies at 16,000 feet; on the dry 
western side, at 18,500 feet. Again, although the humid 
side of the Himalayas lies toward the south, the snow line 
has a level of 15,000 feet, while farther north, on the dry 
side, it is 16,700 feet.* The fact that the snow line is lower 
near the margin of the Alps than toward the center 
points in the same direction. The bearing of all this on 
the glacial period may be judged by looking again at Fig. 
3 in Chapter V. This shows that at times of sunspot 
activity and hence of augmented storminess, the precipir 

SB. D. Salisbary: Physiographj, 1919. 


tation diminishes near the heat equator, that is, where 
the average temperature for the whole year is highest. 
At present the great size of the northern continents and 
their consequent high temperature in summer, cause the 
heat equator to lie north of the **real" equator, except 
where Australia draws it to the southward.* When large 
parts of the northern continents were covered with ice, 
however, the heat equator and the true equator were 
probably much closer than now, for the continents could 
not become so hot. If so, the diminution in equatorial 
precipitation, which accompanies increased storminess 
throughout the world as a whole, would take place more 
nearly along the true equator than appears in Fig. 3. 
Hence so far as precipitation alone is concerned, we 
should actually expect that the snow line near the equator 
would rise a little during glacial periods. Another factor, 
however, must be considered. Koppen's data, it will be 
remembered, show that at times of solar activity the 
earth's temperature falls more at the equator than in 
higher latitudes. If this effect were magnified it would 
lower the snow line. The actual position of the snow line 
at the equator during glacial periods thus appears to be 
the combined effect of diminished precipitation, which 
would raise the line, and of lower temperature, which 
would bring it down. 

Before leaving this subject it may be well to recall that 
the relative lessening of precipitation in equatorial lati- 
tudes during the glacial epochs was probably caused by 
the diversion of moisture from the trade-wind belt. This 
diversion was presumably due to the great number of 
tropical cyclones and to the fact that the cyclonic storms 
of middle latitudes also drew much moisture from the 
trade-wind belt in summer when the northern position of 

s Griffith Taylor: Australian Meteorology^ 1920, p. 283. 


the sun drew that belt near the storm track which was 
forced to remain south of the ice sheet. Such diversion 
of moisture out of the trade-wind belt must diminish the 
amount of water vapor that is carried by the trades to 
equatorial regions; hence it would lessen precipitation 
in the belt of so-called equatorial calms, which lies along 
the heat equator rather than along the geographical 

Another phase of the vertical distribution of glaciation 
has been the subject of considerable discussion. In the 
Alps and in many other mountains the glaciation of the 
Pleistocene period appears to have had its upper limit 
no higher than today. This has been variously inter- 
preted. It seems, however, to be adequately explained 
as due to decreased precipitation at high altitudes during 
the cold periods. This is in spite of the fact that precipi- 
tation in general increased with increased storminess. 
The low temperature of glacial times presimiably induced 
condensation at lower altitudes than now, and most of 
the precipitation occurred upon the lower slopes of the 
mountains, contributing to the lower glaciers, while little 
of it fell upon the highest glaciers. Above a moderate 
altitude in all lofty mountains the decrease in the amount 
of precipitation is rapid. In most cases the decrease 
begins at a height of less than 3000 feet above the base 
of the main slope, provided the slope is steep. The colder 
the air, the lower the altitude at which this occurs. For 
example, it is much lower in winter than in summer. 
Indeed, the higher altitudes in the Alps are sunny in 
winter even where there are abundant clouds lower down. 

IV. The presence of extensive lakes and other evidences 
of a pluvial climate during glacial periods in non-glaci- 
ated regions which are normally dry is another of the 
facts which most glacial hypotheses fail to explain satis- 


the region of salt lakes in the Old World. Judging by 
these maps, which illustrate what has happened since 
careful meteorological records were kept, an increase in 
solar activity is accompanied by increased rainfall in 
large parts of what are now semi-arid and desert regions. 
Such precipitation would at once cause the level of the 
lakes to rise. Later, when ice sheets had developed in 
Europe and America, the high-pressure areas thus caused 
might force the main storm belt so far south that it would 
lie over these same arid regions. The increase in tropical 
hurricanes at times of abundant sunspots may also have 
a bearing on the climate of regions that are now arid. 
During the glacial period some of the hurricanes prob- 
ably swept far over the lands. The numerous tropical 
cyclones of Australia, for example, are the chief source 
of precipitation for that continent." Some of the stronger 
cyclones locally yield more rain in a day or two than 
other sources yield in a year. 

V. The occurrence of widespread glaciation near the 
tropics during the Permian, as shown in Fig. 7, has given 
rise to much discussion. The recent discovery of glacia- 
tion in latitudes as low as 30° in the Proterozoic is corre- 
spondingly significant. In all cases the occurrence of 
glaciation in low and middle latitudes is probably due to 
the same general causes. Doubtless the position and alti- 
tude of the mountains had something to do with the 
matter. Yet taken by itself this seems insufficient. Today 
the loftiest range in the world, the Himalayas, is almost 
unglaciated, although its southern slope may seem at first 
thought to be almost ideally located in this respect. Some 
parts rise over 20,000 feet and certain lower slopes re- 
ceive 400 inches of rain per year. The small size of the 
Himalayan glaciers in spite of these favorable conditions 

10 Griffith Taylor: Australian Meteorology, 1920, p. 189. 


is apparently due largely to the seasonal character of tlie 
monsoon winds. The strong ontblowing monsoons of 
winter cause about half the year to be very dry with clear 
skies and dry winds from the interior of Asia. In aU low 
latitudes the sun rides high in the heavens at midday, 
even in winter, and thus melts snow fairly effectively in 
clear weather. This is highly unfavorable to glaciatioiu 
The inblowing southern monsoons bring all their mois- 
ture in midsummer at just the time when it is least effec- 
tive in producing snow. Conditions similar to those now- 
prevailing in the Himalayas must accompany any great 
uplift of the lands which produces high mountains and 
large continents in subtropical and middle latitudes. 
Hence, uplift alone cannot account for extensive glacia- 
tion in subtropical latitudes during the Permian and 

The assumption of a great general lowering of tem- 
perature is also not adequate to explain glaciation in 
subtropical latitudes. In the first place this would reqtdre 
a lowering of many degrees, — ^far more than in the Pleis- 
tocene glacial period. The marine fossils of the Permian, 
however, do not indicate any such condition. In the 
second place, if the lands were widespread as they ap- 
pear to have been in the Permian, a general lowering of 
temperature would diminish rather than increase the 
present slight efficiency of the monsoons in producing 
glaciation. Monsoons depend upon the difference between 
the temperatures of land and water. If the general tem- 
perature were lowered, the reduction would be much less 
pronounced on the oceans than on the lands, for water 
tends to preserve a uniform temperature, not only be- 
cause of its mobility, but because of the large amount of 
heat given out when freezing takes place, or consumed in 
evaporation. Hence the general lowering of temperature 


would make the contrast between continents and oceans 
less than at present in summer, for the land temperature 
would be brought toward that of the ocean. This would 
diminish the strength of the inblowing summer mon- 
soons and thus cut off part of the supply of moisture. 
Evidence thjat this actually happened in the cold four- 
teenth century has already been given in Chapter VI. 
On the other hand, in winter the lands would be much 
colder than now and the oceans only a little colder, so 
that the dry outblowing monsoons of the cold season 
would increase in strength and would also last longer 
than at present. In addition to all this, the mere fact of 
low temperature would mean a general reduction in the 
amount of water vapor in the air. Thus, from almost 
every point of view a mere lowering of temperature 
seems to be ruled out as a cause of Permian glaciation. 
Moreover, if the Permian or Proterozoic glacial periods 
were so cold that the lands above latitude 30*^ were snow- 
covered most of the time, the normal surface winds in 
subtropical latitudes would be largely equatorward, just 
as the winter monsoons now are. Hence little or no mois- 
ture would be available to feed the snowfields which give 
rise to the glaciers. 

It has been assumed by Marsden Manson and others 
that increased general cloudiness would account for the 
subtropical glaciation of the Permian and Proterozoic. 
Granting for the moment that there could be universal 
persistent cloudiness, this would not prevent or counter- 
act the outblowing anti-cyclonic winds so characteristic 
of great snowfields. Therefore, under the hypothesis of 
general cloudiness there would be no supply of moisture 
to cause glaciation in low latitudes. Indeed, persistent 
cloudiness in all higher latitudes would apparently de- 
prive the Himalayas of most of their present moisture. 


for the interior of Asia would not become hot in summer 
and no inblowing monsoons would develop. In fact, winds 
of all kinds would seemingly be scarce, for they arise 
almost wholly from contrasts of temperature and hence 
of atmospheric pressure. The only way to get winds and 
hence precipitation would be to invoke some other agency, 
such as cyclonic storms, but that would be a departure 
from the supposition that glaciation arose from cloudi- 

Let us now inquire how the cyclonic hypothesis 
accounts for glaciation in low latitudes. We will first 
consider the terrestrial conditions in the early Permian, 
the last period of glaciation in such latitudes. Geologists 
are almost universally agreed that the lands were excep- 
tionally extensive and also high, especially in low lati- 
tudes. One evidence of this is the presence of abundant 
conglomerates composed of great boulders. It is also 
probable that the carbon dioxide in the air during the 
early Permian had been reduced to a minimum by the 
extraordinary amount of coal formed during the preced- 
ing period. This would tend to produce low temperature 
and thus make the conditions favorable for glaciation as 
soon as an accentuation of solar activity caused unusual 
storminess. If the storminess became extreme when ter- 
restrial conditions were thus universally favorable to 
glaciation, it would presumably produce glaciation in low 
latitudes. Numerous and intense tropical cyclones would 
carry a vast amount of moisture out of the tropics, just 
as now happens when the sun is active, but on a far 
larger scale. The moisture would be precipitated on the 
equatorward slopes of the subtropical mountain ranges. 
At high elevations this precipitation would be in the form 
of snow even in summer. Tropical cyclones, however, as 
is shown in Earth and Sun, occur in the autumn and 


winter as well as in summer. For example, in the Bay of 
Bengal the number recorded in October is fifty, the 
largest for any month; while in November it is thirty- 
f onr, and December fourteen as compared with an aver- 
age of forty-two for the months of July to September. 
From January to March, when sunspot numbers aver- 
aged more than forty, the number of tropical hurricanes 
was 143 per cent greater than when the sunspot numbers 
averaged below forty. During the months from April to 
June, which also would be times of considerable snowy 
precipitation, tropical hurricanes averaged 58 per cent 
more numerous with sunspot niunbers above forty than 
with numbers below forty, while from July to September 
the difference amounted to 23 per cent. Even at this 
season some snow falls on the higher slopes, while the 
increased cloudiness due to numerous storms also tends 
to preserve the snow. Thus a great increase in the fre- 
quency of sunspots is accompanied by increased intensity 
of tropical hurricanes, especially in the cooler autumn and 
spring months, and results not only in a greater accumu- 
lation of snow but in a decrease in the melting of the 
snow because of more abundant clouds. At such times as 
the Permian, the general low temperature due to rapid 
convection and to the scarcity of carbon dioxide pre- 
sumably joined with the extension of the lands in pro- 
ducing great high-pressure areas over the lands in middle 
latitudes during the winters, and thus caused the more 
northern, or mid-latitude type of cyclonic storms to be 
shifted to the equatorward side of the continents at that 
season. This would cause an increase of precipitation in 
winter as well as during the months when tropical hurri- 
canes abound. Many other circumstances would cooper- 
ate to produce a sunilar result. For example, the general 
low temperature would cause the sea to be covered with 


ice in lower latitudes than now, and would help to create 
high-pressure areas in middle latitudes, thus driving the 
storms far south. If the sea water were fresher than now, 
as it probably was to a notable extent in the Proterozoic 
and perhaps to some slight extent in the Permian, the 
higher freezing point would also further the extension 
of the ice and help to keep the storms away from high 
latitudes. If to this there is added a distribution of land 
and sea such that the volume of the warm ocean currents 
flowing from low to high latitudes was diminished, as 
appears to have been the case, there seems to be no diffi- 
culty in explaining the subtropical location of the main 
glaciation in both the Permian and the Proterozoic. An 
increase of storminess seems to be the key to the whole 

One other possibility may be mentioned, although little 
stress should be laid on it. In Earth and Sun it has been 
shown that the main storm track in both the northern 
and southern hemispheres is not concentric with the 
geographical poles. Both tracks are roughly concentric 
with the corresponding magnetic poles, a fact which-may 
be important in connection with the hypothesis of an elec- 
trical effect of the sun upon terrestrial storminess. The 
magnetic poles are known to wander considerably. Such 
wandering gives rise to variations in the direction of 
the magnetic needle from year to year. In 1815 the com- 
pass in England pointed 241/2° W. of N. and in 1906 
17° 45' W. Such a variation seems to mean a change of 
many miles in the location of the north magnetic pole. 
Certain changes in the daily march of electromagnetic 
phenomena over the oceans have led Bauer and his asso- 
ciates to suggest that the magnetic poles may even be 
subject to a slight daily movement in response to the 
changes in the relative positions of the earth and sun. 


Thus there seems to be a possibility that a pronounced 
change in the location of the magnetic pole in Permian 
times, for example, may have had some connection with 
a shifting in the location of the belt of storms. It must be 
clearly understood that there is as yet no evidence of any 
such change, and the matter is introduced merely to call 
attention to a possible line of investigation. 

Any hypothesis of Permian and Proterozoic gladation 
must explain not only the glaciation of low latitudes but 
the lack of glaciation and tiie accumulation of red desert 
beds in high latitudes. The facts already presented seem 
to explain this. Glaciation could not occur extensively in 
high latitudes partly because during most of the year the 
air was too cold to hold much moisture, but still more 
because the winds for the most part must have blown 
outward from the cold northern areas and the cyclonic 
storm belt was pushed out of high latitudes. Because of 
these conditions precipitation was apparently limited to 
a relatively small number of storms during the smnmer. 
Hence great desert areas must have prevailed at high 
latitudes. Great aridity now prevails north of the Hima- 
layas and related ranges, and red beds are accumulating 
in the centers of the great deserts, such as those of the 
Tarim Basin and the Transcaspian. The redness is not 
due to the original character of the rock, but to intense 
oxidation, as appears from the fact that along the edges 
of the desert and wherever occasional floods carry sedi- 
ment far out into the midst of the sand, the material has 
the ordinary brownish shades. As soon as one goes out 
into the places where the sand has been exposed to the air 
for a long time, however, it becomes pink, and then red. 
Such conditions may have given rise to the high degree 
of oxidation in the famous Permian red beds. If the air 
of the early Permian contained an unusual percentage of 


oxygen because of the release of that gas by the great 
plant beds which formed coal in the preceding era, as 
Chamberlin has thought probable, the tendency to pro- 
duce red beds would be still further increased. 

It must not be supposed, however, that these condi- 
tions would absolutely limit glaciation to subtropical 
latitudes. The presence of early Permian glaciation in 
North America at Boston and in Alaska and in the Falk- 
land Islands of the South Atlantic Ocean proves that at 
least locally there was sufficient moisture to form glaciers 
near the coast in relatively high latitudes. The possibility 
of this would depend entirely upon the form of the lands 
and the consequent course of ocean currents. Even in 
those high latitudes cyclonic storms would occur unless 
they were kept out by conditions of pressure such as have 
been described above. 

The marine faunas of Permian age in high latitudes 
have been interpreted as indicating mild oceanic tempera- 
tures. This is a point which requires further investiga- 
tion. Warm oceans during times of slight solar activity 
are a necessary consequence of the cyclonic hypothesis, 
as will appear later. The present cold oceans seem to be 
the expectable result of the Pleistocene glaciation and of 
the present relatively disturbed condition of the sun. If 
a sudden disturbance threw the solar atmosphere into 
violent commotion within a few thousand years during 
Permian times, glaciation might occur as described above, 
while the oceans were still warm. In fact their warmth 
would increase evaporation while the violent cyclonic 
storms and high winds would cause heavy rain and keep 
the air cool by constantly raising it to high levels where 
it would rapidly radiate its heat into space. 

Nevertheless it is not yet possible to determine how 
warm the oceans were at the actual time of the Permian 


glaciation. Some faunas formerly reported as Permian 
are now known to be considerably older. Moreover, others 
of undoubted Permian age are probably not strictly con- 
temporaneous with the glaciation. So far back in the 
geological record it is very doubtful whether we can date 
fossils within the limits of say 100,000 years. Yet a dif- 
ference of 100,000 years would be more than enough to 
allow the fossils to have lived either before or after the 
glaciation, or in an inter-glacial epoch. One such epoch 
is known to have occurred and nine others are suggested 
by the inter-stratification of glacial till and marine sedi- 
ments in eastern Australia. The warm currents which 
would flow poleward in inter-glacial epochs must have 
favored a prompt reintroduction of marine faunas driven 
out during times of glaciation. Taken all and all, the 
Permian glaciation seems to be accounted for by the 
cyclonic hypothesis quite as well as does the Pleistocene. 
In both these cases, as weU as in the various pulsations 
of historic times, it seems to be necessary merely to mag- 
nify what is happening today in order to reproduce the 
conditions which prevailed in the past. If the conditions 
which now prevail at times of sunspot minima were mag- 
nified, they would give the mild conditions of inter-glacial 
epochs and similar periods. If the conditions which now 
prevail at times of sunspot maxima are magnified a little 
they seem to produce periods of climatic stress such as 
those of the fourteenth century. If they are magnified 
still more the result is apparently glacial epochs like 
those of the Pleistocene, and if they are magnified to a 
still greater extent, the result is Permian or Proterozoic 
glaciation. Other factors must indeed be favorable, for 
climatic changes are highly complex and are unques- 
tionably due to a combination of circumstances. The point 
which is chiefly emphasized in this book is that among 


those several circumstances, changes in cyclonic storms 
due apparently to activity of the snn's atmosphere must 
always be reckoned. 


ONE of the most remarkable formations associ- 
ated with glacial deposits consists of vast sheets 
of the fine-grained, yellowish, wind-blown ma- 
terial called loess. Somewhat peculiar climatic condi- 
tions evidently prevailed when it was formed. At present 
similar deposits are being laid down only near the lee- 
ward margin of great deserts. The famous loess deposits 
of China in the lee of the Desert of Gobi are examples. 
During the Pleistocene period, however, loess accumu- 
lated in a broad zone along the margin of the ice sheet 
at its maximum extent. In the Old World it extended 
from France across Germany and through the Black 
Earth region of Russia into Siberia. In the New World 
a still larger area is loess-covered. In the Mississippi 
Valley, tens of thousands of square miles are mantled by 
a layer exceeding twenty feet in thickness and in many 
places approaching a hundred feet. Neither the North 
American nor the European deposits are associated with 
a desert. Indeed, loess is lacking in the western and 
drier parts of the great plains and is best developed in 
the well-watered states of Iowa, Illinois, and Missouri. 
Part of the loess overlies the non-glacial materials of the 
great central plain, but the northern portions overlie the 
drift deposits of the first three glaciations. A few traces 
of loess are associated with the Kansan and Illinoian, 
the second and third glaciations, but most of the Ameri- 



can loess appears to have been formed at approximately 
the time of the lowan or fourth glaciation, while only a 
little overlies the drift sheets of the Wisconsin age. The j 

loess is thickest near the margin of the lowan till sheet 
and thins progressively both north and south. The 
thinning southward is abrupt along the stream divides, 
but very gradual along the larger valleys. Indeed, loess is 
abundant along the bluffs of the Mississippi, especially 
the east bluff, almost to the Gulf of Mexico.^ 

It is now generally agreed that all typical loess is wind 
blown. There is still much question, however, as to its 
time of origin, and thus indirectly as to its climatic im- 
plications. Several American and European students 
have thought that the loess dates from inter-glacial times. 
On the other hand, Penck has concluded that the loess 
was formed shortly before the commencement of the 
glacial epochs ; while many American geologists hold that 
the loess accumulated while the ice sheets were at ap- 
proximately their maximum size. W. J. McGee, Cham- 
berlin and Salisbury, Keyes, and others lean toward this 
view. In this chapter the hypothesis is advanced that it 
was formed at the one other possible time, namely, imme- 
diately following the retreat of the ice. 

These four hypotheses as to the time of origin of loess 
imply the following differences in its climatic relations. 
If loess was formed during typical inter-glacial epochs, 
or toward the close of such epochs, profound general 
aridity must seemingly have prevailed in order to kill 
off the vegetation and thus enable the wind to pick up 
sufficient dust. If the loess was formed during times of 
extreme glaciation when the glaciers were supplying 
large quantities of fine material to outflowing streams, 
less aridity would be required, but there must have been 

1 Chamberlin and Salisbury: Geology, 1906^ Vol. Ill, pp. 405-412. 


sharp contrasts between wet seasons in summer when 
the snow was melting and dry seasons in winter when 
the storms were forced far south by the glacial high pres- 
sare. Alternate floods and droughts would thus affect 
broad areas along the streams. Hence arises the hypothe- 
sis that the wind obtained the loess from the flood plains 
of streams at times of maximum glaciation. If the loess 
was formed during the rapid retreat of the ice, alternate 
summer floods and winter droughts would still prevail, 
but much material could also be obtained by the winds 
not only from flood plains, but also from the deposits 
exposed by the melting of the ice and not yet covered by 

The evidence for and against the several hypotheses 
may be stated briefly. In support of the hypothesis of the 
inter-glacial origin of loess, Shimek and others state that 
the glacial drift which lies beneath the loess commonly 
gives evidence that some time elapsed between the dis- 
appearance of the ice and the deposition of the loess. For 
example, abundant shells of land snails in the loess are 
not of the sort now found in colder regions, but resemble 
those found in the drier regions. It is probable that if 
they represented a glacial epoch they would be depauper- 
ated by the cold as are the snails of far northern regions. 
The gravel pavement discussed below seems to be strong 
evidence of erosion between the retreat of the ice and 
the deposition of the loess. 

Turning to the second hypothesis, namely, that the 
loess accumulated near the close of the inter-glacial epoch 
rather than in the midst of it, we may follow Penck. The 
mammalian fossils seem to him to prove that the loess 
was formed while boreal animals occupied the region, for 
they include remains of the hairy manmaoth, woolly rhi- 
noceros, and reindeer. On the other hand, the typical 


inter-glacial beds not far away yield remains of species 
characteristic of milder climates, such as the elephant, 
the smaller rhinoceros, and the deer. In connection with 
these facts it should be noted that occasional remains of 
tundra vegetation and of trees are found beneath the 
loess, while in the loess itself certain steppe animals, 
such as the common gopher or spermaphyl, are found. 
Penck interprets this as indicating a progressive desicca- 
tion culminating just before the oncoming of the next ice 

The evidence advanced in favor of the hypothesis that 
the loess was formed when glaciation was Sar its maxi- 
mum includes the fact that if the loess does not represent 
the outwash from the lowan ice, there is little else that 
does, and presumably there must have been outwash. 
Also the distribution of loess along the margins of 
streams suggests that much of the material came from 
the flood plains of overloaded streams flowing from the 
melting ice. 

Although there are some points in favor of the hy- 
pothesis that the loess originated (1) in strictly inter- 
glacial times, (2) at the end of inter-glacial epochs, and 
(3) at times of full glaciation, each hypothesis is much 
weakened by evidence that supports the others. The evi- 
dence of boreal animals seems to disprove the hypothesis 
that the loess was formed in the middle of a mild inter- 
glacial epoch. On the other hand, Penck 's hypothesis as 
to loess at the end of inter-glacial times fails to account 
for certain characteristics of the lowest part of the loess 
deposits and of the underlying topography. Instead of 
normal valleys and consequent prompt drainage such as 
ought to have developed before the end of a long inter- 
glacial epoch, the surface on which the loess lies shows 
many undrained depressions. Some of these can be seen 


in exposed banks, while many more are inferred from the 
presence of shells of pond snails here and there in the 
overlying loess. The pond snails presumably lived in 
shallow pools occupying depressions in the uneven sur- 
face left by the ice. Another reason for questioning 
whether the loess was formed at the end of an inter- 
glacial epoch is that this hypothesis does not provide a 
reasonable origin for the material which composes the 
loess. Near the Alps where the loess deposits are small 
and where glaciers probably persisted in the inter-glacial 
epochs and thus supplied flood plaia material in large 
quantities, this does not appear important. In the broad 
upper Mississippi Basin, however, and also in the Black 
Earth region of Russia there seems to be no way to get 
the large body of material composing the loess except by 
assuming the existence of great deserts to windward. 
But there seems to be little or no evidence of such deserts 
where they could be effective. The mineralogical char- 
acter of the loess of lowan age proves that the material 
came from granitic rocks, such as formed a large part of 
the drift. The nearest extensive outcrops of granite are 
in the southwestern part of the United States, nearly a 
thousand miles from Iowa and Illinois. But the loess is 
thickest near the ice margin and thins toward the south- 
west and in other directions, whereas if its source were 
the southwestern desert, its maximum thickness would 
probably be near the margin of the desert. 

The evidence cited above seems inconsistent not only 
with the hypothesis that the loess was formed at the end 
of an inter-glacial epoch, but also with the idea that it 
originated at times of maximum glaciation either from 
river-borne sediments or from any other source. A 
further and more convincing reason for this last con- 
clusion is the probability and almost the certainty that 


when the ice advanced, its front lay close to areas where 
the vegetation was not much thinner than that which 
today prevails under similar climatic conditions. If the 
average temperature of glacial maxima was only 6°G. 
lower than that of today, the conditions just beyond the 
ice front when it was in the loess region from southern 
Illinois to Minnesota would have been like those now pre- 
vailing in Canada from New Brunswick to Winnipeg. 
The vegetation there is quite different from the grassy, 
semi-arid vegetation of which evidence is found in the 
loess. The roots and stalks of such grassy vegetation are 
generally agreed to have helped produce the columnar 
structure which enables the loess to stand with almost 
vertical surfaces. 

We are now ready to consider the probability that loess 
accumulated mainly during the retreat of the ice. Such a 
retreat exposed a zone of drift to the outflowing glacial 
winds. Most glacial hypotheses, such as that of uplift, 
or depleted carbon dioxide, call for a gradual retreat 
of the ice scarcely faster than the vegetation could ad- 
vance into the abandoned area. Under the solar-cyclonic 
hypothesis, on the other hand, the climatic changes may 
have been sudden and hence the retreat of the ice may 
have been much more rapid than the advance of vegeta- 
tion. Now wind-blown materials are derived from places 
where vegetation is scanty. Scanty vegetation on good 
soil, it is true, is usually due to aridity, but may also 
result because the time since the soil was exposed to the 
air has not been long enough for the soil to be sufficiently 
weathered to support vegetation. Even when weathering 
has had full opportunity, as when sand bars, mud flats, 
and flood plains are exposed, vegetation takes root only 
slowly. Moreover, storms and violent winds may prevent 
the spread of vegetation, as is seen on sandy beaches even 


in distinctly humid regions like New Jersey and Den- 
mark. Thus it appears that unless the retreat of the ice 
were as slow as the advance of vegetation, a barren area 
of more or less width must have bordered the retreating 
ice and formed an ideal source of loess. 

Several other lines of evidence seemingly support the 
conclusion that the loess was formed during the retreat 
of the ice. For example, Shimek, who has made almost 
a lifelong study of the lowan loess, emphasizes the fact 
that there is often an accumulation of stones and pebbles 
at its base. This suggests that the underlying till was 
eroded before the loess was deposited upon it. The first 
reaction of most students is to assume that of coui'se 
this was due to running water. That is possible in many 
cases, but by no means in all. So widespread a sheet of 
gravel could not be deposited by streams without destroy*- 
ing the irregular basins and hollows of which we have 
seen evidence where the loess lies on glacial deposits. On 
the other hand, the wind is competent to produce a simi*- 
lar gravel pavement without disturbing the old topog- 
raphy. ** Desert pavements'' are a notable feature in most 
deserts. On the edges of an ice sheet, as Hobbs has made 
us realize, the commonest winds are outward. They often 
attain a velocity of eighty miles an hour in Antarctica 
and Greenland. Such winds, however, usually decline 
rapidly in velocity only a few score miles from the ice. 
Thus their effect would be to produce rapid erosion 
of the freshly bared surface near the retreating ice. 
The pebbles would be left behind as a pavement, while 
sand and then loess would be deposited farther from the 
ice where the winds were weaker and where vegetation 
was beginning to take root. Such a decrease in wind 
velocity may explain the occasional vertical gradation 
from gravel through sand to coarse loess and then to 


normal fine loess. As the ice sheet retreated the wind in 
any given place would gradually become less violent. 
As the ice continued to retreat the area where loess was 
deposited would follow at a distance, and thus each part 
of the gravel pavement would in turn be covered with the 

The hypothesis that loess is deposited while the ice is 
retreating is in accord with many other lines of evidence. 
For example, it accords with the boreal character of the 
mammal remains as described above. Again, the advance 
of vegetation into the barren zone along the front of the 
ice would be delayed by the strong outblowing winds. 
The common pioneer plants depend largely on the wind 
for the distribution of their seeds, but the glacial winds 
would carry them away from the ice rather than toward 
it. The glacial winds discourage the advance of vegeta- 
tion in another way, for they are drying winds, as are 
almost all winds blowing from a colder to a warmer 
region. The fact that remains of trees sometimes occur 
at the bottom of the loess probably means that the depo- 
sition of loess extended into the forests which almost 
certainly persisted not far from the ice. This seems more 
likely than that a period of severe aridity before the ad- 
vance of the ice killed the trees and made a steppe or 
desert. Penck's chief argument in favor of the formation 
of loess before the advance of the ice rather than after, 
is that since loess is lacking upon the youngest drift sheet 
in Europe it must have been formed before rather than 
after the last or Wiirm advance of the ice. This breaks 
down on two counts. First, on the corresponding (Wis- 
consin) drift sheet in America, loess is present, — ^in small 
quantities to be sure, but unmistakably present. Second, 
there is no reason to assume that conditions were identi- 
cal at each advance and retreat of the ice. Indeed, the 


fact that in Europe, as in the United States, nearly all 
the loess was formed at one time, and only a little is asso- 
ciated with the other ice advances, points clearly against 
Penck's fundamental assumption that the accumulation 
of loess was due to the approach of a cold climate. 

Having seen that the loess was probably formed during 
the retreat of the ice, we are now ready to inquire what 
conditions the cyclonic hypothesis would postulate in the 
loess areas during the various stages of a glacial cycle. 
Fig. 2, in Chapter IV, gives the best idea of what would 
apparently happen in North America, and events in Europe 
would presumably be similar. During the nine maximmn 
years on which Fig. 2 is based the sunspot numbers aver- 
aged seventy, while during the nine minimum years they 
averaged less than five. It seems fair to suppose that the 
maximum years represent the average conditions which 
prevailed in the past at times when the sun was in a 
median stage between the full activity which led to glacia- 
tion and the mild activity of the minimum years which 
appear to represent inter-glacial conditions. This would 
mean that when a glacial period was approaching, but 
before an ice sheet had accumulated to any great extent, 
a crescent-shaped strip from Montana through Illinois to 
Maine would suffer a diminution in storminess ranging 
up to 60 per cent as compared with inter-glacial condi- 
tions. This is in strong contrast with an increase in 
storminess amounting to 75 or even 100 per cent both in 
the boreal storm belt in Canada and in the subtropical 
belt in the Southwest. Such a decrease in storminess in 
the central United States would apparently be most 
noticeable in summer, as is shown in Earth and Sun. 
Hence it would have a maximum effect in producing 
aridity. This would favor the formation of loess, but it is 
doubtful whether the aridity would become extreme 


enough to explain such vast deposits as are found 
throughout large parts of the Mississippi Basin. That 
would demand that hundreds of thousands of square miles 
should become almost absolute desert, and it is not prob- 
able that any such thing occurred. Nevertheless, accord- 
ing to the cyclonic hypothesis the period inmiediately 
before the advent of the ice would be relatively dry in 
the central United States, and to that extent favorable to 
the work of the wind. 

As the climatic conditions became more severe and the 
ice sheet expanded, the dryness and lack of storms would 
apparently diminish. The reason, as has been explained, 
would be the gradual pushing of the storms southward 
by the high-pressure area which would develop over the 
ice sheet. Thus at the height of a glacial epoch there 
would apparently be great storminess in the area where 
the loess is found, especially in sunmaer. Hence the 
cyclonic hypothesis does not accord with the idea of great 
deposition of loess at the time of maximum glaciation. 

Finally we come to the time when the ice was retreat- 
ing. We have already seen that not only the river flood 
plains, but also vast areas of fresh glacial deposits would 
be exposed to the winds, and would remain without vege- 
tation for a long time. At that very time the retreat of 
the ice sheet would tend to permit the storms to follow 
paths determined by the degree of solar activity, in place 
of the far southerly paths to which the high atmospheric 
pressure over the expanded ice sheet had previously 
forced them. In other words, the conditions shown in 
Fig. 2 would tend to reappear when the sun^s activity 
was diminishing and the ice sheet was retreating, just as 
they had appeared when the sun was becoming more 
active and the ice sheet was advancing. This time, how- 
ever, the semi-arid conditions arising from the scarcity 


of storms would prevail in a region of glacial deposits 
and widely spreading river deposits, few or none of 
which would be covered with vegetation. The conditions 
would be almost ideal for eolian erosion and for the 
transportation of loess by the wind to areas a little more 
remote from the ice where grassy vegetation had made a 

The cyclonic hypothesis also seems to offer a satis- 
factory explanation of variations in the amount of loess 
associated with the several glacial epochs. It attributes 
these to differences in the rate of disappearance of the 
ice, which in turn varied with the rate of decline of solar 
activity and storminess. This is supposed to be the reason 
why the lowan loess deposits are much more extensive 
than those of the other epochs, for the lowan ice sheet 
presumably accomplished part of its retreat much more 
suddenly than the other ice sheets.* The more sudden the 
retreat, the greater the barren area where the winds 
could gather fine bits of dust. Tempoirary readvances may 
also have been so distributed and of such intensity that 
they frequently accentuated the condition shown in Fig. 
2, thus making the central United States dry soon after 
the exposure of great amounts of glacial debris. The 
closeness with which the cyclonic hypothesis accords with 
the facts as to the loess is one of the pleasant surprises of 
the hypothesis. The first draft of Fig. 2 and the first out- 
lines of the hypothesis were framed without thought of 
the loess. Yet so far as can now be seen, both agree 
closely with the conditions of loess formation. 

sit maj have retreated soon after reaching its mazimnm. If so, the 
general lack of thick terminal moraines would be explained. See page 122. 


IN discussions of climate, as of most subjects, a 
peculiar psychological phenomenon is observable. 
Everyone sees the necessity of explaining conditions 
different from those that now exist, but few realize that 
present conditions may be abnormal, and that they need 
explanation just as much as do others. Because of this 
tendency glaciation has been discussed with the greatest 
fullness, while there has been much neglect not only of 
the periods when the climate of the earth resembled that 
of the present, but also of the vastly longer periods when 
it was even milder than now. 

How important the periods of mild climate have been 
in geological times may be judged from the relative 
length of glacial compared with inter-glacial epochs, and 
still more from the far greater relative length of the mild 
parts of periods and eras when compared with the severe 
parts. Recent estimates by R. T. Chamberlin^ indicate 
that according to the consensus of opinion among geolo- 
gists the average inter-glacial epoch during the Pleisto- 
cene was about five times as long as the average glacial 
epoch, while the whole of a given glacial epoch averaged 
five times as long as the period when the ice was at a 
maximum. Climatic periods far milder, longer, and more 
monotonous than any inter-glacial epoch appear repeat- 

1 BoUin T. Ghamberlin : Personal Communication. 


edly during the course of geological history. Our task in 
this chapter is to explain them. 

Knowlton^ has done geology a great service by col- 
lecting the evidence as to the mild type of climate which 
has again and again prevailed in the past. He lays special 
stress on botanical evidence since that pertains to the 
variable atmosphere of the lands, and hence furnishes a 
better guide than does the evidence of animals that lived 
in the relatively unchanging water of the oceans. The 
nature of the evidence has already been indicated in 
various parts of this book. It includes palms, tree ferns, 
and a host of other plants which once grew in regions 
which are now much too cold to support them. With this 
must be placed the abundant reef-building corals and 
other warmth-loving marine creatures in latitudes now 
much too cold for them. Of a piece with this are the condi- 
tions of inter-glacial epochs in Europe, for example, 
when elephants and hippopotamuses, as well as many 
species of plants from low latitudes, were abundant. 
These conditions indicate not only that the climate was 
warmer than now, but that the contrast from season to 
season was much less. Indeed, Ejiowlton goes so far as 
to say that ** relative uniformity, mildness, and compara- 
tive equability of climate, accompanied by high hmnidity, 
have prevailed over the greater part of the earth, extend- 
ing to, or into, polar circles, during the greater part of 
geologic time — since, at least, the Middle Paleozoic. This 
is the regular, the ordinary, the normal condition. * * . . . 
**By many it is thought that one of the strongest argu- 
ments against a gradually cooling globe and a humid, 
non-zonally disposed climate in the ages before the Pleis- 
tocene is the discovery of evidences of glacial action 

2 F. H. Enowlton : Evolution of Geologic Glimatee ; Bull. Geol. Soe. Am., 
VoL 30, 1919, pp. 499-566. 


practically throughout the entire geologic column. 
Hardly less than a dozen of these are now known, ranging 
in age from Huronian to Eocene. It seems to be a very 
general assumption by those who hold this view that 
these evidences of glacial activities are to be classed as 
ice ageSy largely comparable in effect and extent to the 
Pleistocene refrigeration, but as a matter of fact only 
three are apparently of a magnitude to warrant such 
designation. These are the Huronian glaciation, that of 
the * Permo-Carbonif erous, ' and that of the Pleistocene. 
The others, so far as available data go, appear to be 
explainable as more or less local manifestations that had 
no widespread effect on, for instance, ocean tempera- 
tures, distribution of life, et cetera. They might well have 
been of the type of ordinary mountain glaciers, due en- 
tirely to local elevation and precipitation. ' * . . . * * If the 
sun had been the principal source of heat in pre-Pleisto- 
cene time, terrestrial temperatures would of necessity 
have been disposed in zones, whereas the whole trend of 
this paper has been the presentation of proof that these 
temperatures were distinctly non-zonal. Therefore it 
seems to follow that the sun — at least the present small- 
angle sun — could not have been the sole or even the prin- 
cipal source of heat that warmed the early oceans. ' ' 

Kiiowlton is so strongly impressed by the widespread 
fossil floras that usually occur in the middle parts of the 
geological periods, that as Schuchert' puts it, he neglects 
the evidence of other kinds. In the middle of the periods 
and eras the expansion of the warm oceans over the con- 
tinents was greatest, while the lands were small and 
hence had more or less insular climates of the oceanic 
type. At such times, the marine fauna agrees with the 

sChas. Schuchert: Beview of Knowlton's Evolution of Geological Cli- 
mates, in Am. Jour. Sci., 1921. 


flora in indicating a mild climate. Large colony-forming 
foraminifera, stony corals, shelled cephalopods, gastro- 
pods and thick-shelled bivalves, generally the cemented 
forms, were common in the Far North and even in the 
Arctic. This occurred in the Silurian, Devonian, Penn- 
sylvanian, and Jurassic periods, yet at other times, such 
as the Cretaceous and Eocene, such forms were very 
greatly reduced in variety in the northern regions or else 
wholly absent. These things, as Schuchert' says, can only 
mean that Ejiowlton is right when he states that '^ cli- 
matic zoning such as we have had since the beginning of 
the Pleistocene did not obtain in the geologic ages prior 
to the Pleistocene.'^ It does not mean, however, that 
there was a ** non-zonal arrangement and that the tem- 
perature of the oceans was everywhere the same and 
** without widespread effect on the distribution of life.*' 
Students of paleontology hold that as far back as we 
can go in the study of plants, there are evidences of sea- 
sons and of relatively cool climates in high latitudes. The 
cycads, for instance, are one of the types most often used 
as evidence of a warm climate. Yet Wieland,^ who has 
made a lifelong study of these plants, says that many of 
them ** might well grow in temperate to cool climates. 
Until far more is learned about them they should at least 
be held as valueless as indices of tropic climates." The 
inference is **that either they or their close relatives had 
the capacity to live in every clime. There is also a sus- 
picion that study of the associated ferns may compel re- 
vision of the long-accepted view of the universality of 
tropic climates throughout the Mesozoic." Nathorst is 
quoted by Wieland as saying, * * I think . . . that during 
the time when the Gingkophytes and Cycadophytes domi- 

^G. B. Wieland: Distribution and Belationships of the Cyeadeoids; Am. 
Jour. Bot, Vol. 7, 1920, pp. 125-145. 


natedy many of them must have adapted themselves for 
living in cold climates also. Of this I have not the least 

Another important line of evidence which Knowlton 
and others have cited as a proof of the non-zonal arrange- 
ment of climate in the past, is the vast red beds which are 
found in the Proterozoic, late Silurian, Devonian, Per- 
mian, and Triassic, and in some Tertiary formations. 
These are believed to resemble laterite, a red and highly 
oxidized soil which is found in great abundance in equa- 
torial regions. Knowlton does not atteitipt to show that 
the red beds present equatorial characteristics in other 
respects, but bases his conclusion on the statement that 
'^red beds are not being formed at the present time in 
any desert region. '^ This is certainly an error. As has 
already been said, in both the Transcaspian and TaMa 
Makan deserts, the color of the sand regularly changes 
from brown on the borders to pale red far out in the 
desert. Kuzzil Kum, or Bed Sand, is the native name. 
The sands in the center of the desert apparently were 
originally washed down from the same mountains as 
those on the borders, and time has turned them red. 
Since the same condition is reported from the Arabian 
Desert, it seems that redness is characteristic of some of 
the world's greatest deserts. Moreover, beds of salt and 
gypsum are regularly found in red beds, and they can 
scarcely originate except in deserts, or in shallow ahnost 
landlocked bays on the coasts of deserts, as appears to 
have happened in the Silurian where marine fossils are 
found interbedded with gypsum. 

Again, Ejiowlton says that red beds cannot indicate 
deserts because the plants found in them are not 
'* pinched or depauperate, nor do they indicate xero- 
phytic adaptations. Moreover, very considerable deposits 


of coal are found in red beds in many parts of the world, 
which implies the presence of swamps but little above 

Students of desert botany are likely to doubt the force 
of these considerations. As MacDougaP has shown, the 
variety of plants in deserts is greater than in moist 
regions. Not only do xerophytic desert species prevail, 
but halophytes are present in the salty areas, and hygro- 
phytes in the wet swampy areas, while ordinary meso- 
phytes prevail along the water courses and are washed 
down from the mountains. The ordinary plants, not the 
xerophytes, are the ones that are chiefly preserved since 
they occur in most abundance near streams where deposi- 
tion is taking place. So far as swamps are concerned, few 
are of larger size than those of Seistan in Persia, Lop 
Nor in Chinese Turkestan, and certain others in the midst 
of the Asiatic deserts. Streams flowing from the moun- 
tains into deserts are almost sure to form large swamps, 
such as those along the Tarim Biver in central Asia. 
Lake Chad in Africa is another example. In it, too, reeds 
are very numerous. 

Putting together the evidence on both sides in this dis- 
puted question, it appears that throughout most of geo- 
logical time there is some evidence of a zonal arrange- 
ment of climate. The evidence takes the form of traces of 
cool climates, of seasons, and of deserts. Nevertheless, 
there is also strong evidence that these conditions were 
in general less intense than at present and that times of 
relatively warm, moist climate without great seasonal 
extremes have prevailed very widely during periods 
much longer than those when a zonal arrangement as 

8D. T. MacDongal: Botanical Features of North American Deserts; 
Carnegie Instit. of Wash., No. 99, 1908. 


marked as that of today prevailed. As Schuchert* puts it : 
* * Today the variation on land between the tropics and the 
poles is roughly between 110** and — 60°F., in the oceans 
between 85^ and Sl^'F. In the geologic past the tempera- 
ture of the oceans for the greater parts of the periods 
probably was most often between 85° and 55°F,, while on 
land it may have varied between 90'' and 0°F. At rare 
intervals the extremes were undoubtedly as great as they 
are today. The conclusion is therefore that at all times 
the earth had temperature zones^ varying between the 
present-day intensity and times which were almost with- 
out such belts, and at these latter times the greater part 
of the earth had an almost uniformly mild climate, with- 
out winters. ' ' 

It is these mild climates which we must now attempt 
to explain. This leads us to inquire what would happen to 
the climate of the earth as a whole if the conditions which 
now prevail at times of few sunspots were to become 
intensified. That they could become greatly intensified 
seems highly probable, for there is good reason to think 
that aside from the sunspot cycle the sun's atmosphere 
is in a disturbed condition. The prominences which 
sometimes shoot out hundreds of thousands of miles 
seem to be good evidence of this. Suppose that the sun's 
atmosphere should become very quiet. This would appar- 
ently mean that cyclonic storms would be much less 
numerous and less severe than during the present times 
of sunspot minima. The storms would also apparently 
follow paths in middle latitudes somewhat as they do 
now when sunspots are fewest. The first effect of such a 
condition, if we can judge from what happens at present, 
would be a rise in the general temperature of the earth, 
because less heat would be carried aloft by storms. 

• Loe, cit. 


Today, as is shown in Earth and Sun, a difference of 
perhaps 10 per cent in the average storminess during 
periods of sunspot maxima and minima is correlated with 
a difference of S'^C. in the temperature at the earth's 
surface. This includes not only an actual lowering of 
0.6'' C. at times of sunspot maxima, but the overcoming 
of the effect of increased insolation at such times, an 
effect which Abbot calculates as about 2.5° C. If the 
storminess were to be reduced to one-half or one-quarter 
its present amount at sunspot minima, not only would the 
loss of heat by upward convection in storms be dimin- 
ished, but the area covered by clouds would diminish so 
that the sun would have more chance to warm the lower 
air. Hence the average rise of temperature might amount 
to as much at 5° or 10° C. 

Another effect of the decrease in storminess would be 
to make the so-called westerly winds, which are chiefly 
southwesterly in the northern hemisphere and north- 
westerly in tiie southern hemisphere, more strong and 
steady than at present. They would not continually suffer 
interruption by cyclonic winds from other directions, as 
is now the case, and would have a regularity like that 
of the trades. This conclusion is strongly reenforced in 
a paper by Clayton^ which came to hand after this chap- 
ter had been completed. From his studies of the solar 
constant and the temperature of the earth which are 
described in Earth and Sun, he reaches the following 
conclusion: **The results of these researches have led 
me to believe : 1. That if there were no variation in solar 
radiation the atmospherio motions would establish a 
stable system with exchanges of air between equator and 
pole and between ocean and land, in which the only varia- 

7 H. H. Clayton : Variation in Solar Badiation and the Weather ; Smiths. 
Miec ColL, Vol. 71, No. 3, Washington, 1920. 


tions would be daily and annual changes set in operation 
by the relative motions of the earth and sun. 2. The exist- 
ing abnormal changes, which we call weather, have their 
origins chiefly, if not entirely, in the variations of solar 
radiation. * * 

If cyclonic storms and ** weather^' were largely elimi- 
nated and if the planetary system of winds with its 
steady trades and southwesterlies became everywhere 
dominant, the regularity and volume of the poleward- 
flowing currents, such as the Gulf Stream and the 
Atlantic Drift in one ocean, and the Japanese Current in 
another, would be greatly increased. How important this 
is may be judged from the work of Helland-Hansen and 
Nansen.* These authors find that with the passage of each 
cyclonic storm there is a change in the temperature of 
the surface water of the Atlantic Ocean. Winds at right 
angles to the course of the Drift drive the water first in 
one direction and then in the other but do not advance it 
in its course. Winds with an easterly component, on the 
other hand, not only check the Drift but reverse it, driv- 
ing the warm water back toward the southwest and 
allowing cold water to well up in its stead. The driving 
force in the Atlantic Drift is merely the excess of the 
winds with a westerly component over those with an 
easterly component. 

Suppose that the numbers in Fig. 8 represent the 
strength of the winds in a certain part of the North 
Atlantic or North Pacific, that is, the total number of 
miles moved by the air per year. In quadrant A of the 
left-hand part all the winds move from a more or less 
southwesterly direction and produce a total movement 

SB. Helland-Hansen and F. Nansen: Temperature Variations in tlie 
North Atlantic Ocean and in the Atmosphere; Misc. Ck>Il., Smiths. Inst., Vol. 
70, No. 4, Washington, 1920. 








1 c 



yT 60 

Fig. 6. Effect of diminution of storms on 
movement of water. 

of the air amounting to thirty units per year. Those 
coming from points between north and west move twenty- 
five units ; those between north and east, twenty units ; 
and those between east and south, twenty-five units. 
Since the movement of the winds in quadrants B and 
D is the same, these winds have no effect in producing 
currents. They merely move the water back and forth, 
and thus give it time to lose whatever heat it has brought 
from more southerly latitudes. On the other hand, since 
the easterly winds in quadrant C do not wholly check the 
currents caused by the westerly winds of quadrant A, 
the effective force of the westerly winds amounts to ten, 
or the difference between a force of thirty in quadrant A 
and of twenty in quadrant C. Hence the water is moved 
forward toward the northeast, as shown by the thick 
part of arrow A. 

Now suppose that cyclonic storms should be greatly 
reduced in number so that in the zone of prevailing 
westerlies they were scarcely more numerous than tropi- 


cal hurricanes now are in the trade-wind belt. Then the 
more or less southwesterly winds in quadrant A' in the 
right-hand part of Fig. 8 would not only become more 
frequent but would be stronger than at present. The 
total movement from that quarter might rise to sixty 
units, as indicated in the figure. In quadrants B' and D^ 
the movement would fall to fifteen and in quadrant C to 
ten. B' and D' would balance one another as before. The 
movement in A', however, would exceed that in C by fifty 
instead of ten. In other words, the current-making force 
would become five times as great as now. The actual 
effect would be increased still more, for the winds from 
the southwest would be stronger as well as steadier if 
there were no storms. A strong wind which causes white- 
caps has much more power to drive the water forward 
than a weaker wind which does not cause whitecaps. In a 
wave without a whitecap the water returns to practically 
the original point after completing a circle beneath the 
surface. In a wave with a whitecap, however, the cap 
moves forward. Any increase in velocity beyond the rate 
at which whitecaps are formed has a great influence upon 
the amount of water which is blown forward. Several 
times as much water is drifted forward by a persistent 
wind of twenty miles an hour as by a ten-mile wind.* 

In this connection a suggestion which is elaborated in 
Chapter XIII may be mentioned. At present the salinity 
of the oceans checks the general deep-sea circulation and 
thereby increases the contrasts from zone to zone. In the 
past, however, the ocean must have been fresher than 
now. Hence the circulation was presumably less impeded, 
and the transfer of heat from low latitudes to high was 

• The dimatie significance of ocean currents is well discussed in OroU'e 
Climate and Time^ 1875, and his Climate and Cosmogony, 1889. 


Consider now the magnitude of the probable efEect of 
a diminution in storms. Today off the coast of Norway 
in latitude 65^N. and longitude 10°E., the mean tempera- 
ture in January is 2°C. and in July 12°C. This represents 
a plus anomaly of about 22° in January and 2° in July; 
that isy the Norwegian coast is warmer than the normal 
for its latitude by these amounts. Suppose that in some 
past time the present distribution of lands and seas pre- 
vailed, but Norway was a lowland where extensive de- 
posits could accumulate in great flood plains. Suppose, 
also, that the sun's atmosphere was so inactive that few 
cyclonic storms occurred, steady winds from the west- 
southwest prevailed, and strong, uninterrupted ocean 
currents brought from the Caribbean Sea and Gulf of 
Mexico much greater supplies of warm water than at 
present. The Norwegian winters would then be warmer 
than now not only because of the general increase in tem- 
perature which the earth regularly experiences at sun- 
spot minima, but because the currents would accentuate 
this condition. Li summer similar conditions would pre- 
vail except that the warming effect of the winds and 
currents would presumably be less than in winter, but 
this might be more than balanced by the increased heat 
of the 8^ during the long smmner days, for storms and 
clouds would be rare. 

If such conditions raised the winter temperature only 
8®C. and the summer temperature 4°C., the climate would 
be as warm as that of the northern island of New Zealand 
(latitude 35M3°S.). The flora of that part of New Zea- 
land is subtropical and includes not only pines and 
beeches, but palms and tree ferns. A climate scarcely 
warmer than that of New Zealand would foster a flora 
like that which existed in far northern latitudes during 
some of the milder geological periods. If, however, the 


general temperature of the earth's surface were raised 
5** because of the scarcity of storms, if the currents were 
strong enough so that they increased the present anomaly 
by 50 per cent, and if more persistent sunshine in summer 
raised the temperature at that season about 4°0., the 
January temperature would be 18°C. and the July tem- 
perature 22 ""C. These figures perhaps make summer and 
winter more nearly alike than was ever really the case in 
such latitudes. Nevertheless, they show that a diminution 
of storms and a consequent strengthening and steadying 
of the southwesterlies might easily raise the temperature 
of the Norwegian coast so high that corals could flourish 
within the Arctic Circle. 

Another factor would cooperate in producing mild 
temperatures in high latitudes during the winter, namely, 
the fogs which would presumably accumulate. It is well 
known that when saturated air from a warm ocean is 
blown over the lands in winter, as happens so often in the 
British Islands and around the North Sea, fog is formed. 
The effect of such a fog is indeed to shut out the sun's 
radiation, but in high latitudes during the winter when 
the sun is low, this is of little importance. Another effect 
is to retain the heat of the earth itself. When a constant 
supply of warm water is being brought from low lati- 
tudes this blanketing of the heat by the fog becomes of 
great importance. In the past, whenever cyclonic storms 
were weak and westerly winds were correspondingly 
strong, winter fogs in high latitudes must have been much 
more widespread and persistent than now. 

The bearing of fogs on vegetation is another interest- 
ing point. If a region in high latitudes is constantly pro- 
tected by fog in winter, it can support types of vegetation 
characteristic of fairly low latitudes, for plants are 
oftener killed by dry cold than by moist cold. Indeed, 


excessive evaporation from the plant induced by dry 
cold when the evaporated water cannot be rapidly re- 
placed by the movement of sap is a chief reason why 
large plants are winterkilled. The growing of trans- 
planted palms on the coast of sonthwestem Ireland, in 
spite of its location in latitude SO'^N., is possible only be- 
cause of the great fogginess in winter due to the marine 
climate. The fogs prevent the escape of heat and ward off 
killing frosts. The tree ferns in latitude 46° S. in New 
Zealand, already referred to, are often similarly pro- 
tected in winter. Therefore, the relative frequency of fogs 
in high latitudes when storms were at a minimum would 
apparently tend not merely to produce mild winters but 
to promote tropical vegetation. 

The strong steady trades and southwesterlies which 
would prevail at times of slight solar activity, according 
to our hypothesis, would have a pronounced effect on the 
water of the deep seas as well as upon that of the surface. 
In the first place, the deep-sea circulation would be has- 
tened. For convenience let us speak of the northern hemi- 
sphere. In the past, whenever the southwesterly winds 
were steadier than now, as was probably the case when 
cyclonic storms were relatively rare, more surface water 
than at present was presumably driven from low latitudes 
and carried to high latitudes. This, of course, means that 
a greater volume of water had to flow back toward the 
equator in the lower parts of the ocean, or else as a cool 
surface current. The steady southwesterly winds, how- 
ever, would interfere with south-flowing surface currents, 
thus compelling the polar waters to find their way 
equatorward beneath the surface. In low latitudes the 
polar waters would rise and their tendency would be to 
lower the temperature. Hence steadier westerlies would 
make for lessened latitudinal contrasts in climate not 


only by driving more warm water poleward but by caus- 
ing more polar water to reach low latitudes. 

At this point a second important consideration must be 
faced. Not only would the deep-sea circulation be has- 
tened, but the ocean depths might be warmed. The deep 
parts of the ocean are today cold because they receive 
their water from high latitudes where it sinks because of 
low temperature. Suppose, however, that a diminution in 
storminess combined with other conditions should permit 
corals to grow in latitude 70°N. The ocean temperature 
would then have to average scarcely lower than 20**C. 
and even in the coldest month the water could scarcely 
fall below about 15^0. Under such conditions, if the polar 
ocean were freely connected with the rest of the oceans, 
no part of it would probably have a temperature much 
below 10° C, for there would be no such thing as ice caps 
and snowfields to reflect the scanty sunlight and radiate 
into space what little heat there was. On the contrary, 
during the winter an almost constant state of dense f og- 
giness would prevail. So great would be the blanketing 
effect of this that a minimum monthly temperature of 
10° C. for the coldest part of the ocean may perhaps be 
too low for a time when corals thrived in latitude 70°. 

The temperature of the ocean depths cannot perma- 
nently remain lower than that of the coldest parts of the 
surface. Temporarily this might indeed happen when a 
solar change first reduced the storminess and strength- 
ened the westerlies and the surface currents. Gradually, 
however, the persistent deep-sea circulation would bring 
up the colder water in low latitudes and carry downward 
the water of medium temperature at the coldest part of 
the surface. Thus in time the whole body of the ocean 
would become warm. The heat which at present is carried 
away from the earth's surface in storms would slowly 


accumulate in the oceans. As the process went on, all 
parts of the ocean's surface would become warmer, for 
equatorial latitudes would be less aad less cooled by cold 
water from below, while the water blown from low lati- 
tudes to high would be correspondingly warmer. The 
warming of the ocean would come to an end only with 
the attainment of a state of equilibrium in which the loss 
of heat by radiation and evaporation from the ocean's 
surface equaled the loss which xmder other circumstances 
would arise from the rise of warm air in cyclonic storms. 
When once the oceans were warmed, they would form an 
extremely strong conservative force tending to preserve 
an equable climate in all latitudes and at all seasons. 
According to the solar cyclonic hypothesis such condi- 
tions ought to have prevailed throughout most of geo- 
logical time. Only after a strong and prolonged solar 
disturbance with its consequent storminess would condi- 
tions like those of today be expected. 

In this connection another possibility may be men- 
tioned. It is commonly assumed that the earth's axis is 
held steadily in one direction by the fact that the rotating 
earth is a great gyroscope. Having been tilted to a cer- 
tain position, perhaps by some extraneous force, the axis 
is supposed to maintain that position until some other 
force intervenes. Cordeiro," however, maintains that this 
is true only of an absolutely rigid gyroscope. He believes 
that it is mathematically demonstrable that if an elastic 
gyroscope be gradually tilted by some extraneous force, 
and if that force then ceases to act, the gyroscope as a 
whole will oscillate back and forth. The earth appears to 
be slightly elastic. Cordeiro therefore applies his for- 
mulae to it, on the following assumptions: (1) That the 
original position of the axis was nearly vertical to the 

10 p. J. B. Cordeiro: The Gyroscope, 1913. 


plane of the ecliptic in which the earth revolves around 
the sun ; (2) that at certain times the inclination has been 
even greater than now; and (3) that the position of the 
axis with reference to the earth has not changed to any 
great extent, that is, the earth *s poles have remained 
essentially stationary with reference to the earth, al- 
though the whole earth has been gyroscopically tilted 
back and forth repeatedly. 

With a vertical axis tiie daylight and darkness in all 
parts of the earth would be of equal duration, being 
always twelve hours. There would be no seasons, and the 
climate would approach the average condition now ex- 
perienced at the two equinoxes. On the whole the climate 
of high latitudes would give the impression of being 
milder than now, for there would be less opportimity for 
the accumulation of snow and ice with their strong cool- 
ing effect On the other hand, if the axis were tilted more 
than now, the winter nights would be longer and the 
winters more severe than at present, and there would be 
a tendency toward glaciation. Thus Oordeiro accounts 
for alternating mild and glacial epochs. The entire swing 
from the vertical position to the maximum indination 
and back to the vertical may last millions of years de- 
pending on the earth's degree of elasticity. The swing 
beyond the vertical position in the other direction would 
be equally prolonged. Since the axis is now supposed to 
be much nearer its maximum than its minimum degree of 
tilting, the duration of epochs having a climate more 
severe than that of the present would be relatively short, 
while the mild epochs would be long. 

Cordeiro's hypothesis has been almost completely 
ignored. One reason is that his treatment of geological 
facts, and especially his method of riding rough-shod 
over widely accepted conclusions, has not commended his 


work to geologists. Therefore they have not deemed it 
worth while to urge mathematicians to test the assump- 
tions and methods by which he reached his results. It is 
perhaps mifair to test Cordeiro by geology, for he lays 
no claim to being a geologist In mathematics he labors 
under the disadvantage of having worked outside the 
usual professional channels, so that his work does not 
seem to have been subjected to sufficiently critical 

Without expressing any opinion as to the value of 
Cordeiro *s results we feel that the subject of the earth *s 
gyroscopic motion and of a possible secular change in 
the direction of the axis deserves investigation for two 
chief reasons. In the first place, evidences of seasonal 
changes and of seasonal uniformity seem to occur more 
or less alternately in the geological record. Second, the 
remarkable discoveries of Gamer and Allard^^ show that 
the duration of daylight has a pronounced effect upon 
the reproduction of plants. We have referred repeatedly 
to the tree ferns, corals, and other forms of life which 
now live in relatively low latitudes and which cannot 
endure strong seasonal contrasts, but which once lived 
far to the north. On the other hand, Sayles," for example, 
finds that microscopical examination of the banding of 
ancient shales and slates indicates distinct seasonal band- 
ing like that of recent Pleistocene clays or of the Squan- 
tum slate formed during or near the Permian glacial 
period. Such seasonal banding is found in rocks of vari- 
ous ages: (a) Huronian, in cobalt shales previously 
reported by Coleman ; (b) late Proterozoic or early Cam- 

XI W. W. Qarner and H. A. Allard: Flowering and Fmition of Plants 
as Ck>ntrolled by Length of Day; Yearbook Dept. Agri., 1920, pp. 377-400. 

i2Beport of Oonunittee on Sedimentation, National Research Council, 
AprU, 1922. 


brian, in Hiwassee slate ; (c) lower Cambrian^ in Geor- 
gian slates of Vermont; (d) lower Ordovician, in Geoxgia 
(Bockmart slate), Tennessee (Athens shale), Vermont 
(slates), and Quebec (Beekmantown formation) ; and (e) 
Permian in Massachusetts (Squantum slate). How far 
the periods during which such evidence of seasons was 
recorded really alternated with mild periods, when tropi- 
cal species lived in high latitudes and the contrast of 
seasons was almost or wholly lacking, we have as yet no 
means of knowing. If periods characterized by marked 
seasonal changes should be found to have alternated with 
those when the seasons were of little importance, the fact 
would be of great geological significance. 

The discoveries of Gamer and Allard as to the effect 
of light on reproduction began with a peculiar tobacco 
plant which appeared in some experiments at Washing- 
ton. The plant grew to unusual size, and seemed to 
promise a valuable new variety. It formed no seeds, how- 
ever, before the approach of cold weather. It was there- 
fore removed to a greenhouse where it flowered and 
produced seed. In succeeding years the flowering was 
likewise delayed till early winter, but finally it was dis- 
covered that if small plants were started in the green- 
house in the early fall they flowered at the same time as 
the large ones. Experiments soon demonstrated that the 
time of flowering depends largely upon the length of the 
daily period when the plants are exposed to light. The 
same is true of many other plants, and there is great 
variety in the conditions which lead to flowering. Some 
plants, such as witch hazel, appear to be stimulated to 
bloom by very short days, while others, such as evening 
primrose, appear to require relatively long days. So 
sensitive are plants in this respect that Gamer and 
Allard, by changing the length of the period of light, have 


caused a flowerbud in its early stages not only to stop 
developing but to return once more to a vegetative shoot. 

Common iris, which flowers in May and June, will not blossom 
under ordinary conditions when grown m the greenhouse in 
winter, even under the same temperature conditions that prevail 
in early summer. Again, one variety of soy beans will regularly 
begin to flower in June of each year, a second variety in July, 
and a third in August, when all are planted on the same date. 
There are no temperature differences during the summer months 
which could explain these differences in time of flowering; and, 
since ''internal causes" alone cannot be accepted as furnishing 
a satisfactory explanation, some external factor other than tem- 
perature must be responsible. 

The ordinary varieties of cosmos regularly flower in the fall 
in northern latitudes if they are planted in the spring or summer. 
If grown in a warm greenhouse during the winter months the 
plants also flower readily, so that the cooler weather of fall is 
not a necessary condition. If successive plantings of cosmos are 
made in the greenhouse during the late winter and early spring 
months, maintaining a uniform temperature throughout, the 
plantings made after a certain date will fail to blossom promptly, 
but, on the contrary, will continue to grow till the following fall, 
thus flowering at the usual season for this species. This curious 
reversal of behavior with advance of the season cannot be attrib- 
uted to change in temperature. Some other factor is responsible 
for the failure of cosmos to blossom during the summer months. 
In this respect the behavior of cosmos is just the opposite of that 
observed in iris. 

Certain varieties of soy beans change their behavior in a 
peculiar manner with advance of the summer season. The variety 
known as Biloxi, for example, when planted early in the spring 
in the latitude of Washington, D. C, continues to grow through- 
out the summer, flowering in September. The plants maintain 
growth without flowering for fifteen to eighteen weeks, attaining 
a height of five feet or more. As the dates of successive plantings 
are moved forward through the months of June and July, how- 


ever, there is a marked tendency for the plants to cut short the 
period of growth which precedes flowering. This means^ of course, 
that there is a tendency to flower at approximately the same time 
of year regardless of the date of planting. As a necessary con- 
sequence, the size of the plants at the time of flowering is reduced 
in proportion to the delay in planting. 

The bearing of this on geological problems lies in a 
query which it raises as to the ability of a genus or family 
of plants to adapt itself to days of very different length 
from those to which it is wonted. Could tree ferns, gink- 
gos, cycads, and other plants whose usual range of loca- 
tion never subjects them to daylight for more than 
perhaps fourteen hours or less than ten, thrive and re- 
produce themselves if subjected to periods of daylight 
ranging all the way from nothing up to about twenty- 
four hours! No answer to this is yet possible, but the 
question raises most interesting opportunities of in- 
vestigation. If Cordeiro is right as to the earth's elastic 
gyroscopic motion, there may have been certain periods 
when a vertical or almost vertical axis permitted the 
days to be of almost equal length at all seasons in all 
latitudes. If such an absence of seasons occurred when 
the lands were low, when the oceans were extensive and 
widely open toward the poles, and when storms were 
relatively inactive, the result might be great mildness of 
climate such as appears sometimes to have prevailed in 
the middle of geological eras. Suppose on the other hand 
that the axis should be tilted more than now, and that 
the lands should be widely emergent and the storm belt 
highly active in low latitudes, perhaps because of the 
activity of the sun. The conditions might be favorable for 
glaciation at latitudes as low as those where the Permo- 
Carboniferous ice sheets appear to have centered. The 
possibilities thus suggested by Cordeiro 's hypothesis are 


80 interesting that the gyroscopic motion of the earth 
onght to be investigated more thoroughly. Even if no 
such gyroscopic motion takes place, however, the other 
causes of mild climate discussed in this chapter may 
be enough to explain all the observed phenomena. 

Many important biological consequences might be 
drawn from this study of mild geological climates, but 
this book is not the place for them. In the first chapter 
we saw that one of the most remarkable features of the 
climate of the earth is its wonderful uniformity through 
hundreds of millions of years. As we come down through 
the vista of years the mild geological periods appear to 
represent a return as nearly as possible to this standard 
condition of mdformity. Certakt changes of the earth 
itself, as we shall see in the next chapter, may in the long 
run tend slightly to change the exact conditions of this 
climatic standard, as we might perhaps call it. Yet they 
act so slowly that their effect during hundreds of millions 
of years is still open to question. At most they seem 
merely to have produced a slight increase in diversity 
from season to season and from zone to zone. The normal 
climate appears still to be of a milder type than that 
which happens to prevail at present. Some solar condi- 
tion, whose possible nature will be discussed later, seems 
even now to cause the number of cyclonic storms to be 
greater than normal. Hence the earth's climate still 
shows something of the great diversity of seasons and 
of zones which is so marked a characteristic of glacial 



THE major portion of this book has been concerned 
with the explanation of the more abmpt and ex- 
treme changes of climate. This chapter and the 
next consider two other sorts of climatic changes, the 
slight secular progression during the hundreds of mil- 
lions of years of recorded earth history, and especially 
the long slow geologic oscillations of millions or tens of 
millions of years. It is generally agreed among geologists 
that the progressive change has tended toward greater 
extremes of climate ; that is, greater seasonal contrasts, 
and greater contrasts from place to place and from zone 
to zone.^ The slow cyclic changes have been those that 
favored widespread glaciation at one extreme near the 
ends of geologic periods and eras, and mild temperatures 
even in subpolar regions at the other extreme during the 
medial portions of the periods. 

As has been pointed out in an earlier chapter, it has 
often been assumed that all climatic changes are due to 
terrestrial causes. We have seen, however, that there is 
strong evidence that solar variations play a large part in 
modifying the earth 's climate. We have also seen that no 
known terrestrial agency appears to be able to produce 
the abrupt changes noted in recent years, the longer 

iChas. Schuehert: The Earth's Changing Surface and Climate daring 
Geologic Time; in Lull: The Evolution of the Earth and Its Inhabitants, 
1918, p. 55. 


cycles of historical times, or geological changes of the 
shorter type, such as glaciation. Nevertheless, terrestrial 
changes doubtless have assisted in producing both the 
progressive change and the slow cyclic changes recorded 
in the rocks, and it is the purpose of this chapter and the 
two that follow to consider what terrestrial changes have 
taken place and the probable effect of such changes. 

The terrestrial changes that have a climatic signifi- 
cance are numerous. Some, such as variations in the 
amount of volcanic dust in the higher air, have been con- 
sidered in an earlier chapter. Others are too imperfectly 
known to warrant discussion, and in addition there are 
presumably others which are entirely unknown. Doubt- 
less some of these little known or unknown changes have 
been of importance in modifying climate. For example, 
the climatic influence of vegetation, animals, and man 
may be appreciable. Here, however, we shall confine our- 
selves to purely physical causes, which will be treated in 
the following order : First, those concerned with the solid 
parts of the earth, namely: (I) amount of land; (II) dis- 
tribution of land; (in) height of land; (IV) lava flows; 
and (V) internal heat. Second, those which arise from 
the salinity of oceans, and third, those depending on the 
composition and amount of atmosphere. 

The terrestrial change which appears indirectly to 
have caused the greatest change in climate is the con- 
traction of the earth. The problem of contraction is 
highly complex and is as yet only imperfectly understood. 
Since only its results and not its processes influence cli- 
mate, the following section as far as page 196 is not 
necessary to the general reader. It is inserted in order to 
explain why we assume that there have been oscillations 
between certain types of distribution of the lands. 

The extent of the earth ^s contraction may be judged 


from the shrinkage indicated by the shortening of the 
rock formations in folded mountains such as the Alps, 
JuraSy Appalachians, and Caucasus. Gteologists are con- 
tinually discovering new evidence of thrust faults of 
great magnitude where masses of rock are thrust bodily 
over other rocks, sometimes for many miles. Therefore, 
the estimates of the amount of shrinkage based on the 
measurements of folds and faults need constant revision 
upward. Nevertheless, they have already reached a con- 
siderable figure. For example, in 1919, Professor ,A. Heim 
estimated the shortening of the meridian passing through 
the modem Alps and the ancient Hercynian and Cale- 
donian mountains as fully a thousand miles in Europe, 
and over five hundred miles for the rest of this meridian.* 
This is a radial shortening of about 250 miles. Possibly 
the shrinkage has been even greater than this. Chamber- 
lin' has compared the density of the earth, moon, Mars, 
and Venus with one another, and found it probable that 
the radial shrinkage of the earth may be as much as 
570 miles. This result is not so different from Heim's as 
appears at first sight, for Heim made no allowance for 
unrecognized thrust faults and for the contraction inci- 
dent to metamorphism. Moreover, Heim did not include 
shrinkage during the first half of geological time before 
the above-mentioned mountain systems were upheaved. 
According to a well-established law of physics, con- 
traction of a rotating body results in more rapid rotation 
and greater centrifugal force. These conditions must in- 
crease the earth's equatorial bulge and thereby cause 
changes in the distribution of land and water. Opposed 
to the rearrangement of the land due to increased rota- 

i Quoted by J. Cornet : Cours de G^ologie, 1920, p. 330. 
ST. C. Ohamberlin: The Order of Magnitude of the Shrinkage of the 
Earth; Jour. Geol., Vol. 28, 1920, pp. 1-17, 126-157. 


tion caused by contraction, there has presumably been 
another rearrangement due to tidal retardation of the 
earth's rotation and a consequent lessening of the equa- 
torial bulge. G. H. Darwin long ago deduced a relatively 
large retardation due to lunar tides. A few years ago 
W. D. MacMillaUy on other assumptions, deduced only a 
negligible retardation. Still more recently Taylor* has 
studied the tides of the Irish Sea, and his work has led 
Jeffreys" and Brown* to conclude that there has been con- 
siderable retardation, perhaps enough, according to 
Brown, to equal the acceleration due to the earth's con- 
traction. From a prolonged and exhaustive study of the 
motions of the moon Brown concludes that tidal friction 
or some other cause is now lengthening the day at the rate 
of one second per thousand years^ or an hour in almost 
four million years if the present rate continues. He makes 
it dear that the retardation due to tides would not corre- 
spond in point of time with the acceleration due to con- 
traction. The retardation would occur slowly, and would 
take place chiefly during the long quiet periods of geo- 
logic history, whUe the acceleration would occur rapidly 
at times of diastrophic deformation. As a consequence, 
the equatorial bulge would alternately be reduced at a 
slow rate, and then somewhat suddenly augmented. 

The less rigid any part of the earth is, the more quickly 
it responds to the forces which lead to bulging or which 
tend to lessen the bulge. Since water is more fluid than 
land, the contraction of the earth and the tidal retarda- 
tion presumably tend alternately to increase and decrease 
the amount of water near the equator more than the 

«G. I. Taylor: PhiloBophical Transactions, A. 220, 1919, pp. 1-33; 
Monthlj Notiees Bojal Astron. Soc, Jan., 1920, Vol. 80, p. 308. 

fi J. Jeffreys : Monthlj Notices. Boyal Astron. Soc, Jan., 1920, Vol. 80, 
p. 309. 

9 £. W. Brown : personal communication. 



amount of land. Thus, throughout geological history we 
should look for cyclic changes in the relative area of the 
lands within the tropics and similar changes of opposite 
phase in higher latitudes. The extent of the change would 
depend upon (a) the amount of alteration in the speed 
of rotation, and (b) the extent of low land in low lati- 
tudes and of shallow sea in high latitudes. According to 
Slichter's tables, if the earth should rotate in twenty- 
three hours instead of twenty-four, the great Amazon 
lowland would be submerged by the inflow of oceanic 
water, while wide areas in Hudson Bay, the North Sea, 
and other northern regions, would become land because 
the ocean water would flow away from them.' 

Following the prompt equatorward movement of water 
which would occur as the speed of rotation increased, 
there must also be a gradual movement or creepage of the 
solid rocks toward the equator, that is, a bulging of the 
ocean floor and of the lands in low latitudes, with a con- 
sequent emergence of the lands there and a relative 
rise of sea level in higher latitudes. Tidal retardation 
would have a similar effect. Suess" has described wide- 
spread elevated strand lines in the tropics which he in- 
terprets as indicating a relatively sudden change in sea 
level, though he does not suggest a cause of the change. 
However, in speaking of recent geological times, Suess 
reports that a movement more recent than the old 
strands ^^was an accumulation of water toward the 
equator, a diminution toward the poles, and (it appears) 
as though this last movement were only one of the many 
oscillations which succeed each other with the same tend- 
ency, i.e., with a positive excess at the equator, a nega- 

• 7 G. S. Blichter: The Rotational Period of a Heterogeneous Spheroid; in 
Contributions to the Fundamental Problems of Geology, by T. C. Gfaimt- 
berlin, et al,, Carnegie Inst, of Wash., No. 107, 1909. 

8 E. Suess: The Face of the Earth, Vol. II, p. 553, 1901. 


tive excess at the poles/' (Vol. II, p. 551.) This creepage 
of the rocks equatorward seemingly might favor the 
growth of mountains in tropical and subtropical regions, 
because it is highly improbable that the increase in the 
bulge would go on in all longitudes with perfect uni- 
formity. Where it went on most rapidly mountains would 
arise. That such irregularity of movement has actually 
occurred is suggested not only by the fact that many 
Cenozoic and older mountain ranges extend east and 
west, but by the further fact that these include some of 
our greatest ranges, many of which are in fairly low lati- 
tudes. The Himalayas, the Javanese ranges, and the half- 
submerged Caribbean chains are examples. Such moun- 
tains suggest a thrust in a north and south direction 
which is just what would happen if the solid mass of the 
earth were creeping j&rst equatorward and then poleward. 

A fact which is in accord with the idea of a periodic 
increase in the oceans in low latitudes because of renewed 
bulging at the equator is the exposure in moderately 
high latitudes of the greatest extent of ancient rocks. 
This seems to mean that in low latitudes the frequent 
deepening of the oceans has caused the old rocks to be 
largely covered by sediments, while the old lands in 
higher latitudes have been left more fully exposed to 

Another suggestion of such periodic equatorward move- 
ments of the ocean water is found in the reported contrast 
between the relative stability with which the northern part 
of North America has remained slightly above sea level 
except at times of widespread submergence, while the 
southern parts have suffered repeated submergence al- 
ternating with great emergence.* Furthermore, although 

• Chas. Sehnehert: The Earth's Changing Surface and Climate; in Lull: 
The Evolution of the Earth and Its Inhabitants, 1918, p. 78. 


the northern part of North America has been generally 
exposed to erosion since the Proterozoic, it has supplied 
much less sediment than have the more southern land 
areas." This apparently means that much of Canada has 
stood relatively low, while repeated and profound uplift 
alternating with depression has occurred in subtropical 
latitudes, apparently in adjustment to changes in the 
earth's speed of rotation. The uplifts generally followed 
the times of submergence due to equatorward movement 
of the water, though the buckling of the crust which ac- 
companies shrinkage doubtless caused some of the sub- 
mergence. The evidence that northern North America 
stood relatively low throughout much of geological time 
depends not only on the fact that little sediment came to 
the south from the north, but also on the fact that at 
times of especially widespread epicontinental seas, the 
submergence was initiated at the north." This is espe- 
cially true for Ordovician, Silurian, Devonian, and Juras- 
sic times in North America. General submergence of this 
kind is supposed to be due chiefly to the overflowing of 
the ocean when its level is slowly raised by the deposition 
of sediment derived from the erosion of what once were 
continental highlands but later are peneplains. The fact 
that such submergence began in high latitudes, however, 
seems to need a further explanation. The bulging of the 
rock sphere at the equator and the consequent displace- 
ment of some of the water in low latitudes would furnish 
such an explanation, as would also a decrease in the speed 
of rotation induced by tidal retardation, if that retarda- 
tion were great enough and rapid, enough to be geologi- 
cally effective. 

10 J. Barrell: Bhythms and the Measurement of Geologic Time; BnlL 
Geol. Soc. Am., Vol. 28, 1917, p. 838. 

11 Chas. Schuchert : loc, cit., p. 78. 


The climatic effects of the earth's contraction, which 
we shall shortly discuss, are greatly complicated by the 
fact that contraction has taken place irregularly. Such 
irregularity has occurred in spite of the fact that the 
processes which cause contraction have probably gone 
on quite steadily throughout geological history. These 
processes include the chemical reorganization of the min- 
erals of the crust, a process which is illustrated by the 
metamorphism of sedimentary rocks into crystalline 
forms. The escape of gases through volcanic action or 
otherwise has been another important process. 

Although the processes which cause contraction prob- 
ably go on steadily, their effect, as Chamberlin" and 
others have pointed out, is probably delayed by inertia. 
Thus the settling of the crust or its movement on a large 
scale is delayed. Perhaps the delay continues until the 
stresses become so great that of themselves they over- 
come the inertia, or possibly some outside agency, whose 
nature we shall consider later, reenf orces the stresses and 
gives the slight impulse which is enough to release them 
and allow the earth's crust to settle into a new state of 
equilibrium. When contraction proceeds actively, the 
ocean segments, being largest and heaviest^ are likely to 
settle most, resulting in a deepening of the oceans and an 
emergence of the lands. Following each considerable con- 
traction there would be an increase in the speed of rota- 
tion. The repeated contractions with consequent growth 
of the equatorial bulge would alternate with long quiet 
periods during which tidal retardation would again de- 
crease the speed of rotation and hence lessen the bulge. 
The result would be repeated changes of distribution of 
land and water, with consequent changes in climate. 

1ST. 0. Ghamberlin: DiastTophism, the Ultimate Basis of Correlation; 
Jour. Geol., Vol. 16, 1909; Chas. Schnehert: loo. cit. 


L We shall now consider the climatic e£fect of the 
repeated changes in the relative amounts of land and 
water which appear to have resulted from the earth's 
contraction and from changes in its speed of rotation. 
During many geologic epochs a larger portion of the 
earth was covered with water than at present For ex- 
ample, during at least twelve out of about twenty epochs. 
North America has suffered extensive inundations^^' and 
in general the extensive submergence of Europe, the 
other area well known geologically, has coincided with 
that of North America. At other times, the ocean has 
been less extensive than now, as for example during the 
recent glacial period, and probably during several of 
the glacial periods of earlier date. Each of the numerous 
changes in the relative extent of the lands must have 
resulted in a modification of climate.^^ This modification 
would occur chiefly because water becomes warm far 
more slowly than land, and cools off far more slowly. 

An increase in the lands would cause changes in several 
climatic conditions, (a) The range of temperature be- 
tween day and night and between summer and winter 
would increase, for lands become warmer by day and in 
summer than do oceans, and cooler at night and in 
winter. The higher summer temperature when the lands 
are widespread is due chiefly to the fact that the land, if 
not snow-covered, absorbs more of the sun's radiant 
energy than does the ocean, for its reflecting power is 
low. The lower winter temperature when lands are wide- 
spread occurs not only because they cool off rapidly but 

"Pirsson-Schuchert: Textbook of Geology, 1915, Vol. n, p. 982; Chaa. 
Schuchert: Pideogeography of North America; BulL Geol. Soc. Anu, VoL 
20, pp. 427-606; reference on p. 499. 

14 The general subject of the climatic significance of continentality is 
discussed by G. E. P. Brooks: Gontinentality and Temperature; Quarts 
Jour. Bojal MeteoroL Soc, April, 1917, and Get, 1918. 


because the reduced oceans cannot give them so much 
heat. Moreover, the larger the land, the more generally 
do the winds blow outward from it in winter and thus 
prevent the ocean heat from being carried inland. So 
long as the ocean is not frozen in high latitudes, it is 
generally the chief source of heat in winter, for the nights 
are several months long near the poles, and even when 
the sun does shine its angle is so low that reflection from 
the snow is very great. Furthermore, although on the 
average there is more reflection from water than from 
land, the opposite is true in high latitudes in winter 
when the land is snow-covered while the ocean is rela- 
tively dark and is roughened by the waves. Another 
factor in causing large lands to have extremely low tem- 
perature in winter is the fact that in proportion to their 
size they are less protected by fog and cloud than are 
smaller areas. The belt of cloud and fog which is usually 
formed when the wind blows from the ocean to the rela- 
tively cold land is restricted to the coastal zone. Thus the 
larger the land, the smaller the fraction in which loss of 
heat by radiation is reduced by clouds and fogs. Hence 
an increase in the land area is accompanied by an in- 
crease in the contrasts in temperature between land and 

(b) The contrasts in temperature thus produced must 
cause similar contrasts in atmospheric pressure, and 
hence stronger barometric gradients, (c) The strong 
gradients would mean strong winds, flowing from land 
to sea or from sea to land, (d) Local convection would 
also be strengthened in harmony with the expansion of 
the lands, for the more rapid heating of land than of 
water favors active convection. 

(e) As the extent of the ocean diminished, there would 
normally be a decrease in the amount of water vapor for 


three reasons: (1) Evaporation from the ocean is the 
great source of water vapor. Other conditions being 
equaly the smaller the ocean becomes, the less the evapo- 
ration. (2) The amount of water vapor in the air dimin- 
ishes as convection increases, since upward convection 
is a chief method by which condensation and precipita- 
tion are produced, and water vapor removed from the 
atmosphere. (3) Nocturnal cooling sufficient to produce 
dew and frost is very much more common upon land than 
upon the ocean. The formation of dew and frost dimin- 
ishes the amount of water vapor at least temporarily, 
(f) Any diminution in water vapor produced in these 
ways, or otherwise, is significant because water vapor is 
the most essential part of the atmosphere so far as regu- 
lation of temperature is concerned. It tends to keep the 
days from becoming hot or the nights cold. Therefore 
any decrease in water vapor would increase the diurnal 
and seasonal range of temperature, making the climate 
more extreme and severe. Thus a periodic increase in the 
area of the continents would clearly make for periodic 
increased climatic contrasts, with great extremes, a type 
of climatic change which has recurred again and again. 
Indeed, each great glaciation accompanied or followed 
extensive emergence of the lands." 

Whether or not there has been a progressive increase 
from era to era in the area of the lands is uncertain. 
Good authorities disagree widely. There is no doubt, 
however, that at present the lands are more extensive 
than at most times in the past, though smaller, perhaps, 
than at certain periods. The wide expanse of lands helps 
explain the prominence of seasons at present as com- 
pared with the past. 

iBChas. Schuchert: Climates of Geologic Time; in The Climatic Factor; 
Carnegie Institution, 1914, p. 286. 


II. The contraction of the earth, as we have seen, has 
produced great changes in the distribution as well as in 
the extent of land and water. Large parts of the present 
continents have been covered repeatedly by the sea, and 
extensive areas now covered with water have been land. 
In recent geological times, that is, during the Pliocene and 
Pleistocene, much of the present continental shelf, the 
zone less than 600 feet below sea level, was land. If the 
whole shelf had been exposed, the lands would have been 
greater than at present by an area larger than North 
Ajnerica. When the lands were most elevated, or a little 
earlier. North America was probably connected with 
Asia and almost with Europe. Asia in turn was appar- 
ently connected with the larger East Indian islands. In 
much earlier times land occupied regions where now the 
ocean is fairly deep. Groups of islands, such as the East 
Indies and Malaysia and perhaps the West Indies, were 
united into widespreading land masses. Figs. 7 and 9, 
illustrating the paleography of the Permian and the 
Cretaceous periods, respectively, indicate a land distri- 
bution radically different from that of today. 

So far as appears from the scattered facts of geologi- 
cal history, the changes in the distribution of land seem 
to have been marked by the following characteristics : (1) 
Accompanying the differentiation of continental and 
oceanic segments of the earth's crust, the oceans have 
become somewhat deeper, and their basins perhaps 
larger, while the continents, on the average, have been 
more elevated and less subject to submergence. Hence 
there have been less radical departures from the present 
distribution during the relatively recent Cenozoic era 
than in the ancient Paleozoic because the submergence of 
continental areas has become less general and less fre- 
quent. For example, the last extensive epeiric or interior 


sea in North America was in the Cretaceous, at least ten 
million years ago, and according to Barrell perhaps fifty 
million, while in Europe, according to de Lapparent," a 
smaller share of the present continent has been sub- 
merged since the Cretaceous than before. Indeed, as in 
North America, the submergence has decreased on the 
average since the Paleozoic era. (2) The changes in dis- 
tribution of land which have taken place during earth 
history have been cyclic. Bepeatedly, at the close of each 
of the score or so of geologic periods, the continents 
emerged more or less, while at the close of the groups of 
periods known as eras, the lands were especially large 
and emergent. After each emergence, a gradual encroach- 
ment of the sea took place, and toward the close of sev- 
eral of the earlier periods, the sea appears to have 
covered a large fraction of the present land areas. (3) On 
the whole, the amount of land in the middle and high lati- 
tudes of the northern hemisphere appears to have in- 
creased during geologic time. Such an increase does not 
require a growth of the continents, however, in the 
broader sense of the term, but merely that a smaller 
fraction of the continent and its shelf should be sub- 
merged. (4) In tropical latitudes, on the other hand, the 
extent of the lands seems to have decreased, apparently 
by the growth of the ocean basins. South America and 
Africa are thought by many students to have been con- 
nected, and Africa was united with India via Mada- 
gascar, as is suggested in Fig. 9. The most radical cyclic 
as well as the most radical progressive changes in land 
distribution also seem to have taken place in tropical 
Although there is much evidence of periodic increase 

10 A. de Lapparent : Traits de GMog^e, 1906. 

17 Chas. Schuchert : Historical Qeology, 1915, p. 464. 



of the sea in equatorial latitudes and of land in high lati- 
tudes, it has remained for the zoologist Metcalf to pre- 
sent a very pretty bit of evidence that at certain times 
submergence along the equator coincided with emergence 
in high latitudes, and vice versa. Certain fresh water 
frogs which carry the same internal parasite are confined 
to two widely separated areas in tropical and south tem- 
perate America and in Australia. The extreme improba- 
bility that both the frogs and the parasites could have 
originated independently in two unconnected areas and 
could have developed by convergent evolution so that 
they are almost identical in the two continents makes it 
almost certain that there must have been a land con- 
nection between South America and Australia, presum- 
ably by way of Antarctica. The facts as to the parasites 
seem also to prove that while the land connection existed 
there was a sea across South America in equatorial lati- 
tudes. The parasite infests not only the frogs but the 
American toads known as Bufo. Now Bufo originated 
north of the equator in America and differs from the 
frogs which originated in southern South America in 
not being found in Australia. This raises the question of 
how the frogs could go to Australia via Antarctica carry- 
ing the parasite with them, while the toads could not go. 
Metcalf 's answer is that the toads were cut off from the 
southern part of South America by an equatorial sea 
until after the Antarctic connection between the Old 
World and the New was severed. 

As Patagonia let go of Antarctica by subsidence of the inter- 
vening land area, there was a probable concomitant rise of land 
through what is now middle South America and the northern 
and southern portions of this continent came together.^* 

18 M. M. Metcalf: Upon an important method of studying problems of 
relationship and of geographical distribution; Proceedings National Acad- 
emy of Sciences, Vol. 6, July, 1920, pp. 432-433. 


These various changes in the earth's crust have given 
rise to certain specific types of distribution of the lands, 
which will now be considered. We shall inquire what cli- 
matic conditions would arise from changes in (a) the 
continuity of the lands from north to south, (b) the 
amount of land in tropical latitudes, and (c) the amount 
of land in middle and high latitudes. 

(a) At present the westward drift of warm waters, set 
in motion by the trade winds, is interrupted by land 
masses and turned poleward, producing the important 
Gulf Stream Drift and Japan Current in the northern 
hemisphere, and corresponding, though less important, 
currents in the southern hemisphere. During the past, 
quite different sets of ocean currents doubtless have 
existed in response to a different distribution of land. 
Repeatedly, in the mid-Cretaceous (Fig. 9) and several 
other periods, the present American barrier to the west- 
ward-moving tropical current was broken in Central 
America. Even if the supposed continent of ' * Gondwana 
Land*' extended from Africa to South America in equa- 
torial latitudes, strong currents must still have flowed 
westward along its northern shore under the impulse of 
the peculiarly strong trade winds which the equatorial 
land would create. Nevertheless at such times relatively 
little warm tropical water presumably entered the North 
Atlantic, for it escaped into the Pacific. At several other 
times, such as the late Ordovician and mid-Devonian, 
when the isthmian barrier existed, it probably turned an 
important current northward into what is now the Mis- 
sissippi Basin instead of into the Atlantic. There it 
traversed an epeiric, or mid-continental sea open to both 
north and south. Hence its effectiveness in warming 
Arctic regions must have been quite different from that 
of the present Gulf Stream. 


(b) We will next consider the influences of changes in 
the amount of equatorial and tropical land. As such lands 
are much hotter than the corresponding seas, the inten- 
sity and width of the equatorial belt of low pressure must 
be great when they are extensive. Hence the trade winds 
must have been stronger than now whenever tropical 
lands were more extensive than at present. This is be- 
cause the trades are produced by the convection due to 
excessive heat along the heat equator. There the air 
expands upward and flows poleward at high altitudes. 
The trade wind consists of air moving toward the heat 
equator to take the place of the air which there rises. 
When the lands in low latitudes were wide the trade 
winds must also have dominated a wide belt. The greater 
width of the trade-wind belt today over Africa than over 
the Atlantic illustrates the matter. The belt must have 
been still wider when GK)ndwana Land was large, as it is 
believed to have been during the Paleozoic era and the 
early Mesozoic. 

An increase in the width of the equatorial belt of 
low pressure under the influence of broad tropical lands 
would be accompanied not only by stronger and more 
widespread trade winds, but by a corresponding strength- 
ening of the subtropical belts of high pressure. The chief 
reason would be the greater expansion of the air in the 
equatorial low pressure belt and the consequent more 
abundant outflow of air at high altitudes in the form of 
anti-trades or winds returning poleward above the trades. 
Such winds would pile up the air in the region of the high- 
pressure belt. Moreover, since the meridians converge as 
one proceeds away from the equator, the air of the pole- 
ward-moving anti-trades tends to be crowded as it 
reaches higher latitudes, thus increasing the pressure. 
Unless there were a corresponding increase in tropical 


cyclones, one of the most prominent results of the 
strengthened trades and the intensified subtropical high- 
pressure belt at times of broad lands in low latitudes 
would be great deserts. It will be recalled that the trade- 
wind lowlands and the extra-tropical belt of highs are the 
great desert belts at present. The trade-wind lowlands 
are desert because air moving into warmer latitudes 
takes up water except where it is cooled by rising on 
mountain-sides. The belt of highs is arid because there, 
too, air is being warmed, but in this case by descending 
from aloft. 

Again, if the atmospheric pressure in the subtropical 
belt should be intensified, the winds flowing poleward 
from this belt would necessarily become stronger. These 
would begin as southwesterlies in the northern hemi- 
sphere and northwesterlies in the southern. In the pre- 
ceding chapter we have seen that such winds, especially 
when cyclonic storms are few and mild, are a powerful 
agent in transferring subtropical heat poleward. If the 
strength of the westerlies were increased because of 
broad lands in low latitudes, their efficacy in transferring 
heat would be correspondingly augmented. It is thus 
evident that any change in the extent of tropical lands 
during the geologic past must have had important cli- 
matic consequences in changing the velocity of the 
atmospheric circulation and in altering the transfer of 
heat from low latitudes to high. When the equatorial and 
tropical lands were broad the winds and currents must 
have been strong, much heat must have been carried 
away from low latitudes, and the contrast between low 
and high latitudes must have been relatively slight. As 
we have already remarked, leading paleogeographers 
believe that changes in the extent of the lands have been 
especially marked in low latitudes, and that on the aver- 


age there has been a decrease in the extent of land within 
the tropics. Gk>ndwana Land is the greatest illnstration 
of this. In the same way, on the nnmerons paleogeo- 
graphic maps of North America, most paleogeographers 
have shown fairly extensive lands sonth of the latitude of 
the United States during most of the geologic epochs.^* 

(c) There is evidence that during geologic history the 
area of the lands in middle and high latitudes, as well as 
in low latitudes, has changed radically. An increase in 
such lands would cause the winters to grow colder. This 
would be partly because of the loss of heat by radiation 
into the cold dry air over the continents in winter, and 
partly because of increased reflection from snow and 
frost, which gather much more widely upon the land than 
upon the ocean. Furthermore, in winter when the conti- 
nents are relatively cold, there is a strong tendency for 
winds to blow out from the continent toward the ocean. 
The larger the land the stronger this tendency. In Asia 
it gives rise to strong winter monsoons. The effect of 
such winds is illustrated by the way in which the wester- 
lies prevent the Gulf Stream from warming the eastern 
United States in winter. The Gulf Stream warms north- 
western Europe much more than the United States be- 
cause, in Europe, the prevaUing winds are onshore. 

Another effect of an increase in the area of the lands in 
middle and high latitudes would be to interpose bar- 
riers to oceanic circulation and thus lower the tempera- 
ture of polar regions. This would not mean glaciation in 
high latitudes, however, even when the lands were wide- 
spread as in the Mesozoic and early Tertiary. Students 
of glaciology are more and more thoroughly convinced 

i^Chas. Schuchert: Paleogeography of North America; Bull. GeoL Soc. 
Am., Vol. 20, 1910; and Willis, Salisburj, and others: Outlines of Geologic 
History, 1910. 


that glaciation depends on the availability of moisture 
even more than upon low temperature. 

In conclusion it may be noted that each of the several 
climatic influences of increased land area in the high 
latitudes would tend to increase the contrasts between 
land and sea, between winter and summer, and between 
low latitudes and high. In other words, so far as the 
effect upon high latitudes themselves is concerned, an 
expansion of the lands there would tend in the same 
direction as a diminution in low latitudes. In so far as 
the general trend of geological evolution has been toward 
more land in high latitudes and less in low, it would help 
to produce a progressive increase in climatic diversity 
such as is faintly indicated in the rock strata. On the 
other hand, the oscillations in the distribution of the 
lands, of which geology affords so much evidence, must 
certainly have played an important part in producing the 
periodic changes of climate which the earth has under- 

in. Throughout geological history there is abundant 
evidence that the process of contraction has led to 
marked differences not only in the distribution and area 
of the lands, but in their height. On the whole the lands 
have presumably increased in height since the Protero- 
zoic, somewhat in proportion to the increased differentia- 
tion of continents and oceans.^^ If there has been such an 
increase, the contrast between the climate of ocean and 
land must have been accentuated, for highlands have a 
greater diurnal and seasonal range of temperature than 
do lowlands. The ocean has very little range of either 
sort. The large range at high altitudes is due chiefly to 
the small quantity of water vapor, for this declines 

so Chas. Schnchert : The Earth 's Changing Surface and Climate ; in Lull : 
The Evolution of the Earth and Its Inhabitants, 1918, p. 50. 


steadily with increased altitude. A diminution in the 
density of the other constituents of the air also decreases 
the blanketing effect of the atmosphere. In conformity 
with the great seasonal range in temperature at times 
when the lands stand high, the direction of the wind 
would be altered. When the lands are notably warmer 
than the oceans, the winds commonly flow from land to 
sea, and when the continents are much colder than the 
oceans, the direction is reversed. The monsoons of Asia 
are examples. Strong seasonal winds disturb the normal 
planetary circulation of the trade winds in low latitudes 
and of the westerlies in middle latitudes. They also inter- 
fere with the ocean currents set in motion by the planet- 
ary winds. The net result is to hinder the transfer of 
heat from low latitudes to high, and thus to increase the 
contrasts between the zones. Local as well as zonal con- 
trasts are also intensified. The higher the land, the 
greater, relatively speaking, are the cloudiness and pre- 
cipitation on seaward slopes, and the drier the interior* 
Indeed, most highlands are arid. Henry's*^ recent study 
of the vertical distribution of rainfall on mountain-sides 
indicates that a decrease sets in at about 3500 feet in the 
tropics and only a little higher in mid-latitudes. 

In addition to the main effects upon atmospheric cir- 
culation and precipitation, each of the many upheavals 
of the lands must have been accompanied by many minor 
conditions which tended toward diversity. For example, 
the streams were rejuvenated, and instead of meandering 
perhaps over vast flood plains they intrenched their 
channels and in many cases dug deep gorges. The water 
table was lowered, soil was removed from considerable 
areas, the bare rock was exposed, and the type of domi- 

21 A. J. Henry: The Deerease of Precipitation with Altitude; Monthlj 
Weather Beview, Vol. 47, 1919, pp. 33-41. 


nant vegetation altered in many places. An almost barren 
ridge may represent all that remains of what was once a 
vast forested flood plain. Thus, increased elevation of the 
land produces contrasted conditions of slope, vegetation, 
availability of ground water, exposure to wind and so 
forth, and these unite in diversifying climate. Where 
mountains are formed, strong contrasts are sure to 
occur. The windward slopes may be very rainy, while 
neighboring leeward slopes are parched by a dry foehn 
wind. At the same time the tops may be snow-covered. 
Increased local contrasts in climatic conditions are 
known to influence the intensity of cyclonic storms," and 
these affect the climatic conditions of all middle and high 
latitudes, if not of the entire earth. The paths followed 
by cyclonic storms are also altered by increased contrast 
between land and water. When the continents are notably 
colder than the neighboring oceans, high atmospheric 
pressure develops on the lands and interferes with the 
passage of lows, which are therefore either deflected 
around the continent or forced to move slowly. 

The distribution of lofty mountains has an even more 
striking climatic effect than the general uplift of a region. 
In Proterozoic times there was a great range in the Lake 
Superior region ; in the late Devonian the Acadian moun- 
tains of New England and the Maritime Provinces of 
Canada possibly attained a height equal to the present 
Eockies. Subsequently, in the late Paleozoic a significant 
range stood where the Ouachitas now are. Accompanying 
the uplift of each of these ranges, and all others, the 
climate of the surrounding area, especially to leeward, 
must have been altered greatly. Many extensive salt de- 

22Cha8. F. Brooks: Monthly Weather Eeview, Vol. 46, 1918, p. 511; and 
also A. J. Henry and others: Weather Forecasting in the United States, 


posits found now in fairly humid regions, for example, 
the Pennsylvanian and Permian deposits of Kansas and 
Oklahoma, were probably laid down in times of local 
aridity due to the cutting off of moisture-bearing winds 
by the mountains of Llanoria in Louisiana and Texas. 
Hence such deposits do not necessarily indicate periods 
of widespread and profound aridity. 

When the causes of ancient glaciation were first con- 
sidered by geologists, about the middle of the nineteenth 
century, it was usually assumed that the glaciated areas 
had been elevated to great heights, and thus rendered 
cold enough to permit the accumulation of glaciers. The 
many glaciers occurring in the Alps of central Europe 
where gladology arose doubtless suggested this explana- 
tion. However, it is now known that most of the ancient 
glaciation was not of the alpine type, and there is ade- 
quate proof that the glacial periods cannot be explained 
as due directly and solely to uplift. Nevertheless, up- 
heavals of the lands are among the most important fac- 
tors in controlling climate, and variations in the height 
of the lands have doubtless assisted in producing climate 
oscillations, especially those of long duration. Moreover, 
the progressive increase in the height of the lands has 
presumably played a part in fostering local and zonal 
diversity in contrast with the relative uniformity of 
earlier geological times. 

IV. The contraction of the earth has been accompanied 
by volcanic activity as well as by changes in the extent, 
distribution, and altitude of the lands. The probable part 
played by volcanic dust as a contributory factor in pro- 
ducing short sudden climatic variations has already been 
discussed. There is, however, another though probably 
less important respect in which volcanic activity may 
have had at least a slight climatic significance. The oldest 


known rocks, those of the Archean era, contain so much 
igneous matter that many students have assumed that 
they show that the entire earth was once liquid. It is now 
considered that they merely indicate igneous activity of 
great magnitude. In the later part of Proterozoic time, 
during the second quarter of the earth *s history accord- 
ing to Schuchert's estimate, there were again vast out- 
flowings of lava. In the Lake Superior district, for ex- 
ample, a thickness of more than a mile accumulated over 
a large area, and lavas are common in many areas where 
rocks of this age are known. The next quarter of the 
earth's history elapsed without any correspondingly 
great outflows so far as is known, though several lesser 
ones occurred. Toward the end of the last quarter, and 
hence quite recently from the geological standpoint, 
another period of outflows, perhaps as noteworthy as 
that of the Proterozoic, occurred in the Cretaceous and 

The climatic effects of such extensive lava flows would 
be essentially as follows : In the first place so long as the 
lavas were hot they would set up a local system of con- 
vection with inflowing winds. This would interfere at 
least a little with the general winds of the area. Again, 
where the lava flowed out into water, or where rain fell 
upon hot lava, there would be rapid evaporation which 
would increase the rainfall. Then after the lava had 
cooled, it would still influence climate a trifle in so far as 
its color was notably darker or lighter than that of the 
average surface. Dark surfaces absorb solar heat and 
become relatively warm when the sun shines upon them. 
Dark objects likewise radiate heat more rapidly than 
light-colored objects. Hence they cool more rapidly at 
night, and in the winter. As most lavas are relatively 
dark they increase the average diurnal range of tempera- 


tore. Hence even after they are cool they increase the 
climatic diversity of the land. 

The amount of heat given to the atmosphere by an 
extensive lava flow, though large according to human 
standards, is small compared with the amount received 
from the sun by a like area, except during the first few 
weeks or months before the lava has formed a thick 
crust. Furthermore, probably only a small fraction of 
any large series of flows occurred in a given century or 
millennium. Moreover, even the largest lava flows covered 
an area of only a few hundredths of one per cent of the 
earth's surface. Nevertheless, the conditions which mod- 
ify climate are so complicated that it would be rash to 
state that this amount of additional heat has been of 
no climatic significance. like the proverbial ** straw that 
broke the camel's back," the changes it would surely 
produce in local convection, atmospheric pressure, and 
the direction of the wind may have helped to shift the 
paths of storms and to produce other complications whidi 
were of appreciable climatic significance. 

V. The last point which we shall consider in connection 
with the effect of the earth's interior upon climate is 
internal heat The heat given off by lavas is merely a 
small part of that which is emitted by the earth as a 
whole. In the earliest part of geological history enough 
heat may have escaped from the interior of the earth to 
exert a profound influence on the climate. Ejiowlton,** 
as we have seen, has recently built up an elaborate theory 
on this assumption. At present, however, accurate meas- 
urements show that the escape of heat is so slight that 
it has no appreciable influence except in a few volcanic 

28 F. H. Knowlton: Evolution of Geologic Climates; BulL Oeol. See. Am.^ 
Vol. 30, Dec, 1919, pp. 499-566. 


areas. It is estimated to raise the average temperature 
of the earth's surface less than O.l'^C." 

In order to contribute enough heat to raise the surface 
temperature 1°0., the temperature gradient from the 
interior of the earth to the surface would need to be ten 
times as great as now, for the rate of conduction varies 
directly with the gradient. If the gradient were ten times 
as great as now, the rocks at a depth of two and one-half 
miles would be so hot as to be almost liquid according to 
Barrell's" estimates. The thick strata of unmetamor- 
phosed Paleozoic rocks indicate that such high tempera- 
tures have not prevailed at such slight depths since the 
Proterozoic. Furthermore, the fact that the climate was 
cold enough to permit gladation early in the Proterozoic 
era and at from one to three other times before the open- 
ing of the Paleozoic suggests that the rate of escape of 
heat was not rapid even in the first half of the earth's 
recorded history. Yet even if the general escape of heat 
has never been large since the beginning of the better- 
known part of geological history, it was prestmiably 
greater in early times than at present. 

If there actually has been an appreciable decrease in 
the amount of heat given out by the earth's interior, its 
effects would agree with the observed conditions of the 
geological record. It would help to explain the relative 
mildness of zonal, seasonal, and local contrasts of climate 
in early geological times, but it would not help to explain 
the long oscillations from era to era which appear to have 
been of much greater importance. Those oscillations, so 
far as we can yet judge, may have been due in part to 
solar changes, but in large measure they seem to be 

24 iTalbert, quoted by I. Bowman: Forest Physiography, 1911, p. 63. 
3s J. Barrell: Rhytiims and the Measurement of Geologic Time; BulL 
Geol. Soc. Am., Vol. 28, 1917, pp. 745-904. 


explained by variations in the extent, distribution, and 
altitude of the lands. Such variations appear to be the 
inevitable result of the earth 's contraction. 




A N interesting practical application of some of the 
/% preceding generalizations is found in an attempt 
1 \ by 0. E. P. Brooks^ to interpret post-glacial 
climatic changes almost entirely in terms of crustal move- 
ment. We believe that he carries the matter much too far, 
but his discussion is worthy of rather full recapitulation, 
not only for its theoretical value but because it gives a 
good summary of post-glacial changes. His climatic table 
for northwest Europe as reprinted from the annual re- 
port of the Smithsonian Institution for 1917, p. 366, is 
as follows : 





The Last Great Glaeia- 


Aretic climate. 

30,000-18,000 B. C. 


The Betreat of the 

Severe continental 



18,000-6000 B. C. 


The Ga&tinental Phase. 

Continental climate. 

6000-4000 B. C. 


The Maritime Phase. 

Warm and moist. 

4000-3000 B. C. 


The Later Forest Phase. 

Waim and dry. 

3000-1800 B. C. 


The Peat-Bog Phase. 

Cooler and moister. 

1800 B. C.-300 A. D. 


The Beeent Phase. 

Becoming drier. 

300 A. D.- 

Brooks bases his chronology largely on De (Jeer^s 
measurements of the annual layers of clay in lake 

1 C. E. P. Brooks : The Evolution of Climate in Northwest Europe. Quart. 
Jour. Boyal Meteorol. Soc, Vol, 47, 1921, pp. 173-194. 


bottoms but makes mnch use of other evidence. Accord- 
ing to Brooks the last glacial epoch lasted roughly from 
30,000 to 18,000 B. C, but this includes a slight ameliora- 
tion of climate followed by a readvance of the ice, known 
as the Buhl stage. During the time of maximum glacia- 
tion the British Isles stood twenty or thirty feet higher 
than now and Scandinavia was ** considerably'' more 
elevated. The author believes that this caused a fall of 
VG. in the temperature of the British Isles and of 2^C. 
in Scandinavia. By an ingenious though not wholly con- 
vincing method of calculation he concludes that this 
lowering of temperature, aided by an increase in the area 
of the lands, sufficed to start an ice sheet in Scandinavia. 
The relatively small area of ice cooled the air and gave 
rise to an area of high barometric pressure. This in turn 
is supposed to have caused further expansion of the ice 
and to have led to full-fledged glaciation. 

About 18,000 B. C. the retreat of the ice began in good 
earnest. Even though no evidence has yet been found, 
Brooks believes there must have been a change in the dis- 
tribution of land and sea to account for the diminution of 
the ice. The ensuing millenniums formed the Magdale- 
nian period in human history, the last stage of the Paleo- 
lithic, when man lived in caves and reindeer were abun- 
dant in central Europe.* At first the ice retreated very 
slowly and there were periods when for scores of years 
the ice edge remained stationary or even readvanced. 
About 10,000 B. C. the edge of the ice lay along the 
southern coast of Sweden. During the next 2000 years it 
withdrew more rapidly to about 59**N* Then came the 
Fennoscandian pause, or Gschnit^ stage, when for about 

2 H. F. Osbom: Men of the Old Stone Age, N. T., 1915; J. M. Tjrler: 
The New Stone Age in Northwestern Europe, N. T., 1920. 


200 years the ice edge remained in one position, forming 
a great moraine. Brooks suggests that this pause about 
8000 B. C. was due to the closing of the connection be- 
tween the Atlantic Ocean and the Baltic Sea and the 
synchronous opening of a connection between the Baltic 
and the White Seas, whereby cold Arctic waters replaced 
the warmer Atlantic waters. He notes, however, that 
about 7500 B. 0. the obliquity of the ecliptic was probably 
nearly 1** greater than at present. This he calculates to 
have caused the climate of Germany and Sweden to be 
VF. colder than at present in winter and 1°F. warmer in 

The next climatic stage was marked by a rise of tem- 
perature till about 6000 B. C. During this period the ice 
at first retreated, presumably because the climate was 
ameliorating, although no cause of such amelioration is 
assigned. At length the ice lay far enough north to allow 
a connection between the Baltic and the Atlantic by way 
of Lakes Wener and Wetter in southern Sweden. This is 
supposed to have warmed the Baltic Sea and to have 
caused the climate to become distinctly milder. Next the 
land rose once more so that the Baltic was separated 
from the Atlantic and was converted into the Ancylus 
lake of fresh water. The southwest Baltic region then 
stood 400 feet higher than now. The result was the Daun 
stage, about 5000 B. C, when the ice halted or perhaps 
readvanced a little, its front being then near Bagunda 
in about latitude 63°. Why such an elevation did not 
cause renewed glaciation instead of merely the slight 
Daun pause. Brooks does not explain, although his calcu- 
lations as to the effect of a slight elevation of the land 
during the main period of glaciation from 30,000 to 
18,000 B. C. would seem to demand a marked readvance. 


After 5000 B. C. there ensued a period when the cli- 
mate, although still distinctly continental, was relatively 
mild. The winters, to be sure, were stiU cold but the 
summers were increasingly warm. In Sweden, for ex- 
ample, the types of vegetation indicate that the smnmer 
temperature was 7°F. higher than now. Storms, Brooks 
assumes, were comparatively rare except on the outer 
fringe of Great Britain. There they were sufficiently 
abundant so that in the Northwest they gave rise to the 
first Peat-Bog period, during which swamps replaced 
forests of birch and pine. Southern and eastern England, 
however, probably had a dry continental climate. Even 
in northwest Norway storms were rare as is indicated by 
remains of forests on islands now barren because of the 
strong winds and fierce storms. Farther east most parts 
of central and northern Europe were relatively dry. This 
was the early Neolithic period when man advanced from 
the use of unpolished to polished stone implements. 

Not far from 4000 B. C. the period of continental cK- 
mate was replaced by a comparatively moist maritime 
climate. Brooks believes that this was because sub- 
mergence opened the mouth of the Baltic and caused the 
fresh Ancylus lake to give place to the so-called Litorina 
sea. The temperature in Sweden averaged about 3°F. 
higher than at present and in southwestern Norway 2**. 
More important than this was the small annual range of 
temperature due to the fact that the summers were cool 
while the winters were mild. Because of the presence of 
a large expanse of water in the Baltic region, storms, as 
our author states, then crossed Great Britain and fol- 
lowed the Baltic depression, carrying the moisture far 
inland. In spite of the additional moisture thus available 
the snow line in southern Norway was higher than now. 

At this point Brooks turns to other parts of the world. 


He states that not far from 4000 B. C, a submergence 
of the lands, rarely amounting to more than twenty-five 
feet, took place not only in the Baltic region but in Ire- 
land, Iceland, Spitzbergen, and other parts of the Arctic 
Ocean, as well as in the White Sea, Greenland, and the 
eastern part of North America. Evidences of a mild cli- 
mate are found in all those places. Similar evidence of a 
mild warm climate is found in East Africa, East Aus- 
tralia, Tierra del Fuego, and Antarctica. The dates are 
not established with certainty but* they at least fall in the 
period immediately preceding the present epoch. In ex- 
planation of these conditions Brooks assumes a universal 
change of sea level. He suggests with some hesitation 
that this may have been due to one of Pettersson's 
periods of maximum * * tide-generating force. ' ^ According 
to Pettersson the varying positions of the moon, earth, 
and sun cause the tides to vary in cycles of about 9, 90, 
and 1800 years, though the length of the periods is not 
constant. When tides are high there is great movement 
of oc^an waters and hence a great mixture of the water 
at different latitudes. This is supposed to cause an 
amelioration of climate. The periods of maximum and 
minimum tide-generating force are as follows : 

Maxima 3600 B. C. 2100 B. C. 350 B. C. A. D. 1434 

Minima 2800 B. C. 1200 B. C. A. D. 630 

Brooks thinks that the big trees in California and the 
Norse sagas and Germanic myths indicate a rough agree- 
ment of climatic phenomena with Pettersson 's last three 
dates, while the mild climate of 4000 B. C. may really 
belong to 3500 B. C. He gives no evidence confirming 
Pettersson 's view at the other three dates. 

To return to Brooks ' sketch of the relation of climatic 
pulsations to the altitude of the lands, by 3000 B. C, that 


is, toward the close of the Neolithic period, further eleva- 
tion is supposed to have taken place over the central 
latitudes of western Europe. Southern Britain, which had 
remained constantly above its present level ever since 
30,000 B. C, was perhaps ninety feet higher than now. 
Ireland was somewhat enlarged by elevation, the Straits 
of Dover were almost closed, and parts of the present 
North Sea were land. To these conditions Brooks ascribes 
the prevalence of a dry continental climate. The storms 
shifted northward once more, the winds were mild, as 
seems to be proved by remains of trees in exposed places ; 
and forests replaced fields of peat and heath in Britain 
and Germany. The summers were perhaps warmer than 
now but the winters were severe. The relatively dry cli- 
mate prevailed as far west as Ireland. For example, in 
Drumkelin Bog in Donegal County a corded oak road and 
a two-story log cabin appear to belong to this time. Four- 
teen feet of bog lie below the floor and twenty-six above. 
This period, perhaps 3000-2000 B. C, was the legendary 
heroic age of Ireland when **the vigour of the Irish 
reached a level not since attained." This, as Brooks 
points out, may have been a result of the relatively dry 
climate, for today the extreme moisture of Ireland seems 
to be a distinct handicap. In Scandinavia, civilization, or 
at least the stage of relative progress, was also high at 
this time. 

By 1600 B. C. the land had assumed nearly its pres- 
ent level in the British Isles and the southern Baltic 
region, while northern Scandinavia still stood lower than 
now. The climate of Britain and Germany was so humid 
that there was an extensive formation of peat even on 
high ground not before covered. This moist stage seems 
to have lasted almost to the time of Christ, and may have 
been the reason why the Romans described Britain as 


peculiarly wet and damp. At this point Brooks again de- 
parts from northwest Europe to a wider field : 

It is possible that we have to attribute this damp period in 
Northwest Europe to some more general cause, for Ellsworth 
Huntington's curves of tree-growth in California and climate 
in Western Asia both show moister conditions from about 
1000 B. C. to A. D. 200, and the same author believes that the 
Mediterranean lands had a heavier rainfall about 500 B. G. to 
A. D. 200. It seems that the phase was marked by a general in- 
crease of the storminess of the temperate regions of the northern 
hemisphere at least, with a maximum between Ireland and North 
Germany, indicating probably that the Baltic again became the 
favourite track of depressions from the Atlantic. 

Brooks ends his paper with a brief resume of glacial 
changes in North Ainerica, but as the means of dating 
events are unreliable the degree of synchronism with 
Europe is not clear. He sums up his conclusions as 
follows : 

On the whole it appears that though there is a general simi- 
larity in the climatic history of the two sides of the North 
Atlantic, the changes are not really contemporaneous, and such 
relationship as appears is due mainly to the natural similarity 
in the geographical history of two regions both recovering from 
an Ice Age, and only very partially to world-wide pulsations 
of climate. Additional evidence on this head will be available 
when Baron de Geer publishes the results of his recent investiga- 
tions of the seasonal glacial clays of North America, especially 
if, as he hopes, he is able to correlate the banding of these clays 
with the growth-rings of the big trees. 

When we turn to the northwest of North America, this is 
brought out very markedly. For in Yukon and Alaska the Ice 
Age was a very mild affair compared with its severity in eastern 
America and Scandinavia. As the land had not a heavy ice-load 
to recover from, there were no complicated geographical 


changes. Also, there were no fluctuations of climate, but simply 
a gradual passage to present conditions. The latter circumstance 
especially seems to show that the emphasis laid on geographical 
rather than astronomical factors of great climatic changes is 
not misplaced. 

Brooks ' painstaking discussion of post-glacial climatic 
changes is of great value because of the large body of 
material which he has so carefully wrought together. His 
strong belief in the importance of changes in the level of 
the lands deserves serious consideration. It is difficult, 
however, to accept his final conclusion that such changes 
are the main factors in recent climatic changes. It is al- 
most impossible, for example, to believe that movements 
of the land could produce almost the same series of 
climatic changes in Europe, Central Asia, the western 
and eastern parts of North America, and the southern 
hemisphere. Yet such changes appear to have occurred 
during and since the glacial period. Again there is no 
evidence whatever that movements of the land have any- 
thing to do with the historic cycles of climate or with the 
cycles of weather in our own day, which seem to be the 
same as glacial cycles on a small scale. Also, as Dr. 
Simpson points out in discussing Brooks' paper, there 
appears ^^no solution along these lines of the problem 
connected with rich vegetation in both polar circles and 
the ice-age which produced the ice-sheet at sea-level in 
Northern India. ' ' Nevertheless, we may well believe that 
Brooks is right in holding that changes in the relative 
level and relative area of land and sea have had im- 
portant local effects. While they are only one of the 
factors involved in climatic changes, they are certainly 
one that must constantly be kept in mind. 




HAVING discussed the climatic effect of move- 
ments of the earth's crust during the course of 
geological time, we are now ready to consider 
the corresponding effects due to changes in the movable 
envelopes — ^the oceans and the atmosphere. Variations in 
the composition of sea water and of air, and in the 
amount of air must ahnost certainly have occurred, and 
must have produced at least slight climatic consequences. 
It should be pointed out at once that such variations 
appear to be far less important climatically than do 
movements of the earth 's crust and changes in the activ- 
ity of the sun. Moreover, in most cases, they are not 
reversible as are the crustal and solar phenomena. Hence, 
while most of them appear to have been unimportant so 
far as climatic oscillations and fluctuations are concerned, 
they seemingly have aided in producing the slight secular 
progression to which we have so often referred. 

There is general agreement among geologists that the 
ocean has become increasingly saline throughout the 
ages. Indeed, calculations of the rate of accumulation of 
salt have been a favorite method of arriving at estimates 
of the age of the ocean, and hence of the earliest marine 
sediments. So far as known, however, no geologist or 
climatologist has discussed the probable climatic effects 


of increased salinity. Yet it seems clear that an increase 
in salinity must have a slight effect npon climate. 

Salinity affects climate in fonr ways: (1) It appre- 
ciably influences the rate of evaporation; (2) it alters 
the freezing point; (3) it produces certain indirect 
effects through changes in the absorption of carbon 
dioxide; and (4) it has an effect on oceanic circulation. 

(1) According to the experiments of Mazelle and 
Okada, as reported by Klriimmel,^ evaporation from ordi- 
nary sea water is from 9 to 30 per cent less rapid than 
from fresh water under similar conditions. The varia- 
tion from 9 to 30 per cent found in the experiments de- 
pends, perhaps, upon the wind velocity. When salt water 
is stagnant, rapid evaporation tends to result in the 
development of a film of salt on the top of the water, 
especially where it is sheltered from the wind. Such a film 
necessarily reduces evaporation. Hence the relatively 
low salinity of the oceans in the past probably had a 
tendency to increase the amount of water vapor in the 
air. Even a little water vapor augments slightly the 
blanketing effect of the air and to that extent diminishes 
the diurnal and seasonal range of temperature and the 
contrast from zone to zone. 

(2) Increased salinity means a lower freezing tem- 
perature of the oceans and hence would have an effect 
during cold periods such as the present and the Pleisto- 
cene ice age. It would not, however, be of importance 
during the long warm periods which form most of 
geologic time. A salinity of about 3.5 per cent at present 
lowers the freezing point of the ocean roughly 2°C. below 
that of fresh water. If the ocean were fresh and our 
winters as cold as now, all the harbors of New England 
and the Middle Atlantic States would be icebound. The 

1 Encyclopaedia Britannica, 11th edition: article "Ocean." 


Baltic Sea would also be frozen each winter, and even 
the eastern harbors of the British Isles would be fre- 
quently locked in ice. At high latitudes the area of per- 
manently frozen oceans would be much enlarged. The 
effect of such a condition upon marine life in high lati- 
tudes would be like that of a change to a warmer climate. 
It would protect the life on the continental shelf from the 
severe battering of winter storms. It would also lessen 
the severity of the winter temperature in the water for 
when water freezes it gives up much latent heat, — eighty 
calories per cubic centimeter. Part of this raises the 
temperature of the underlying water. 

The expansion of the ice near northern shores would 
influence the life of the lands quite differently from that 
of the oceans, It would act like an addition of land to the 
continents and would, therefore, increase the atmospheric 
contrasts from zone to zone and from continental interior 
to ocean. In summer the ice upon the sea would tend to 
keep the coastal lands cool, very much as happens now 
near the Arctic Ocean, where the ice floes have a great 
effect through their reflection of light and their absorp- 
tion of heat in melting. In winter the virtual enlargement 
of the continents by the addition of an ice fringe would 
decrease the snowfall upon the lands. Still more im- 
portant would be the effect in intensifying the anti- 
cyclonic conditions which normally prevail in winter not 
only over continents but over ice-covered oceans. Hence 
the outblowing cold winds would be strengthened.^ The 
net effect of all these conditions would apparently be a 
diminution of snowfall in high latitudes upon the lands 
even though the summer snowfall upon the ocean and the 

so. E. P. Brooks: The Meteorological Conditions of an Ice Sheet and 
Their Bearing on the Desiccation of the Globe; Quart. Jour. Bojal Meteorol. 
Soc., Vol. 40, 1914, pp. 53-70. 


coasts may have increased. This condition may have been 
one reason why widespread glaciation does not appear to 
have prevailed in high latitudes during the Proterozoic 
and Permian glaciations, even though it occurred farther 
south. If the ocean during those early glacial epochs 
were ice-covered down to middle latitudes, a lack of ex- 
tensive glaciation in high latitudes would be no more 
surprising than is the lack of Pleistocene glaciation in 
the northern parts of Alaska and Asia. Great ice sheets 
are impossible without a large supply of moisture. 

(3) Among the indirect effects of salinity one of the 
chief appears to be that the low salinity of the water in 
the past and the greater ease with which it froze presum- 
ably allowed the temperature of the entire ocean to be 
slightly higher than now. This is because ice serves as a 
blanket and hinders the radiation of heat from the under- 
lying water. The temperature of the ocean has a climatic 
sig3iificance not only directly, but indirectly through its 
influence on the amount of carbon dioxide held by the 
oceans. A change of even 1°C. from the present mean 
temperature of 2°C. would alter the ability of the entire 
ocean to absorb carbon dioxide by about 4 per cent. This, 
according to F. W. Clarke,' is because the oceans contain 
from eighteen to twenty-seven times as much carbon 
dioxide as the air when only the free carbon dioxide is 
considered, and about seventy times as much according 
to Johnson and Williamson* when the partially combined 
carbon dioxide is also considered. Moreover, the capacity 
of water for carbon dioxide varies sharply with the tem- 
perature.* Hence a rise in temperature of only 1®C. 
would theoretically cause the oceans to give up from 30 

• Data of GeochemiBtry, Fourth Ed., 1920; BulL No. 695, U. 8. OeoL 

* Quoted by Schuchert in The Evolution of the Earth. 

s Smithsonian Physical Tables, Sixth Bevision, 1914, p. 142. 


to 280 times as much carbon dioxide as the air now holds. 
This, however, is on the unfounded assumption that the 
oceans are completely saturated. The important point is 
merely that a slight change in ocean temperature would 
cause a disproportionately large change in the amount 
of carbon dioxide in the air with all that this impUes in 
respect to blanketing the earth, and thus altering tem- 

(4) Another and perhaps the most important effect of 
salinity upon climate depends upon the rapidity of the 
deep-sea circulation. The circulation is induced by differ- 
ences of temperature, but its speed is affected at least 
slightly by salinity. The vertical circulation is now domi- 
nated by cold water from subpolar latitudes. Except in 
closed seas like the Mediterranean the lower portions 
of the ocean are near the freezing point. This is because 
cold water sinks in high latitudes by reason of its su- 
perior density, and then ** creeps'' to low latitudes. There 
it finally rises and replaces either the water driven pole- 
ward by the winds, or that which has evaporated from 
the surface.* 

During past ages, when the sea water was less salty, 
the circulation was presumably more rapid than now. 
This was because, in tropical regions, the rise of cold 

<) Chamberlin, in a verj Buggestive article "On a possible reversal of 
oceanic circulation" (Jour, of G^L, Vol. 14, pp. 363-373, 1906), discusses 
the probable climatic consequences of a reversal in the direction of deep- 
flea circulation. It is not whoUj bejond the bounds of possibility that 
in the course of ages the increasing drainage of salt from the lands not 
onlj hy nature but by man's activities in agriculture and drainage, may 
ultimately cause such a reversal by increasing the ocean's salinity until the 
more saline tropical portion is heavier than the cooler but fresher subpolar 
waters. If that should happen, Greenland, Antarctica, and the northern 
shores of America and Asia would be warmed by the tropical heat which 
had been transferred poleward beneath the surface of the ocean, without 
lofls en route. Subpolar regions, under such a condition of reversed deep-sea 
eireulation, might have a mild climate. Indeed, they might be among the 
world's most favorable regions climatically. 


water is hindered by the sinMng of warm surface water 
which is relatively dense because evaporation has re- 
moved part of the water and caused an accumulation of 
salt. According to Kriimmel and Mill/ the surface salin- 
ity of the subtropical belt of the North Atlantic commonly 
exceeds 3.7 per cent and sometimes reaches 3.77 per cent, 
whereas the underlying waters have a salinity of less 
than 3.5 per cent and locally as little as 3.44 per cent 
The other oceans are slightly less saline than the North 
Atlantic at all depths^ but the vertical salinity gradients 
along the tropics are similar. According to the Smith- 
sonian Physical Tables, the difference in salinity between 
the surface water and that lying below is equivalent to 
a difference of .003 in density, where the density of fresh 
water is taken as 1.000. Since the decrease in density pro- 
duced by warming water from the temperature of its 
greatest density (4°C.) to the highest temperatures 
which ever prevail in the ocean (30°C. or SG^'F.) is only 
.004, the more saline surface waters of the dry tropics 
are at most times almost as dense as the less saline but 
colder waters beneath the surface, which have come from 
higher latitudes. During days of especially great evapo- 
ration, however, the most saline portions of the surface 
waters in the dry tropics are denser than the underlying 
waters and therefore sink, and produce a temporary local 
stagnation in the general circulation. Such a sinking of 
the warm surface waters is reported by Kriimmel, who 
detected it by means of the rise in temperature which it 
produces at considerable depths. If such a hindrance to 
the circulation did not exist, the velocity of the deep-sea 
movements would be greater. 

If in earlier times a more rapid circulation occurred, 
low latitudes must have been cooled more than now by 

7 Encydopcedia Britaxmica : article ' ' Ocean. ' ' 


the rise of cold waters. At the same time higher latitudes 
were presmnably warmed by a greater flow of warm 
water from tropical re^ons because less of the surface 
heat sank in low latitudes. Such conditions would tend to 
lessen the climatic contrast between the different lati- 
tudes. Hence, in so far as the rate of deep-sea circulation 
depends upon salinity, the slowly increasing amount of 
salt in the oceans must have tended to increase the con- 
trasts between low and high latitudes. Thus for several 
reasons, the increase of saUnity during geologic history 
seems to deserve a place among the minor agencies which 
help to explain the apparent tendency toward a secular 
progression of climate in the direction of greater con- 
trasts between tropical and subpolar latitudes. 

Changes in the composition and amount of the atmos- 
phere have presumably had a climatic importance greater 
than that of changes in the salinity of the oceans. The 
atmospheric changes may have been either progressive 
or cyclic, or both. In early times, according to the nebular 
hypothesis, the atmosphere was much more dense than 
now and contained a larger percentage of certain con- 
stituents, notably carbon dioxide and water. The plane- 
tesimal hypothesis, on the other hand, postulates an in- 
crease in the density of the atmosphere, for according to 
this hypothesis the density of the atmosphere depends 
upon the power of the earth to hold gases, and this power 
increases as the earth grows bigger with the infall of 
material from without.* 

Whichever hypothesis may be correct, it seems prob- 
able that when life first appeared on the land the at- 
mosphere resembled that of today in certain fundamental 
respects. It contained the elements essential to life, and 

8 Chamberlin and Salisbury: Geology, Vol. II, pp. 1-132, 1906; and T. C. 
Chamberlin: The Origin of the Earth, 1916. 


its blanketing effect was such as to maintain tempera- 
tures not greatly different from those of the present. The 
evidence of this depends largely upon the narrow limits 
of temperature within which the activities of modem 
life are possible, and upon the cumulative evidence that 
ancient life was essentiaUy similar to the types now 
living. The resemblance between some of the oldest 
forms and those of today is striking. For example, 
according to Professor Schuchert:* **Many of the living 
genera of forest trees had their origin in the Cretaceous, 
and the giant sequoias of California go back to the Trias- 
sic, while Ginkgo is known in the Permian. Some of the 
fresh-water molluscs certainly were living in the early 
periods of the Mesozoic, and the lung-fish of today 
(Ceratodus) is known as far back as the Triassic and is 
not very unlike other lung-fishes of the Devonian. The 
higher vertebrates and insects, on the other hand, are 
very sensitive to their environment, and therefore do not 
extend back generically beyond the Cenozoic, and only in 
a few instances even as far as the Oligocene. Of marine 
invertebrates the story is very different, for it is well 
known that the horseshoe crab (Limulus) lived in the 
Upper Jurassic, and Nautilus in the Triassic, with forms 
in the Devonian not far removed from this genus. Still 
longer-ranging genera occur among the brachiopods, for 
living Lingula and Crania have specific representatives 
as far back as the early Ordovician. Among living f ora- 
minifers, Lagena, Globigerina, and Nodosaria are known 
in the later Cambrian or early Ordovician. In the Middle 
Cambrian near Field, British Columbia, Walcott has 
found a most varied array of invertebrates among which 
are crustaceans not far removed from living forms. 
Zoologists who see these wonderful fossils are at once 

> Personal communication. 


struck with their modernity and the little change that has 
taken place in certain stocks since that far remote time. 
Back of the Paleozoic, little can be said of life from the 
generic standpoint, since so few fossils have been re- 
covered, but what is at hand suggests that the marine 
environment was similar to that of today. ' ' 

At present, as we have repeatedly seen, little growth 
takes place either among animals or plants at tempera- 
tures below 0°C. or above 40"* C, and for most species 
the limiting temperatures are about 10° and 30°. The 
maintenance of so narrow a scale of temperature is a 
function of the atmosphere, as well as of the sun. Without 
an atmosphere, the temperature by day would mount 
fatally wherever the sun rides high in the sky. By night 
it would fall everywhere to a temperature approaching 
absolute zero, that is — 273 °C. Some such tempera- 
ture prevails a few miles above the earth's surface, 
beyond the effective atmosphere. Indeed, even if the 
atmosphere were almost as it is now, but only lacked one 
of the minor constituents, a constituent which is often 
actually ignored in statements of the composition of the 
air, life would be impossible. Tyndall concludes that if 
water vapor were entirely removed from the atmosphere 
for a single day and night, all life — except that which is 
dormant 1 the form of seeds, eggs, or spores-would be 
exterminated. Part would be killed by the high tempera- 
ture developed by day when the sun was high, and part, 
by the cold night. 

The testimony of ancient glaciation as to the slight 
difference in the climate and therefore in the atmos- 
phere of early and late geological times is almost as clear 
as that of life. Just as life proves that the earth can never 
have been extremely cold during hundreds of millions of 
years, so glaciation in moderately low latitudes near 


the dawn of earth history and at several later times, 
proves that the earth was not particularly hot even in 
those early days. The gentle progressive change of climate 
which is recorded in the rocks appears to have been only 
in slight measure a change in the mean temperature of 
the earth as a whole, and almost entirely a change in the 
distribution of temperature from place to place and 
season to season. Hence it seems probable that neither 
the earth's own emission of heat, nor the supply of solar 
heat, nor the power of the atmosphere to retain heat can 
have been much greater a few hundred million years ago 
than now. It is indeed possible that these three factors 
may have varied in such a way that any variation in one 
has been offset by variations of the others in the opposite 
direction. This, however, is so highly improbable that it 
seems advisable to assume that all three have remained 
relatively constant. This conclusion together with a 
realization of the climatic significance of carbon dioxide 
has forced most of the adherents of the nebular hypothe- 
sis to abandon their assumption that carbon dioxide, the 
heaviest gas in the air, was very abundant until taken 
out by coal-forming plants or combined with the calcium 
oxide of igneous rocks to form the limestone secreted 
by animals. In the same way the presence of sun cracks 
in sedimentary rocks of all ages suggests that the air 
cannot have contained vast quantities of water vapor 
such as have been assumed by Knowlton and others in 
order to account for the former lack of sharp climatic 
contrast between the zones. Such a large amount of water 
vapor would ahnost certainly be accompanied by well- 
nigh universal and continual cloudiness so that there 
would be little chance for the pools on the earth 's water- 
soaked surface to dry up. Furthermore, there is only one 
way in which such cloudiness could be maintained and 


that is by keeping the air at an ahnost constant tempera- 
ture night and day. This would require that the chief 
source of warmth be the interior of the earth, a condition 
which the Proterozoic, Permian, and other widespread 
glaciations seem to disprove. 

Thus there appears to be strong evidence against the 
radical changes in the atmosphere which are sometimes 
postulated. Yet some changes must have taken place, and 
even minor changes would be accompanied by some sort 
of climatic effect. The changes would take the form of 
either an increase or a decrease in the atmosphere as a 
whole, or in its constituent elements. The chief means by 
which the atmosphere has increased appear to be as 
follows: (a) By contributions from the interior of the 
earth via volcanoes and springs and by the weathering of 
igneous rocks with the consequent release of their en- 
closed gases ;^® (b) by the escape of some of the abundant 
gases which the ocean holds in solution ; (c) by the arrival 
on the earth of gases from space, either enclosed in 
meteors or as free-flying molecules; (d) by the release of 
gases from organic compounds by oxidation, or by ex- 
halation from animals and plants. On the other hand, one 
or another of the constituents of the atmosphere has pre- 
sumably decreased (a) by being locked up in newly 
formed rocks or organic compounds; (b) by being dis- 
solved in the ocean; (c) by the escape of molecules into 
space; and (d) by the condensation of water vapor. 

The combined effect of the various means of increase 
and decrease depends partly on the amount of each con- 
stituent received from the earth's interior or from space, 
and partly on the fact that the agencies which tend to 
deplete the atmosphere are highly selective in their 

10 B. T. Chamberlin : Oases in Bocks, Carnegie Inst, of Wash., No. 106, 


action. Our knowledge of how large a quantity of new 
gases the air has received is very scanty, but judging by 
present conditions the general tendency is toward a slow 
increase chiefly because of meteorites, volcanic action, 
and the work of deep-seated springs. As to decrease, the 
case is clearer. This is because the chemically active 
gases, oxygen, CO2, and water vapor, tend to be locked 
up in the rocks, while the chemically inert gases, nitrogen 
and argon, show almost no such tendency. Though oxy- 
gen is by far the most abimdant element in the earth's 
crust, making up more than 50 per cent of the total, it 
forms only about one-fifth of the air. Nitrogen, on the 
other hand, is very rare in the rocks, but makes up nearly 
four-fifths of the air. It would, therefore, seem probable 
that throughout the earth's history, there has been a 
progressive increase in the amount of atmospheric nitro- 
gen, and presumably a somewhat corresponding increase 
in the mass of the air. On the other hand, it is not clear 
what changes have occurred in the amount of atmos- 
pheric oxygen. It may have increased somewhat or 
perhaps even notably. Nevertheless, because of the 
greater increase in nitrogen, it may form no greater per- 
centage of the air now than in the distant past. 

As to the absolute amounts of oxygen, Barrell" 
thought that atmospheric oxygen began to be present 
only after plants had appeared. It will be recalled that 
plants absorb carbon dioxide and separate the carbon 
from the oxygen, using the carbon in their tissues and 
setting free the oxygen. As evidence of a paucity of 
oxygen in the air in early Proterozoic times, Barrell 
cites the fact that the sedimentary rocks of that remote 

11 J. Barrell : The Origin of the Earth, in Evolution of the Earth and 
Its Inhabitants, 1918, p. 44, and more fully in an unpublished manuaeript. 


time commonly are somewhat greyish or greenish-grey 
wackesy or other types, indicating incomplete oxidation. 
He admits, however, that the stupendous thicknesses of 
red sandstones, quartzite, and hematitic iron ores of the 
later Proterozoic prove that by that date there was an 
abundance of atmospheric oxygen. If so, the change from 
paucity to abundance must have occurred before fossils 
were numerous enough to give much clue to climate. 
However, Barrell's evidence as to a former paucity of 
atmospheric oxygen is not altogether convincing. In the 
first place, it does not seem justifiable to assume that 
there could be no oxygen until plants appeared to break 
down the carbon dioiide, for some oxygen is contributed 
by volcanoes,** and lightning decomposes water into its 
elements. Part of the hydrogen thus set free escapes into 
space, for the earth's gravitative force does not appear 
great enough to hold this lightest of gases, but the oxy- 
gen remains. Thus electrolysis of water results in the 
accumulation of oxygen. In the second place, there is no 
proof that the ancient greywackes are not deoxidized 
sediments. Light colored rock formations do not neces- 
sarily indicate a paucity of atmospheric oxygen, for such 
rocks are abundant even in recent times. For example, 
the Tertiary formations are characteristically light 
colored, a result, however, of deoxidation. Finally, the 
fact that sedimentary rocks, irrespective of their age, 
contain an average of about 1.5 per cent more oxygen 
than do igneous rocks," suggests that oxygen was pres- 
ent in the air in quantity even when the earliest shales 
and sandstones were formed, for atmospheric oxygen 
seems to be the probable source of the extra oxygen they 

12 p. W. Clarke: Data of Geochemistry, Fourth Ed., 1920, Bull. No. 695, 
U. S. GeoL Survey, p. 256. 

"P. W. Clarke: loc. cit,, pp. 27-34 et al. 


contain. The formation of these particular sedimentary 
rocks by weathering of igneous rocks involves only a 
little carbon dioxide and water. Although it seems prob- 
able that oxygen was present in the atmosphere even at 
the beginning of the geological record, it may have been 
far less abundant then than now. It may have been re- 
moved from the atmosphere by animals or by the oxida- 
tion of the rocks almost as rapidly as it was added by 
volcanoes, plants, and other agencies. 

After this chapter was in typBy St. John*" announced 
his interesting discovery that oxygen is apparently lack- 
ing in the atmosphere of Venus. He considers that this 
proves that Venus has no life. Furthermore he concludes 
that so active an element as oxygen cannot be abundant 
in the atmosphere of a planet unless plants continually 
supply large quantities by breaking down carbon dioxide. 

But even if the earth has experienced a notable in- 
crease in atmospheric oxygen since the appearance of 
life, this does not necessarily involve important dimatic 
changes except those due to increased atmospheric den- 
sity. This is because oxygen has very little effect upon 
the passage of light or heat, being transparent to all but 
a few wave lengths. Those absorbed are chiefly in the 
ultra violet. 

The distinct possibility that oxygen has increased in 
amount, makes it the more likely that there has been an 
increase in the total atmosphere, for the oxygen would 
supplement the increase in the relatively inert nitrogen 
and argon, which has presumably taken place. The cli- 
matic effects of an increase in the atmosphere include, in 
the first place, an increased scattering of light as it 
approaches the earth. Nitrogen, argon, and oxygen all 

i<* Chas. E. St. John : Science Service Press Reports from the Mt. Wilson 
Observatory, May, 1922, 


scatter the short waves of light and thus interfere with 
their reaching the earth. Abbot and Fowle," who have 
carefully studied the matter, believe that at present the 
scattering is quantitatively important in lessening insola- 
tion. Hence our supposed general increase in the volume 
of the air during part of geological times would tend to 
reduce the amount of solar energy reaching the earth's 
surface. On the other hand, nitrogen and argon do not 
appear to absorb the long wave lengths known as heat, 
and oxygen absorbs so little as to be almost a non- 
absorber. Therefore the reduced penetration of the air 
by solar radiation due to the scattering of light would 
apparently not be neutralized by any direct increase in 
the blanketing effect of the atmosphere, and the tempera- 
ture near the earth's surface would be slightly lowered 
by a thicker atmosphere. This would diminish the amount 
of water vapor which would be held in the air, and 
thereby lower the temperature a trifle more. 

In the second place, the higher atmospheric pressure 
which would result from the addition of gases to the 
air would cause a lessening of the rate of evaporation, 
for that rate declines as pressure increases. Decreased 
evaporation would presumably still further diminish the 
vapor content of the atmosphere. This would mean a 
greater daily and seasonal range of temperature, as is 
very obvious when we compare clear weather with cloudy. 
Cloudy nights are relatively warm while clear nights are 
cool, because water vapor is an almost perfect absorber 
of radiant heat, and there is enough of it in the air on 
moist nights to interfere greatly with the escape of the 
heat accumulated during the day. Therefore, if atmos- 

1^ Abbot and Fowle: Annals Astrophyaical Observatoiy; Smiths. Inst., 
Vol. II, 1908, p. 163. 

F. £. Fowle: Atmospheric Scattering of Light; Misc. Coll. Smiths. Inst., 
Vol. 69, 1918. 


pheric moisture were formerly much more abundant 
than noWy the temperature must have been much more 
uniform. The tendency toward climatic severity as time 
went on would be still further increased by the cooling 
which would result from the increased wind velocity dis- 
cussed below; for cooling by convection increases with 
the velocity of the wind, as does cooling by conduction. 

Any persistent lowering of the general temperature of 
the air would affect not only its ability to hold water 
vapor, but would produce a lessening in the amount of 
atmospheric carbon dioxide, for the colder the ocean 
becomes the more carbon dioxide it can hold in solution. 
When the oceanic temperature falls, part of the atmos- 
pheric carbon dioxide is dissolved in the ocean. This 
minor constituent of the air is important because 
although it forms only 0.003 per cent of the earth's at- 
mosphere, Abbot and Fowle *s" calculations indicate that 
it absorbs over 10 per cent of the heat radiated outward 
from the earth. Hence variations in the amount of carbon 
dioxide may have caused an appreciable variation in 
temperature and thus in other climatic conditions. 
Humphreys, as we have seen, has calculated that a 
doubling of the carbon dioxide in the air would directly 
raise the earth's temperature to the extent of 1.3*^0., and 
a halving would lower it a like amount. The indirect 
results of such an increase or decrease might be greater 
than the direct results, for the change in temperature 
due to variations in carbon dioxide would alter the 
capacity of the air to hold moisture. 

Two conditions would especially help in this respect; 
first, changes in nocturnal cooling, and second, changes 
in local convection. The presence of carbon dioxide dimin- 
ishes nocturnal cooling because it absorbs the heat radi- 

iB Abbot and Fowle: loc. dt., p. 172. 


ated by the earth, and re-radiates part of it back again. 
Hence with increased carbon dioxide and with the 
consequent wanner nights there would be less nocturnal 
condensation of water vapor to form dew and frost. 
Local convection is influenced by carbon dioxide because 
this gas lessens the temperature gradient. In general, the 
less the gradient, that is, the less the contrast between 
the temperature at the surface and higher up, the less 
convection takes place. This is illustrated by the seasonal 
variation in convection. In summer, when the gradient is 
steepest, convection reaches its maximum. It will be re- 
called that when air rises it is cooled by expansion, and 
if it ascends far the moisture is soon condensed and 
precipitated. Indeed, local convection is considered by 
C. P. Day to be the chief agency which keeps the lower 
air from being continually saturated with moisture. The 
presence of carbon dioxide lessens convection because it 
increases the absorption of heat in the zone above the 
level in which water vapor is abundant, thus warming 
these higher layers. The lower air may not be warmed 
correspondingly by an increase in carbon dioxide if 
Abbot and Fowle are right in stating that near the earth's 
surface there is enough water vapor to absorb practicaUy 
all the wave lengths which carbon dioxide is capable of 
absorbing. Hence carbon dioxide is chiefly effective at 
heights to which the low temperature prevents water 
vapor from ascending. Carbon dioxide is also effective 
in cold winters and in high latitudes when even the lower 
air is too cold to contain much water vapor. Moreover, 
carbon dioxide, by altering the amount of atmospheric 
water vapor, exerts an indirect as well a& a direct effect 
upon temperature. 

Other effects of the increase in air pressure which we 
are here asstmiing during at least the early part of geo- 


logical times are corresponding changes in barometric 
contrasts, in the strength of winds, and in the mass of air 
carried by the winds along the earth's surface. The in- 
crease in the mass of the air would reenf orce the greater 
velocity of the winds in their action as eroding and trans- 
porting agencies. Because of the greater weight of the 
air, the winds would be capable of picking up more dust 
and of carrying it farther and higher; while the increased 
atmospheric friction would keep it aloft a longer time. 
The significance of dust at high levels and its relation to 
solar radiation have already been discussed in connection 
with volcanoes. It will be recalled that on the average it 
lowers the surface temperature. At lower levels, since 
dust absorbs heat quickly and gives it out quickly, its 
presence raises the temperature of the air by day and 
lowers it by night. Hence an increase in dustiness tends 
toward greater extremes. 

-From all these considerations it appears that if the 
atmosphere has actually evolved according to the suppo- 
sition which is here tentatively entertained, the general 
tendency of the resultant climatic changes must have 
been partly toward long geological oscillations and partly 
toward a general though very slight increase in climatic 
severity and in the contrasts between the zones. This 
seems to agree with the geological record, although the 
fact that we are living in an age of relative climatic 
severity may lead us astray. 

The significant fact about the whole matter is that the 
three great types of terrestrial agencies, namely, those 
of the earth's interior, those of the oceans, and those of 
the air, all seem to have suffered changes which lead to 
slow variations of climate. Many reversals have doubt- 
less taken place, and the geologic oscillations thus in- 
duced are presumably of much greater importance than 


the progressive diangey yet so far as we can tell the 
purely terrestrial changes throughout the hundreds of 
millions of years of geological time have tended toward 
complexity and toward increased contrasts from conti- 
nent to ocean, from latitude to latitude, from season to 
season, and from day to night. 

Throughout geological history the slow and almost 
imperceptible differentiation of the earth's surface has 
been one of the most noteworthy of all changes. It has 
been opposed by the extraordinary conservatism of the 
universe which causes the average temperature today to 
be so like that of hundreds of millions of years ago that 
many types of life are almost identical. Nevertheless, the 
differentiation has gone on. Often, to be sure, it has pre- 
sumably been completely masked by the disturbances of 
the solar atmosphere which appear to have been the 
cause of the sharper, shorter climatic pulsations. But 
regardless of cosmic conservatism and of solar impulses 
toward change, the slow differentiation of the earth's 
surface has apparently given to the world of today much 
of the geographical complexity which is so stimulating 
a factor in organic evolution. Such complexity — such 
diversity from place to place — appears to be largely 
accounted for by purely terrestrial causes. It may be 
regarded as the great terrestrial contribution to the 
climatic environment which guides the development of 


IF solar activity is really an important factor in 
causing climatic changes, it behooves us to subject 
the sun to the same kind of inquiry to which we 
have subjected the earth. We have inquired into the na- 
ture of the changes through which the earth *s crust, the 
oceans, and the atmosphere have influenced the climate 
of geological times. It has not been necessary, however, 
to study the origin of the earth, nor to trace its earlier 
stages. Our study of the geological record begins only 
when the earth had attained practically its present mass, 
essentially its present shape, and a climate so similar to 
that of today that life as we know it was possible. In 
other words, the earth had passed the stages of infancy, 
childhood, youth, and early maturity, and had reached 
full maturity. As it still seems to be indefinitely far from 
old age, we infer that during geological times its relative 
changes have been no greater than those which a man 
experiences between the ages of perhaps twenty-five and 

Similar reasoning applies with equal or greater force 
to the sun. Because of its vast size it presumably passes 
through its stages of development much more slowly than 
the earth. In the first chapter of this book we saw that 
the earth 's relative uniformity of climate for hundreds of 
millions of years seems to imply a similar uniformity in 
solar activity. This accords with a recent tendency among 


astronomers who are more and more recognizing that the 
stars and the solar system possess an extraordinary de- 
gree of conservatism. Changes that once were supposed 
to take place in thousands of years are now thought to 
have required millions. Hence in this chapter we shall 
assume that throughout geological times the condition 
of the sun has been almost as at present. It may have 
been somewhat larger, or different in other ways, but it 
was essentially a hot, gaseous body such as we see today 
and it gave out essentially the same amount of energy. 
This assumption will affect the general validity of what 
follows only if it departs widely from the truth. With this 
assumption, then, let us inquire into the degree to which 
the sun's atmosphere has probably been disturbed 
throughout geological times. 

In Earth and Sun, as already explained, a detailed 
study has led to the conclusion that cyclonic storms are 
influenced by the electrical action of the sun. Such ac- 
tion appears to be most intense in sunspots, but appar- 
ently pertains also to other disturbed areas in the sun 's 
atmosphere. A study of sunspots suggests that their 
true periodicity is almost if not exactly identical with 
that of the orbital revolution of Jupiter, 11.8 years. Other 
investigations show numerous remarkable coincidences 
between sunspots and the orbital revolution of the other 
planets, including especially Saturn and Mercury. This 
seems to indicate that there is some truth in the hypothe- 
sis that sunspots and other related disturbances of the 
solar atmosphere owe their periodicity to the varying 
effects of the planets as they approach and recede from 
the sun in their eccentric orbits and as they combine or 
oppose their effects according to their relative positions. 
This does not mean that the energy of the solar disturb- 
ances is supposed to come from the planets, but merely 


that their variations act Uke the turning of a switch to 
determine when and how violently the internal forces of 
the sun shall throw the solar atmosphere into commotion. 
This hypothesis is by no means new, for in one form or 
another it has been advocated by Wolfer, Birkeland, 
E. W. Brown, Schuster, Arctowski, and others. 

The agency through which the planets influence the 
solar atmosphere is not yet clear. The suggested agencies 
are the direct pull of gravitation, the tidal effect of the 
planets, and an electro-magnetic effect. In Earth and 
Sun the conclusion is reached that the first two are out 
of the question, a conclusion in which E. W. Brown 
acquiesces. Unless some unknown cause is appealed to, 
this leaves an electro-magnetic hypothesis as the only one 
which has a reasonable foundation. Schuster inclines to 
this view. The conclusions set forth in Earth and Sun as 
to the electrical nature of the sun^s influence on the earth 
point somewhat in the same direction. Hence in this 
chapter we shall inquire what would happen to the sun, 
and hence to the earth, on their journey through space, 
if the solar atmosphere is actually subject to disturbance 
by the electrical or other effects of other heavenly bodies. 
It need hardly be pointed out that we are here venturing 
into highly speculative ground, and that the verity or 
falsity of the conclusions reached in this chapter has 
nothing to do with the validity of the reasoning in pre- 
vious chapters. Those chapters are based on the assump- 
tion that terrestrial causes of climatic changes are sup- 
plemented by solar disturbances which produce their 
effect partly through variations in temperature but also 
through variations in the intensity and paths of cyclonic 
storms. The present chapter seeks to shed some light on 
the possible causes and sequence of solar disturbances. 

Let us begin by scanning the available evidence as to 


solar disturbances previous to the time when accurate 
sunspot records are available. Two rather slender bits of 
evidence point to cycles of solar activity lasting hundreds 
of years. One of these has already been discussed in 
Chapter VI, where the climatic stress of the fourteenth 
century was described. At that time sunspots are known 
to have been imusually numerous, and there were great 
climatic extremes. Lakes overflowed in Central Asia; 
storms, droughts, floods, and cold winters were unusually 
severe in Europe; the Caspian Sea rose with great 
rapidity; the trees of California grew with a vigor un- 
known for centuries ; the most terrible of recorded fam- 
ines occurred in England and India; the Eskimos were 
probably driven south by increasing snowiness in Green- 
land; and the Mayas of Yucatan appear to have made 
their last weak attempt at a revival of civilization under 
the stimulus of greater storminess and less constant 

The second bit of evidence is foun4 in recent ex- 
haustive studies of periodicities by Turner^ and other 
astronomers. They have sought every possible natural 
occurrence for which a numerical record is available for 
a long period. The most valuable records appear to be 
those of tree growth, Nile floods, Chinese earthquakes, 
and sunspots. Turner reaches the conclusion that all four 
types of phenomena show the same periodicity, namely, 
cycles with an average length of about 260 to 280 years. 
He suggests that if this is true, the cycles in tree growth 
and in floods, both of which are climatic, are probably 
due to a non-terrestrial cause. The fact that the sunspots 

1 H. H. Turner: On a Long Period in Chinese Earthquake Beeords; Mon. 
Not. Boyal Astron. Soc., Vol. 79, 1919, pp. 531-539; VoL 80, 1920, pp. 617- 
619; Long Period Terms in the Growth of Trees; idem, pp. 793-808. 


show similar cycles suggests that the sun^s variations 
are the cause. 

These two bits of evidence are far too slight to form 
the foundation of any theory as to changes in solar 
activity in the geological past. Nevertheless it may be 
helpful to set forth certain possibilities as a stimulus to 
further research. For example, it has been suggested that 
meteoric bodies may have fallen into the sun and caused 
it suddenly to flare up, as it were. This is not impossible, 
although it does not appear to have taken place since 
men became advanced enough to make careful observa- 
tions. Moreover, the meteorites which now fall on the 
earth are extremely small, the average size being com- 
puted as no larger than a grain of wheat. The largest 
ever found on the earth *s surface, at Bacubirito in 
Mexico, weighs only about fifty tons, while within the 
rocks the evidences of meteorites are extremely scanty 
and insignificant. If meteorites had fallen into the sun 
often enough and of sufficient size to cause glacial fluctua- 
tions and historic pulsations of climate, it seems highly 
probable that the earth would show much more evidence 
of having been similarly disturbed. And even if the sun 
should be bombarded by large meteors the result would 
probably not be sudden cold periods, which are the most 
notable phenomena of the earth's climatic history, but 
sudden warm periods followed by slow cooling. Neverthe- 
less, the disturbance of the sun by collision with meteoric 
matter can by no means be excluded as a possible cause 
of climatic variations. 

Allied to the preceding hypothesis is Shapley's* nebu- 
lar hypothesis. At frequent intervals, averaging about 

2 Harlow Shapley: Note on a Posedble Factor in Geologic Climatee; 
Jonr. Geol., Vol. 29, No. 4, May, 1921; Notsb and Variable Stare, Pub. 
Astron. Soc. Pac, No. 194, Aug., 1921. 


once a year during the last thirty years, astronomers have 
discovered what are known as novae. These are stars 
which were previously faint or even invisible, bnt which 
flash suddenly into brilliancy. Often their light-giving 
power rises seven or eight magnitudes— a thousand-fold. 
In addition to the spectacular novae there are numerous 
irregular variables whose briUiancy changes in every 
ratio from a few per cent up to several magnitudes. Most 
of them are located in the vicinity of nebulae, as is also 
the case with novae. This, as well as other facts, makes it 
probable that all these stars are * * friction variables, ' ' as 
Shapley calls them. Apparently as they pass through the 
nebulae they come in contact with its highly diffuse 
matter and thereby become bright much as the earth 
would become bright if its atmosphere were filled with 
millions of almost infinitesimally small meteorites. A star 
may also lose brilliancy if nebulous matter intervenes 
between it and the observer. If our sun has been sub- 
jected to any of these changes some sort of climatic effect 
must have been produced. 

In a personal communication Shapley amplifies the 
nebular climatic hypothesis as follows : 

Within 700 light years of the sun in many directions (Taurus, 
Cygnus, Ophiuchus, Scorpio) are great diffuse clouds of nebu- 
losity, some bright, most of them dark. The probability that stars 
moving in the general region of such clouds will encounter this 
material is very high, for the clouds fill enormous volumes of 
space, — e.g., probably more than a hundred thousand cubic light 
years in the Orion region, and are presumably composed of rare- 
fied gases or of dust particles. Probably throughout all our 
part of space such nebulosity exists (it is all around us, we are 
sure), but only in certain regions is it dense enough to affect 
conspicuously the stars involved in it. If a star moving at high 
velocity should collide with a dense part of such a nebulous 


cloud, we should probably have a typical nova. If the relative 
velocity of nebulous material and star were low or moderate, or 
if the material were rare, we should not expect a conspicuous 
effect on the star's light. 

In the nebulous region of Orion, which is probably of un- 
usually high density, there are about 100 known stars, varying 
between 20% and 80% of their total light — aU of them irregu- 
larly — some slowly, some suddenly. Apparently they are 
''friction variables." Some of the variables suddenly lose 40% 
of their light as if blanketed by nebulous matter. In the Trifid 
Nebula there are variables like those of Orion, in Messier 8 also, 
and probably many of the 100 or so around the Bho Ophiuchi 
region belong to this kind. 

I believe that our sun could not have been a typical nova, at 
least not since the Archeozoic, that is for perhaps a billion years. 
I believe we have in geological climates final proof of this, be- 
cause an increase in the amount of solar radiation by 1000 times 
as in the typical nova, would certainly punctuate emphatically 
the life cycle on the earth, even if the cause of the nova would 
not at the same time eliminate the smaller planets. But the sun 
may have been one of these miniature novae or friction vari- 
ables; and I believe it very probable that its wanderings through 
this part of space could not long leave its mean temperature 
unaffected to the amount of a few per cent. 

One reason we have not had this proposal insisted upon 
before is that the data back of it are mostly new — ^the Orion 
variables have been only recently discovered and studied, the 
distribution and content of the dark nebulae are hardly as yet 
generally known. 

This interesting hypothesis cannot be hastily dis- 
missed. If the sun should pass through a nebula it seems 
inevitable that there would be at least slight climatic 
effects and perhaps catastrophic effects through the 
action of the gaseous matter not only on the sun but on 
the earth's own atmosphere. As an explanation of the 


general climatic conditions of the past, however, Shapley 
points out that the hypothesis has the objection of being 
vagae, and that nebulosity should not be regarded as 
more than **a possible factor/' One of the chief difficul- 
ties seems to be the enormously wide distribution of as 
yet undiscovered nebulous matter which must be assumed 
if any large share of the earth's repeated climatic 
changes is to be ascribed to such matter. If such matter 
is actually abimdant in space, it is hard to see how any 
but the nearest stars would be visible. Another objection 
is that there is no known nebulosity near at hand with 
which to connect the climatic vicissitudes of the last 
glacial period. Moreover, the known nebulae are so much 
less numerous than stars that the chances that the sun 
will encounter one of them are extremely slight. This, 
however, is not an objection, for Shapley points out that 
during geological times the sun can never have varied 
as much as do the novae, or even as most of the friction 
variables. Thus the hypothesis stands as one that is worth 
investigating, but that cannot be finally rejected or ac- 
cepted until it is made more definite and until more in- 
formation is available. 

Another suggested cause of solar variations is the rela- 
tively sudden contraction of the sun such as that which 
sometimes occurs on the earth when continents are up- 
lifted and mountains upheaved. It seems improbable that 
this could have occurred in a gaseous body like the sun. 
Lacking, as it does, any solid crust which resists a change 
of form, the sun probably shrinks steadily. Hence any 
climatic effects thus produced must be extremely gradual 
and must tend steadily in one direction for millions of 

Still another suggestion is that the tidal action of the 
stars and other bodies which may chance to approach 





the sun's path may cause disturbances of the solar 
atmosphere. The vast kaleidoscope of space is never 
quiet. The sun, the stars, and all the other heavenly- 
bodies are moving, often with enormous speed. Hence the 
effect of gravitation upon the sun must vary constantly 
and irregularly, as befits the geological requirements. In 
the case of the planets, however, the tidal effect does not 
seem competent to produce the movements of the solar 
atmosphere which appear to be concerned in the incep- 
tion of sunspots. Moreover, there is only the most remote 
probability that a star and the sun will approach near 
enough to one another to produce a pronounced gravita- 
tional disturbance in the solar atmosphere. For instance, 
if it be assumed that changes in Jupiter's tidal effect on 
the sun are the main factor in regulating the present dif- 
ference between sunspot maxima and sunspot minima, 
the chances that a star or some non-luminous body of 
similar mass will approach near enough to stimulate 
solar activity and thereby bring on glaciation are only 
one in twelve billion years, as will be explained below. 
This seems to make a gravitational hypothesis im- 

Another possible cause of solar disturbances is that 
the stars in their flight through space may exert an 
electrical influence which upsets the equilibrium of the 
solar atmosphere. At first thought this seems even more 
impossible than a gravitational effect. Electrostatic 
effects, however, differ greatly from those of tides. They 
vary as the diameter of a body instead of as its mass; 
their differentials also vary inversely as the square of 
the distance instead of as the cube. Electrostatic effects 
also increase as the fourth power of the temperature or 
at least would do so if they followed the law of black 
bodies ; they are stimulated by the approach of one body 


to another; and they are cumulative, for if ions arrive 
from space they must accumulate until the body to which 
they have come begins to discharge them. Hence, on the 
basis of assumptions such as those used in the preceding 
paragraph, the chances of an electrical disturbance of 
the solar atmosphere sufficient to cause glaciation on the 
earth may be as high as one in twenty or thirty million 
years. This seems to put an electrical hypothesis within 
the bounds of possibility. Further than that we cannot 
now go. There may be other hypotheses which fit the facts 
much better, but none seems yet to have been suggested. 

In the rest of this chapter the tidal and electrical 
hypotheses of stellar action on the sun will be taken up 
in detail. The tidal hypothesis is considered because in 
discussions of the effect of the planets it has hitherto 
held almost the entire field. The electrical hypothesis will 
be considered because it appears to be the best yet sug- 
gested, although it still seems doubtful whether electrical 
effects can be of appreciable importance over such vast 
distances as are inevitably involved. The discussion of 
both hypotheses will necessarily be somewhat technical, 
and will appeal to the astronomer more than to the lay- 
man. It does not form a necessary part of this book, for 
it has no bearing on our main thesis of the effect of the 
sun on the earth. It is given here because ultimately the 
question of changes in solar activity during geological 
times must be faced. 

In the astronomical portion of the following discus- 
sion we shall follow Jeans' in his admirable attempt at a 
mathematical analysis of the motions of the universe. 
Jeans divides the heavenly bodies into five main types: 
(1) Spiral nebulae, which are thought by some astrono- 

sj. H. Jeans: Problems of Cosmogony and Stellar Dynamics, 0am- 
bridge, 1919. 


mers to be systems like our own in the making, and by 
others to be independent universes lying at vast distances 
beyond the limits of our Galactic universe, as it is called 
from the Galaxy or Milky Way. (2) Nebulae of a smaller 
type, called planetary. These lie within the Galactic por- 
tion of the universe and seem to be early stages of what 
may some day be stars or solar systems. (3) Binary or 
multiple stars, which are extraordinarily numerous. In 
some parts of the heavens they form 50 or even 60 per 
cent of the stars and in the galaxy as a whole they seem to 
form ** fully one third.'* (4) Star clusters. These consist 
of about a hundred groups of stars in each of which the 
stars move together in the same direction with approxi- 
mately the same velocity. These, like the spiral nebulae, 
are thought by some astronomers to lie outside the limits 
of the galaxy, but this is far from certain. (5) The solar 
system. According to Jeans this seems to be unique. It 
does not fit into the general mathematical theory by 
which he explains spiral nebulae, planetary nebulae, binary 
stars, and star clusters. It seems to demand a special 
explanation, such as is furnished by tidal disruption due 
to the passage of the sun close to another star. 

The part of Jeans ' work which specially concerns us is 
his study of the probability that some other star will 
approach the sun closely enough to have an appreciable 
gravitative or electrical effect, and thus cause disturb- 
ances in the solar atmosphere. Of course both the star 
and the sun are moving, but to avoid circumlocution we 
shall speak of such mutual approaches simply as ap- 
proaches of the sun. For our present purpose the most 
fundamental fact may be summed up in a quotation from 
Jeans in which he says that most stars ^^show evidence 
of having experienced considerable disturbance by other 
systems ; there is no reason why our solar system should 



be expected to have escaped the common fate." Jeans 
gives a careful calculation from which it is possible to 
derive some idea of the probability of any given degree of 
approach of the sun and some other star. Of course all 
such calculations must be based on certain assumptions. 
The assumptions made by Jeans are such as to make the 
probability of close approaches as great as possible. For 
example, he allows only 560 million years for the entire 
evolution of the sun, whereas some astronomers and 
geologists would put the figure ten or more times as 
high. Nevertheless, Jeans* assumptions at least show 
the order of magnitude which we may expect on the basis 
of reasonable astronomical conclusions. 

According to the planetary hypothesis of sunspots, the 
difference in the effect of Jupiter when it is nearest and 
farthest from the sun is the main factor in starting the 

sunspot cycle and hence the corresponding terrestrial 

cycle. The climatic difference between sunspot maxima \ 
and minima, as measured by temperature, apparently ; ,. 
amounts to at least a twentieth and perhaps a tenth of / / *' 
the difference between the climate of the last glacial / 
epoch and the present. We may suppose, then, that a body ^ ^ 
which introduced a gravitative or electrical factor twenty ' 
times as great as the difference in Jupiter's effect at its 
maximum and minimum distances from the sun would ,' 
cause a glacial epoch if the effect lasted long enough. Of \ 
course the other planets combine their effects with that / 
of Jupiter, but for the sake of simplicity we will leave 
the others out of account. The difference between Jupi- 
ter's maximum and minimum tidal effect on the sun 
amounts to 29 per cent of the planet's average effect. 
The corresponding difference, according to the electrical 
hypothesis, is about 19 per cent, for electrostatic action 
varies as the square of the distance instead of as the cube. 


Let us assume that a body exerting four times Jupiter's 
present tidal effect and placed at the average distance of 
Jupiter from the sun would disturb the sun^s atmosphere 
twenty times as much as the present difference between 
sunspot maxima and minima, and thus, perhaps, cause a 
glacial period on the earth. 

On the basis of this assumption our first problem is to 
estimate the frequency with which a star, visible or 
dark, is likely to approach near enough to the sun to 
produce a tidaX effect four times that of Jupiter. The 
number of visible stars is known or at least well esti- 
mated. As to dark stars, which have grown cool, Arrhe- 
nius believed that they are a hundred times as numerous 
as bright stars; few astronomers believe that there are 
less than three or four times as many. Dr. Shapley of 
the Harvard Observatory states that a new investigation 
of the matter suggests that eight or ten is probably a 
maximum figure. Let us assume that nine is correct. 
The average visible star, so far as measured, has a mass 
about twice that of the sun, or about 2100 times that of 
Jupiter. The distances of the stars have been measured 
in hundreds of cases and thus we can estimate how many 
stars, both visible and invisible, are on an average con- 
tained in a given volume of space. On this basis Jeans 
estimates that there is only one chance in thirty billion 
years that a visible star will approach within 2.8 times 
the distance of Neptune from the sun, that is, within about 
eight billion miles. If we include the invisible stars the 
chances become one in three billion years. In order to 
produce four times the tidal effect of Jupiter, however, 
the average star would have to approach within about 
four billion miles of the sun, and the chances of that 
are only one in twelve billion years. The disturbing star 


would be only 40 per cent farther from the sun than 
Neptune, and would almost pass within the solar system. , 

Even though Jeans holds that the frequency of the ? 
mutual approach of the sun and a star was probably ( i\ 
much greater in the distant past than at present, the 
figures just given lend little support to the tidal hypothe- 
sis. In fact, they apparently throw it out of court. It will 
be remembered that Jeans has made assumptions which 
give as high a frequency of stellar encounters as is con- 
sistent with the astronomical facts. We have assumed 
nine dark stars for every bright one, which may be a 
liberal estimate. Also, although we have assumed that a 
disturbance of the sun's atmosphere sufficient to cause 
a glacial period would arise from a tidal effect only \ 
twenty times as great as the difference in Jupiter's effect 
when nearest the sun and farthest away, in our computa- 
tions this has actually been reduced to thirteen. With aU 
these favorable assumptions the chances of a stellar ap- 
proach of the sort here described are now only one in 
twelve billion years. Yet within a hundred million years, ( 
according to many estimates of geological time, and \ 
almost certainly within a billion, there have been at least 
half a dozen glaciations. 

Our use of Jeans' data interposes another and equally 
insuperable difficulty to any tidal hypothesis. Four bil- 
lion miles is a very short distance in the eyes of an 
astronomer. At that distance a star twice the size of the 
sun would attract the outer planets more strongly than 
the sun itself, and might capture them. If a star should 
come within four billion miles of the sun, its effect in 
distorting the orbits of all the planets would be great. 
If this had happened often enough to cause all the gla- 
ciations known to geologists, the planetary orbits would 
be strongly elliptical instead of almost circular. The con- 



siderations here advanced militate so strongly against 
the tidal hypothesis of solar disturbances that it seems 
scarcely worth while to consider it further. 

Let us turn now to the electrical hypothesis. Here the 
conditions are fundamentally different from those of the 
tidal hypothesis. In the first place the electrostatic effect 
of a body has nothing to do with its mass, but depends on 
the area of its surface ; that is, it varies as the square of 
the radius. Second, the emission of electrons varies ex- 
ponentially. If hot glowing stars follow the same law as 
black bodies at lower temperatures, the emission of 
electrons, like the emission of other kinds of energy, 
varies as the fourth power of the absolute temperature. 
In other words, suppose there are two black bodies, other- 
wise alike, but one with a temperature of 2V C. or 300° 
on the absolute scale, and the other with 600° on the 
absolute scale. The temperature of one is twice as high 
as that of the other, but the electrostatic effect will be 
sixteen times as great.* Third, the number of electrons 

^This fact is so important and at the same time so surprising to the 
lajman, that a quotation from The Electron Theory of Matter by O. W. 
Bichardson, 1914, pp. 326 and 334 is here added. 

''It is a very familiar fact that when material bodies are heated they 
emit electromagnetic radiations, in the form of thermal, luminous, and 
actinic rays, in appreciable quantities. Such an effect is a natural consequence 
of the electron and kinetic theories of matter. On the kinetic theory, tem- 
perature is a measure of the yiolence of the motion of the ultimate par- 
tides; and we have seen that on the electron theory, electromagnetic 
radiation is a consequence of their acceleration. The calculation of tills 
emission from the standpoint of the electron theory alone is a very complex 
problem which takes us deeply into the structure of matter and which has 
probably not yet been satisfactorily resolved. Fortunately, we can find out 
a great deal about these phenomena by the application of general prin- 
ciples like the conservation of energy and the second law of thermo- 
dynamics without considering special assumptions about the ultimate con- 
stitution of matter. It is to be borne in mind that the emission under 
consideration occurs at all temperatures although it is more marked the 
higher the temperature. . . . The energy per unit volume, in vacuo, of the 
radiation in equilibrium in an enclosure at the absolute temperature, T, is 
equal to a universal constant. A, multiplied by the fourth power of the 


that reach a given body varies inversely as the square of 
the distance, instead of as the cube which is the case 
with tide-making forces. 

In order to use these three principles in calculating 
the effect of the stars we must know the diameters, dis- 
tances, temperature, and number of the stars. The dis- 
tances and number may safely be taken as given by Jeans 
in the calculations already cited. As to the diameters, the 
measurements of the stars thus far made indicate that 
the average mass is about twice that of the sun. The 
average density, as deduced by Shapley* from the move- 
ments of double stars, is about one-eighth the solar 
density. This would give an average diameter about two 
and a half times that of the sun. For the dark stars, we 
shall assume for convenience that they are ten times as 
numerous as the bright ones. We shall also assume that 
their diameter is half that of the sun, for being cool they 
must be relatively dense, and that their temperature is 
the same as that which we shall assume for Jupiter. 

As to Jupiter we shall continue our former assumption 
that a body with four times the effectiveness of that 
planet, which here means with twice as great a radius, 
would disturb the sun enough to cause glaciation. It 
would produce about twenty times the electrostatic effect 

absolute temperature. Since the intensitj of the radiation is equal to the 
energy per unit yolume multiplied bj the velocitj of light, it follows that 
the former must also be proportionid to the fourth power of the absolute 
temperature. Moreover, if E is the total emission from unit area of a 
perfectly black body, we see from p. 330 that E=A'T«, where A' is a new 
universal constant. This result is usually known as Stefan's Law. It was 
suggested by Stefan in the inaccurate form that the total radiant energy 
of emission from bodies varies as the fourth power of the absolute tempera- 
ture, as a generalization from the results of experiments. The credit for 
showing that it is a consequence of the existence of radiation pressure 
oombined with the principles of thermodynamics is due to BartoU and 
Boltzmann. ' ' 

8 Quoted by Moulton in his Introduction to Astronomy. 


which now appears to be associated with the difference in 
Jupiter's effect at maximum and minimum. The tempera- 
ture of Jupiter must also be taken into account. The 
planet is supposed to be hot because its density is low, 
being only about 1.25 that of water. Nevertheless, it is 
probably not luminous, for as Moulton* puts it, shadows 
upon it are black and its moons show no sign of illumina- 
tion except from the sun. Hence a temperature of about 
600° C, or approximately 900** on the absolute scale, 
seems to be tiie highest that can reasonably be assigned 
to the cold outer layer whence electrons are emitted. As 
to the temperature of the sun, we shall adopt the conmion 
estimate of about GSOO^'C. on the absolute scale. The 
other stars will be taken as averaging the same, although 
of course they vary greatly. 

When Jeans' method of calculating the probability of 
a mutual approach of the sun and a star is applied to the 
assumptions given above, the results are as shown in 
Table 5. On that basis the dark stars seem to be of 
negligible importance so far as the electrical hypothesis 
is concerned. Even though they may be ten times as 
numerous as the bright ones there appears to be only 
one chance in 130 billion years that one of them will ap- 
proach the sun closely enough to cause the assumed dis- 
turbance of the solar atmosphere. On the other hand, if 
all the visible stars were the size of the sun, and as hot 
as that body, their electrical effect would be fourfold 
that of our assumed dark star because of their size, and 
2401 times as great because of their temperature, or ap- 
proximately 10,000 times as great. Under such conditions 
the theoretical chance of an approach that would cause 
glaciation is one in 130 million years. If the average 
visible star is somewhat cooler than the sun and has a 

8 Introduction to Astronomy. 


radius about two and one-half times as great, as appears 
to be the fact, the chances rise to one in thirty-eight mil- 
lion years. A slight and wholly reasonable change in our 
assumptions would reduce this last figure to only five or 
ten million. For instance, the earth's mean temperature 
during the glacial period has been assumed as lO^'C. 
lower than now, but the difference may have been only 6"^. 
Again, the temperature of the outer atmosphere of Jupi- 
ter where the electrons are shot out may be only 500° or 
700° absolute, instead of 900°. Or the diameter of the 
average star may be five or ten times that of the sun, 
instead of only two and one-half times as great. All this, 
however, may for the present be disregarded. The essen- 
tial point is that even when the assumptions err on the 
side of conservatism, the results are of an order of magni- 
tude which puts the electrical hypothesis within the 
bounds of possibility, whereas similar assumptions put 
the tidal hypothesis, with its single approach in twelve 
billion years, far beyond those limits. 

The figures for Betelgeuse in Table 5 are interesting. 
At a meeting of the American Association for the Ad- 
vancement of Science in December, 1920, Michelson 
reported that by measurements of the interference of 
light coming from the two sides of that bright star in 
Orion, the observers at Mount Wilson had confirmed the 
recent estimates of three other authorities that the star 's 
diameter is about 218 million miles, or 250 times that of 
the Sim. If other stars so much surpass the estimates of 
only a decade or two ago, the average diameter of all the 
visible stars must be many times that of the sun. The low 
figure for Betelgeuse in section D of the table means that 
if all the stars were as large as Betelgeuse, several might 
often be near enough to cause profound disturbances of 
the solar atmosphere. Nevertheless, because of the low 







Dark stars 





A. Approximate 
radius in miles 





B. Assumed tem- 
perature above 
absolute zero.. 

900° C. 

6300° C. 

5400° C. 

3150° C. 

0. Approximate 
theoretical dis- 
tance at which 
star would 
cause solar dis- 
turbance great 
enough to cause 
glaciation (bil- 
lions^ of miles). 





D. Average in- 
terval between 
close enough to 
cause glacia- 
tion if all stars 
were of given 
type. Years.. 





temperature of the giant red stars of the Betelgeuse type, 
the distance at which one of them would produce a given 
electrical effect is only about five times the distance at 
which our assumed average star would produce the same 
effect. This, to be sure, is on the assumption that the 

7 The term billions, here and elsewhere, is used in the American senaey lO^. 
> The assumed number of stars here is ten times as great as in the other 
parts of this line. 


radiation of energy from incandescent bodies varies 
according to temperature in the same ratio as the radia- 
tion from black bodies. Even if this assumption departs 
somewhat from the truth, it still seems almost certain 
that the lower temperature of the red compared with the 
high temperature of the wMte stars must to a consider- 
able degree reduce the difference in electrical effect which 
would otherwise arise from their size. 

Thus far in our attempt to estimate the distance at 
which a star might disturb the sun enough to cause gla- 
ciation on the earth, we have considered only the star's 
size and temperature. No account has been taken of the 
degree to which its atmosphere is disturbed. Yet in the 
case of the sun this seems to be one of the most important 
factors. The magnetic field of sunspots is sometimes 50 
or 100 times as strong as that of the sun in general. The 
strength of the magnetic field appears to depend on the 
strength of the electrical currents in the solar atmos- 
phere. But the intensity of the sunspots and, by inference, 
of the electrical currents, may depend on the electrical 
action of Jupiter and the other planets. If we apply a 
similar line of reasoning to the stars, we are at once led 
to question whether the electrical activity of double stars 
may not be enormously greater than that of isolated 
stars like the sun. 

If this line of reasoning is correct, the atmosphere of 
every double star must be in a state of commotion vastly 
greater than that of the sun's atmosphere even when it 
is most disturbed. For example, suppose the sun were 
accompanied by a companion of equal size at a distance 
of one million miles, which would make it much like many 
known double stars. Suppose also that in accordance with 
the general laws of physics the electrical effect of the 
two suns upon one another is proportional to the fourth 


power of the temperature, the square of the radius, and 
the inverse square of the distance. Then the effect of each 
sun upon the other would be sixty billion (6 x 10^^) times 
as great as the present electrical effect of Jupiter upon 
the sun. Just what this would mean as to the net effect 
of a pair of such suns upon the electrical potential of 
other bodies at a distance we can only conjecture. The 
outstanding fact is that the electrical conditions of a 
double star must be radically different and vastly more 
intense than those of a single star like the sun. 

This conclusion carries weighty consequences. At pres- 
ent twenty or more stars are known to be located within 
about 100 trillion miles of the sun (five par sees, as the 
astronomers say), or 16.5 light years. According to the 
assumptions employed in Table 5 an average single star 
would influence the sun enough to cause glaciation if it 
came within approximately 200 billion miles. If the star 
were double, however, it might have an electrical capacity 
enormously greater than that of the sun. Then it would 
be able to cause glaciation at a correspondingly great 
distance. Today Alpha Centauri, the nearest known star, 
is about twenty-five trillion miles, or 4.3 light years from 
the sun, and Sirius, the brightest star in the heavens, is 
about fifty trillion miles away, or 8.5 light years. If these 
stars were single and had a diameter three times that of 
the sun, and if they were of the same temperature as has 
been assumed for Betelgeuse, which is about fifty times as 
far away as Alpha Centauri, the relative effects of the 
three stars upon the sun would be, approximately, Betel- 
geuse 700, Alpha Centauri 250, Sirius 1. But Alpha Cen- 
tauri is triple and Sirius double, and both are much hotter 
than Betelgeuse. Hence Alpha Centauri and even Sirius 
may be far more effective than Betelgeuse. 

The two main components of Alpha Centauri are sepa- 


rated by an average distance of about 2,200,000,000 miles, 
or somewhat less than that of Neptmie from the sim. A 
third and far fainter star, one of the faintest yet meas- 
ured, revolves around them at a great distance. In mass 
and brightness the two main components are about like 
the sun, and we will assume that the same is true of their 
radius. Then, according to the assumptions made above, 
their effect in disturbing one another electrically would 
be about 10,000 times the total effect of Jupiter upon the 
sun, or 2500 times the effect that we have assumed to be 
necessary to produce a glacial period. We have already 
seen in Table 5 that, according to our assumptions, a 
single star like the sim would have to approach within 
120 billion miles of the solar system, or within 2 per cent 
of a light year, in order to cause glaciation. By a similar 
process of reasoning it appears that if the mutual elec- 
trical excitation of the two main parts of Alpha Centauri, 
regardless of the third part, is proportional to the ap- 
parent excitation of the sun by Jupiter, Alpha Centauri 
would be 5000 times as effective as the sun. In other 
words, if it came within 8,500,000,000,000 miles of the sun, 
or 1.4 light years, it would so change the electrical condi- 
tions as to produce a glacial epoch. In that case Alpha 
Centauri is now so near that it introduces a disturbing 
effect equal to about one-sixth of the effect needed to 
cause glaciation on the earth. Sirius and perhaps others 
of the nearer and brighter or larger stars may also create 
appreciable disturbances in the electrical condition of the 
sun's atmosphere, and may have done so to a much 
greater degree in the past, or be destined to do so in the 
future. Thus an electrical hypothesis of solar disturb- 
ances scenes to indicate that the position of the sun in 
respect to other stars may be a factor of great impor- 
tance in determining the earth's climate. 



HAVING gained some idea of the nature of the 
electrical hypothesis of solar disturbances and 
of the possible effect of other bodies upon the 
sun's atmosphere, let us now compare the astronomical 
data with those of geology. Let us take up five chief 
points for which the geologist demands an explanation^ 
and which any hypothesis must meet if it is to be per- 
manently accepted. These are (1) the irregular intervals 
at which glacial periods occur; (2) the division of glacial 
periods into epochs separated sometimes by hundreds 
of thousands of years; (3) the length of glacial periods 
and epochs; (4) the occurrence of glacial stages and his- 
toric pulsations in the form of small climatic waves 
superposed upon the larger waves of glacial epochs ; (5) 
the occurrence of climatic conditions much milder than 
those of today, not only in the middle portion of the great 
geological eras, but even in some of the recent inter- 
glacial epochs. 

1. The irregular duration of the interval from one 
glacial epoch to another corresponds with the irregular 
distribution of the stars. If glaciation is indirectly due 
to stellar influences, the epochs might fall close together, 
or might be far apart. If the average interval were ten 
million years, one interval might be thirty million or 
more and the next only one or two hundred thousand. 


According to Schuchert, the known periods of glacial or 
semi-glacial climate have been approximately as follows : 


1. Archeozoic. 

(^ of geological time or perhaps much more) 

No known glacial periods. 

2. Proterosoic. 

(% of geological time) 

a. Oldest known glacial period near base of Proterozoic in 
Canada. Evidence widely distributed. 

b. Indian glacial period; time unknown. 

c. African glacial period; time unknown. 

d. Glaciation near end of Proterozoic in Australia, Norway, 
and China. 

3. Paleozoic. 

(% of geological time) 

a. Late OrdoTician(f). Local in Arctic Norway. 

b. Silurian. Local in Alaska. 

c. Early Devonian. Local in South Africa. 

d. Early Permian. World-wide and very severe. 

4. Mesozoic and Cenozoic. 
(% of geological time) 

a-b. None definitely determined during Mesozoic, although 
there appears to have been periods of cooling (a) in the 
late Triassic, and (b) in the late Oretacic, with at least 
local glaciation in early Eocene. 

c. Severe glacial period during Pleistocene. 

This table suggests an interesting inquiry. During the 
last few decades there has been great interest in ancient 
glaciation and geologists have carefully examined rocks 
of all ages for signs of glacial deposits. In spite of the 
large parts of the earth which are covered with deposits 
belonging to the Mesozoic and Cenozoic, which form the 


I last quarter of geological time, the only signs of actual 

glaciation are those of the great Pleistocene period and a 
few local occurrences at the end of the Mesozoic or be- 

I ginning of the Cenozoic. Late in the Triassic and early 

in the Jurassic, the dinaate appears to have been rigor- 
ous, although no tillites have been found to demonstrate 
glaciation. In the preceding quarter, that is, the Paleo- 
zoic, the Permian glaciation was more severe than that 
of the Pleistocene, and the Devonian than that of the 
Eocene, while the Ordovician evidences of low tempera- 
ture are stronger than those at the end of the Triassic. 
In view of the fact that rocks of Paleozoic age cover 
much smaller areas than do those of later age, the three 
Paleozoic glaciations seem to indicate a relative fre- 
quency of glaciation. Going back to the Proterozoic, it 
is astonishing to find that evidence of two highly de- 
veloped glacial periods, and possibly four, has been dis- 
covered. Since the Indian and the African glaciations of 
Proterozoic times are as yet undated, we cannot be sure 
that they are not of the same date as the others. Never- 
theless, even two is a surprising number, for not only 
are most Proterozoic rocks so metamorphosed that pos- 
sible evidences of glacial origin are destroyed, but rocks 
of that age occupy far smaller areas than either those 
of Paleozoic or, still more, Mesozoic and Cenozoic age. 
Thus the record of the last three-quarters of geological 
time suggests that if rocks of all ages were as abundant 
and as easily studied as those of the later periods, the 
frequency of glacial periods would be found to increase 
as one goes backward toward the beginnings of the 
earth's history. This is interesting, for Jeans holds that 
the chances that the stars would approach one another 
were probably greater in the past than at present. This 
conclusion is based on the assumption that our universe 


is like the spiral nebulae in which the orbits of the varions 
members are nearly circular during the younger stages. 
Jeans considers it certain that in such cases the orbits 
will gradually become larger and more elliptical because 
of the attraction of one body for another. Thus as time 
goes on the stars will be more widely distributed and 
the chances of approach will diminish. K this is correct, 
the agreement between astronomical theory and geologi- 
cal conclusions suggests that the two are at least not in 

The first quarter of geological time as well as the last 
three must be considered in this connection. During the 
Archeozoic, no evidence of glaciation has yet been dis- 
covered. This suggests that the geological facts disprove 
the astronomical theory. But our Imowledge of early 
geological times is extremely limited, so limited that 
lack of evidence of glaciation in the Archeozoic may have 
no significance. Archeozoic rocks have been studied 
minutely over a very small percentage of the earth's land 
surface. Moreover, they are highly metamorphosed so 
that, even if glacial tills existed, it would be hard to 
recognize them. Third, according to both the nebular and 
the planetesimal hypotheses, it seems possible that 
during the earliest stages of geological history the 
earth's interior was somewhat warmer than now, and the 
surface may have been warmed more than at present by 
conduction, by lava flows, and by the fall of meteorites. 
If the earth during the Archeozoic period emitted enough 
heat to raise its surface temperature a few degrees, the 
heat would not prevent the development of low forms of 
life but might effectively prevent all glaciation. This 
does not mean that it would prevent changes of climate, 
but merely changes so extreme that their record would 
be preserved by means of ice. It will be most interesting 


to see whether future investigations in geology and 
astronomy indicate either a semi-uniform distribution of 
glacial periods throughout the past, or a more or less 
regular decrease in frequency from early times down to 
the present 

2. The Pleistocene glacial period was divided into at 
least four epochs, while in the Permian at least one 
inter-gladal epoch seems certain, and in some places the 
alternation between glacial and non-glacial beds suggests 
no less than nine. In the other glaciations the evidence is 
not yet clear. The question of periodicity is so important 
that it overthrows most glacial hypotheses. Indeed, had 
their authors known the facts as established in recent 
years, most of the hypotheses would never have been 
advanced. The carbon dioxide hypothesis is the only one 
which was framed with geologically rapid climatic alter- 
nations in mind. It certainly explains the facts of perio- 
dicity better than does any of its predecessors, but even 
so it does not account for the intimate way in which 
variations of aU degrees from those of the weather up to 
glacial epochs seem to grade into one another. 

According to our stellar hypothesis, occasional groups 
of glacial epochs would be expected to occur dose to- 
gether and to form long glacial periods. This is because 
many of the stars belong to groups or clusters in which 
the stars move in parallel paths. A good example is the 
cluster in the Hyades, where Boss has studied thirty-nine 
stars with special care.^ The stars are grouped about a 
center about 130 light years from the sun. The stars 
themselves are scattered over an area about thirty 
light years in diameter. They average about the same 
distance apart as do those near the sun, but toward the 

1 Lewis Bobs: Convergent of a Moving Cluster in Taurus; Astronom. 
Jour., Vol. 26, No. 4, 1908, pp. 31-36. 


center of the group they are somewhat closer together. 
The whole thirty-nine sweep forward in essentially 
parallel paths. Boss estimates that 800^000 years ago 
the cluster was only half as far from the sun as at pres- 
enty but probably that was as near as it has been during 
recent geological times. All of the thirty-nine stars of this 
duster, as Moulton^ puts it, ^^are much greater in light- 
giving power than the sun. The luminosities of even the 
five smallest are from five to ten times that of the sun^ 
while the largest are one hundred times greater in light- 
giving power than our own luminary. Their masses are 
probably much greater than that of the sun. * ' If the sun 
were to pass through such a duster, first one star and 
then another might come so near as to cause a profound 
disturbance in the sun's atmosphere. 

3. Another important point upon which a glacial hy- 
pothesis may come to grief is the length of the periods 
or rather of the epochs which compose the periods. 
During the last or Pleistocene gladal period the evidence 
in America and Europe indicates that the inter-glacial 
epochs varied in length and that the later ones were 
shorter than the earlier. Chamberlin and Salisbury, from 
a comparison of various authorities, estimate that the 
intervals from one glacial epoch to another form a de- 
clining series, which may be roughly expressed as fol- // 
lows: 16-8-4-2-1, where unity is the interval from the 
dimaz of the late Wisconsin, or last glacial epoch, to the 
present. Most authorities estimate the culmination of the 
late Wisconsin glaciation as twenty or thirty thousand ( 
years ago. Penck estimates the length of the last inter- ^ 
glacial period as 60,000 years and the preceding one as / 
240,000.' B. T. Chamberlin, as already stated, finds that 

sF. B. Moulton: in Introduction to Astronomy, 1016. 
B A. Penek: Die Alpen im Eiszeitalter, Leipzig, 1909. 


the consensus of opinion is that inter-glacial epochs have 
averaged five times as long as glacial epochs. The actual 
duration of the various gladations probably did not vary 
in so great a ratio as did the intervals from one glada- 
tion to another. The main point, however, is the irregu- 
larity of the various periods. 

The relation of the stellar electrical hypothesis to the 
length of glacial epochs may be estimated from column 
C, in Table 5. There we see that the distances at which 
a star might possibly disturb the sun enough to cause 
glaciation range all the way from 120 billion miles in 
the case of a small star like the sun, to 3200 billion in 
the case of Betelgeuse, while for double stars the figure 
may rise a hundred times higher. From this we can cal- 
culate how long it would take a star to pass from a point 
where its influence would first amount to a quarter of the 
assumed maximum to a similar point on the other side of 
the sun. In making these calcidations we will assume that 
the relative rate at which the star and the sun approach 
each other is about twenty-two miles per second, or 700 
million miles per year, which is the average rate of 
motion of all the known stars. According to the distances 
in Table 5 this gives a range from about 500 years up to 
about 10,000, which might rise to a million in the case of 
double stars. Of course the time might be relatively short 
if the sun and a rapidly moving star were approaching 
one another almost directly, or extremely long if the sun 
and the star were moving in almost the same direction 
and at somewhat similar rates, — a condition more 
common than the other. Here, as in so many other cases, 
the essential point is that the figures which we thus ob- 
tain seem to be of the right order of magnitude. 

4. Post-glacial climatic stages are so well known that 
in Europe they have definite names. Their sequence has 


already been discussed in Chapter XIL Fossils found in 
the peat bogs of Denmark and Scandinavia, for example, 
prove that since the final disappearance of the conti- 
nental ice cap at the close of the Wisconsin there has 
been at least one period when the climate of Europe was 
distinctly milder than now. Directly overlying the sheets 
of glacial drift laid down by the ice there is a flora corre- 
sponding to that of the present tundras. Next come re- 
mains of a forest vegetation dominated by birches and 
poplars, showing that the climate was growing a little 
warmer. Third, there follow evidences of a still more 
favorable climate in the form of a forest dominated by 
pines ; fourth, one where oak predominates ; and fifth, a 
flora similar to that of the Black Forest of Germany, 
indicating that in Scandinavia the temperature was then 
decidedly higher than today. This fifth flora has retreated 
southward once more, having been driven back to its 
present latitude by a slight recurrence of a cool stormy 
dimate.^ In central Asia evidence of post-glacial stages 
is f oimd not only in five distinct moraines but in a corre- 
sponding series of elevated strands surrounding salt 
lakes and of river terraces in non-glaciated arid regions.' 
In historic as well as prehistoric times, as we have 
already seen, there have been climatic fluctuations. For 
instance, the twelfth or thirteenth century B. C. appears 
to have been almost as mild as now, as does the seventh 
century B. C. On the other hand about 1000 B. C, at the 
time of Christ, and in the fourteenth century there were 
times of relative severity. Thus it appears that both on 

« B. D. Salisbuiy: Physical (Geography of the Pleistocene, in Outlines of 
Geologic History, by Willis and Salisbury, 1910, pp. 273-274. 

B Davis, Pumpelly, and Huntington : Explorations in Turkestan, Carnegie 
Inst, of Wash., No. 26, 1905. 

In North America the stages have been the subject of intensive studies 
on the part of Taylor, Leverett, Goldthwait, and many others. 


a large and on a small scale pulsations of climate are the 
rule. Any hypothesis of climatic changes must satisfy 
the periods of these pulsations. These conditions furnish 
a problem which makes difficulty for almost all hypothe- 
ses of climatic change. According to the present hypothe- 
siSy earth movements such as are discussed in Chapter 
XII may cooperate with two astronomical factors. One is 
the constant change in the positions of the stars, a change 
which we have already called kaleidoscopic, and the other 
is the fact that a large proportion of the stars are double 
or multiple. When one star in a group approaches the 
sun closely enough to cause a great solar disturbance, 
numerous others may approach or recede and have a 
minor effect. Thus, whenever the sun is near groups of 
stars we should expect that the earth would show many 
minor climatic pulsations and stages which might or 
might not be connected with glaciation. The historic 
pulsations shown in the curve of tree growth in CaU- 
fomia, Fig. 4, are the sort of changes that would be 
expected if movements of the stars have an effect on the 
solar atmosphere. 

Not only are fully a third of all the visible stars double, 
as we have already seen, but at least a tenth of these are 
known to be triple or multiple. In many of the double 
stars the two bodies are close together and revolve so 
rapidly that whatever periodicity they might create in 
the sun *s atmosphere would be very short In the triplets, 
however, the third star is ordinarily at least ten times 
as far from the other two as they are from each other, 
and its period of rotation sometimes runs into hundreds 
or thousands of years. An actual multiple star in the 
constellation Polaris will serve as an example. The main 
star is believed by Jeans to consist of two parts which 
are almost in contact and whirl around each other with 


extraordinary speed in four days. If this is true they 
must keep each other's atmospheres in a state of intense 
commotion. Much farther away a third star revolves 
around this pair in twelve years. At a much greater dis- 
tance a fourth star revolves around the common center 
of gravity of itself and the other three in a period which 
may be 20,000 years. Still more complicated cases prob- 
ably exist. Suppose such a system were to traverse a 
path where it would exert a perceptible influence on the 
sun for thirty or forty thousand years. The varying 
movements of its members would produce an intricate 
series of cycles which might show all sorts of major and 
minor variations in length and intensity. Thus the varied 
and irregular stages of glaciation and the pulsations of 
historic times might be accoimted for on the hypothesis 
of the proximity of the sun to a multiple star, as well as 
on that of the less pronounced approach and recession 
of a number of stars. In addition to all this, an almost 
infinitely complex series of climatic changes of long and 
short duration might arise if the sun passed through a 

5. We have seen in Chapter VIII that the contrast 
between the somewhat severe climate of the present and 
the generally mild climate of the past is one of the great 
geological problems. The glacial period is not a thing 
of the distant past. (Geologists generally recognize that 
it is still with us. Greenland and Antarctica are both 
shrouded in ice sheets in latitudes where fossil floras 
prove ^that at other periods the climate was as mild as 
in England or even New Zealand. The present glaciated 
regions, be it noted, are on the polar borders of the 
world's two most stormy oceanic areas, just where ice 
would be exi)ected to last longest according to the solar 
cyclonic hypothesis. In contrast with the semi-glacial 





conditions of the present^ the last inter-glacial epoch was 
so mild that not only men bnt elephants and hippopota- 
muses flourished in central Europe, while at earlier times 
in the middle of long eras, such as the Paleozoic and 
MesozoiCy corals, cycads, and tree ferns flourished within 
the Arctic circle. 

If the electro-stellar hypothesis of solar disturbances 
proves well founded, it may explain these peculiarities. 
Periods of mild climate would represent a return of the 
sun and the earth to their normal conditions of quiet. At 
such times the atmosphere of the sun is assimied to be 
little disturbed by sunspots, faculse, prominences, and 
other allied evidences of movements ; and the rice-g^rain 
structure is perhaps the most prominent of the solar 
markings. The earth at such times is supposed to be 
correspondingly free from cyclonic storms. Its winds are 
then largely of the purely planetary type, such as trade 
winds and westerlies. Its rainfaU also is largely planet- 
ary rather than cyclonic. It falls in places such as the 
heat equator where the air rises under the influence of 
heat, or on the windward slopes of mountains, or in re- 
gions where warm winds blow from the ocean over cold 

According to the electro-stellar hypothesis, the condi- 
tions which prevailed during hundreds of millions of 
years of mild climate mean merely that the solar system 
was then in parts of the heavens where stars — especially 
double stars — ^were rare or small, and electrical disturb- 
ances correspondingly weak. Today, on the other hand, 
the sun is fairly near a number of stars, many of which 
are large doubles. Hence it is supposed to be disturbed, 
although not so much as at the height of the last glacial 

After the preceding parts of this book had been 


written, the assistance of Dr. Schlesinger made it pos- 
sible to test the electro-stellar hypothesis by comparing 
actual astronomical dates with the dates of climatic or 
solar phenomena. In order to make this possible. Dr. 
Schlesinger and his assistants have prepared Table 6, 
giving the position, magnitude, and motions of the thirty- 
eight nearest stars, and especially the date at which each 
was nearest the sun. In column 10 where the dates are 
given, a minus sign indicates the past and a plus sign the 
future. Dr. Shapley has kindly added column 12, giving 
the absolute magnitudes of the stars, that of the sun 
being 4.8, and column 13, showing their luminosity or 
absolute radiation, that of the sun being unity. Finally, 
column 14 shows the eflfective radiation received by the 
sun from each star when the star is at a minimum dis- 
tance. Unity in this case is the effect of a star like the 
sun at a distance of one light year. 

It is well known that radiation of all kinds, including 
light, heat, and electrical emissions, varies in direct pro- 
portion to the exposed surface, that is, as the square 
of the radius of a sphere, and inversely as the square of 
the distance. From black bodies, as we have seen, the 
total radiation varies as the fourth power of the abso- 
lute temperature. It is not certain that either light or 
electrical emissions from incandescent bodies vary in 
quite this same proportion, nor is it yet certain whether 
luminous and electrical emissions vary exactly together. 
Nevertheless they are closely related. Since the light 
coming from each star is accurately measured, while no 
information is available as to electrical emissions, we 
have followed Dr. Shapley *s suggestion and used the 
luminosity of the stars as the best available measure of 
total radiation. This is presumably an approximate 
measure of electrical activity, provided some allowance 



Groombr. 34 0»»12».7 

*iy Cassiop 43 .0 

43 .9 

*jrTucanffi 1 12 .4 

T Ceti 39 .4 

dsEridani 3 15 .9 

•eEridani 28 .2 

•40(0)« Eridani 4 10 .7 

Cordoba Z. 243 5 7.7 

Wei88e592 26 .4 

•a Can. Maj. (Sinus). . . 6 40 .7 

•aCamMin. (Procyon). 7 34 .1 

•Fedorenko 1457-8 9 7 .6 

Groombr. 1618 10 5.3 

Wei88e234 14 .2 

Lalande 21185 57 .9 

Lalande 21258 11 .5 

12 .0 

Lalande 25372 13 40 .7 

*a Centauri 14 32 .8 

•^Bootes 14 46 .8 

♦Lalande 27173 51 .6 

Wei88el259 16 41 .4 

Lacaille 7194 17 11 .5 

*/3 416 12 .1 

Argel -0.17415-6 .... 37 .0 

Barnard's star ..:.... 52 .9 

•70pOphiuehi 18 .4 

*S2398 41 .7 

<r Draconis 19 32 .5 

*a AquilaB (Altair) .... 45 .9 

*61Cygni 21 2 .4 

Lacaille 8760 11 .4 

€lndi 55 .7 

*Kruger 60 22 24 .4 

Lacaille 9352 59 .4 

Lalande 46650 23 44 .0 

C. G. A. 32416 59 .5 

* Double star. 

(3) (4) (6) {6) 

+57 17 
+ 4 55 
-69 24 
-16 28 



. 3.6 






2". 89 
1 .24 
3 .01 
1 .92 

+ 3 
+ 10 

- 16 

-43 27 

- 9 48 

- 7 49 
-44 59 

- 3 42 



3 .16 

4 .08 
8 .75 
2 .22 


+ 16 
- 42 

-16 35 -1.6 AO 1 .32 — 8 

+ 5 29 0.5 P5 1 .24 - 4 

+53 7 7.9 Ma 1 .68 + 10 

+49 58 6.8 K5p 1 .45 — 30 

+20 22 9.0 ... .49 

+36 38 7.6 Mb 4 .78 - 87 

+44 2 8.5 E5 4 .52 + 65 

-57 2 12.0 ... 2 .69 

+15 26 8.5 K5 2 .30 

-60 25 0.2 G 3 .68 + 22 

JL7 + 4 

1 .96 -i- 20 



1 .19 — 4 

+68 26 90 K 1 .33 

+ 4 25 9.7 Mb 10 .30 — 80 

+ 2 31 4.3 K 1 .13 

+59 29 8.8 K 2 .31 

+69 29 4.8 G5 1 .84 +28 

+19 31 
-20 58 
+33 41 
-46 32 
-34 53 

4.6 K5p 

5.8 Ep 
8.4 ... 

5.7 K 

5.9 E5 

+ 8 36 
+38 15 
-39 15 
-57 12 
+57 12 



5 .20 

3 .53 

4 .70 


— 33 

— 64 

+ 13 

— 39 

-36 26 
+ 1 52 
-37 51 






6 .90 
1 .39 
6 .05 

+ 12 
+ 26 



(7) («) 







Ir 1 





« 3 



^ -S -i S « 


".28 " . 



- 4000 








- 47000 






• • 

. . . • 

• • • • 














+ 46000 








- 33000 
















+ 19000 








- 10000 






• • 

. . • • 







+ 65000 








+ 34000 








- 24000 








+ 69000 






• . 

• • • • 

• • • • 






+ 20000 








- 20000 






. . 

• ■ • • 

• • • • 




• . 

• • • • 

• • • • 



.76 1. 



- 28000 
















- 36000 






• • 


• • • • 




• • 


• • • m 






+ 21000 



. 0.12 



• • 


• • • • 






+ 10000 






• • 

• • • • 





.• • 

• • • • 







- 49000 
















+ 19000 








- 11000 








+ 17000 






• • 


• • • • 






- 3000 






» • • 


• • • • 






- 7000 






be made for disturbances by outside bodies such as com- 
panion stars. Hence the inclusion of column 14. 

On the basis of column 14 and of the movements and 
distances of the stars as given in the other columns Fig. 
10 has been prepared. This gives an estimate of the 
approximate electrical energy received by the sun from 
the nearest stars for 70,000 years before and after the 
present. It is based on the twenty-six stars for which 
complete data are available in Table 6. The inclusion of 
the other twelve would not alter the form of the curve, 
for even the largest of them would not change any part 
by more than about half of 1 per cent, if as much. 
Nor would the curve be visibly altered by the omission 
of all except four of the twenty-six stars actually used. 
The four that are important, and their relative lumi- 
nosity when nearest the sun, are Sirius 429,000, Altair 
153,000, Alpha Centauri 117,500, and Procyon 51,300. 
The figure for the next star is only 4970, while for this 
star combined with the other twenty-one that are imim- 
portant it is only 24,850. 

Figure 10 is not carried more than 70,000 years into 
the past or into the future because the stars near the 
sun at more remote times are not included among the 
thirty-eight having the largest known parallaxes. That 
is, they have either moved away or are not yet near 
enough to be included. Indeed, as Dr. Schlesinger 
strongly emphasizes, there may be swiftly moving, bright 
or gigantic stars which are now quite far away, but whose 
inclusion would alter Fig. 10 even within the limits of 
the 140,000 years there shown. It is almost certain, how- 
ever, that the most that these would do would be to raise, 
but not obliterate, the minima on either side of the main 

In preparing Fig. 10 it has been necessary to make 









O D 








allowance for double stars. Passing by the twenty-two 
unimportant stars, it appears that the companion of 
Sinus is eight or ten magnitudes smaller than that star, 
while the companions of Procyon and Altair are five or 
more magnitudes smaller than their bright comrades. 
This means that the luminosity of the faint components 
is at most only 1 per cent of that of their bright com- 
panions and in the case of Sirius not a hundredth of 1 
per cent. Hence their inclusion would have no visible 
effect on Fig. 10. In Alpha Centauri, on the other hand^ 
the two components are of almost the same magnitude. 
For this reason the effective radiation of that star as 
given in column 14 is doubled in Fig. 10, while for 
another reason it is raised still more. The other reason 
is that if our inferences as to the electrical effect of the 
sun on the earth and of the planets on the sun are cor- 
rect, double stars, as we have seen, must be much more 
effective electrically than single stars. By the same 
reasoning two bright stars close together must excite 
one another much more than a bright star and a very 
faint one, even if the distances in both cases are the same. 
So, too, other things being equal, a triple star must be 
more excited electrically than a double star. Hence in 
preparing Fig. 10 aU double stars receive double weight 
and each part of Alpha Centauri receives an additional 
50 per cent because both parts are bright and because 
they have a third companion to help in exciting them. 

According to the electro-stellar hypothesis. Alpha Cen- 
tauri is more important climatically than any other star 
in the heavens not only because it is triple and bright, but 
because it is the nearest of all stars, and moves fairly 
rapidly. Sirius and Procyon move slowly in respect to 
the sun, only about eleven and eight kilometers per 
second respectively, and their distances at minimum are 


fairly large, that is, 8 and 10.2 light years. Hence their 
effect on the snn changes slowly. Altair moves faster, 
about twenty-six kilometers per second, and its minimum 
distance is 6.4 light years, so that its effect changes fairly 
rapidly. Alpha Centauri moves about twenty-four kilo- 
meters per second, and its minimum distance is only 3.2 
light years. Hence its effect changes very rapidly, the 
change in its apparent Imninosity as seen from the sun 
amounting at maximum to about 30 per cent in 10,000 
years against 14 per cent for Altair, 4 for Sirius, and 2 
for Procyon. The vast majority of the stars change so 
much more slowly than even Procyon that their effect is 
almost uniform. All the stars at a distance of more than 
perhaps twenty or thirty light years may be regarded as 
sending to the sun a practically unchanging amount of 
radiation. It is the bright stars within this limit which 
are important, and their importance increases with their 
proximity, their speed of motion, and the brightness and 
number of their companions. Hence Alpha Centauri 
causes the main maximum in Fig. 10, while Sirius, Altair, 
and Procyon combine to cause a general rise of the curve 
from the past to the future. 

Let us now interpret Fig. 10 geologically. The low posi- 
tion of the curve fifty to seventy thousand years ago 
suggests a mild inter-glacial climate distinctly less severe 
than that of the present. Geologists say that such was the 
case. The curve suggests a glacial epoch culminating 
about 28,000 years ago. The best authorities put the di- 
max of the last glacial epoch between twenty-five and 
thirty thousand years ago. The curve shows an ameliora- 
tion of climate since that time, although it suggests that 
there is still considerable severity. The retreat of the ice 
from North America and Europe, and its persistence in 
Greenland and Antarctica agree with this. And the curve 


indicates that the change of climate is still persisting, a 
conclusion in harmony with the evidence as to historic 

If Alpha Centauri is really so important, the effect of 
its variations, provided it has any, ought perhaps to be 
evident in the sun. The activity of the star 's atmosphere 
presumably varies, for the orbits of the two components 
have an eccentricity of 0.51. Hence during their period 
' of revolution, 81.2 years, the distance between them 
; ranges from 1,100,000,000 to 3,300,000,000 miles. They 
were at a minimum distance in 1388, 1459, 1550, 1631, 
1713, 1794, 1875, and wiU be again in 1956. In Fig. 
11, showing sunspot variations, it is noticeable that the 
years 1794 and 1875 come just at the ends of periods of 
unusual solar activity, as indicated by the heavy hori- 
zontal line. A^similar. periods of ,ig:eat,activity^seeDas to 
:, ^ »,. I ' n^ have begun about 1914. If its duration eguals the ^verage 
. .;\of its fwA prftf^pAQggArfl^ if TiHii ftTld^ahPPi^iPJQ Back in 
the fourteenth century a period of excessive solar ac- 
tivity, which has already been described, culminated from 
' 1370 to 1385, or just before the two parts of Alpha Cen- 
tauri were at a minimum distance. Thus in three and 
perhaps four cases the sun has been unusually active 
during a time when the two parts of the star were most 
rapidly approaching each other and when their atmos- 
pheres were presumably most disturbed and their elec- 
trical emanations strongest. 

The fact that Alpha Centauri, the star which would be 
expected most strongly to influence the sun, and hence 
the earth, was nearest the sun at the climax of the last 
glacial epoch, and that today the solar atmosphere is 
most active when the star i3 presumably most disturbed 
may be of no significance. It is given for what it is worth. 
Its importance lies not in the fact that it proves any- 







o ■ 


® ® 

eo O 2 
.^ p* o 


• / 




8 a g p 8 n 


thing, but that no contradiction is found when we test 
the electro-stellar hypothesis by facts which were not 
thought of when the hypothesis was framed. A vast 
amount of astronomical work is still needed before the 
matter can be brought to any definite conclusion. In case 
the hypothesis stands firm, it may be possible to use the 
star,^ a hdp in determinig th/ex«* chronology of the 
later part of geological times. If the hypothesis is dis- 
proved, it will merely leave the question of solar varia- 
tions where it is today. It will not influence the main 
conclusions of this book as to the causes and nature of 
climatic changes. Its value lies in the fact that it calls 
attention to new lines of research. 


A LTHOUGH the problems of this book may lead far 
/% afield, they ultimately bring us back to the earth 
1 \ and to the present. Several times in the preceding 
pages there has been mention of the fact that periods of 
extreme climatic fluctuations are closely associated with 
great movements of the earth 's crust whereby mountains 
are uplifted and continents upheaved. In attempting to 
explain this association the general tendency has been 
to look largely at the past instead of the present. Hence 
it has been almost impossible to choose among three 
possibilities^ all beset with diflSculties. First, the move- 
ments of the crust may have caused the climatic fluctua- 
tions ; second, climatic changes may cause crustal move- 
ments ; and third, variations in solar activity or in some 
other outside agency may give rise to both types of terres- 
trial phenomena. 

The idea that movements of the earth's crust are the 
main cause of geological changes of climate is becoming 
increasingly untenable as the complexity and Rapidity of 
climatic changes become more clear, especially during 
post-glacial times. It implies that the earth's surface 
moves up and down with a speed and facility which 
appear to be out of the question. If volcanic activity be 
invoked the problem becomes no clearer. Even if volcanic 
dust should fill the air frequently and completely, neither 
its presence nor absence would produce such peculiar f ea- 


tures as the localization of glaciers^ the distribution of 
loesSy and the mild climate of most parts of geological 
time. Nevertheless, because of the great difficulties pre- 
sented by the other two possibilities many geologists 
still hold that directly or indirectly the greater climatic 
changes have been mainly due to movements of the 
earth 's crust and to the reaction of the crustal movements 
on the atmosphere. 

The possibility that climatic changes are in themselves 
a cause of movements of the earth's crust seems so im- 
probable that no one appears to have investigated it with 
any seriousness. Nevertheless, it is worth while to raise 
the question whether climatic extremes may cooperate 
with other agencies in setting the time when the earth's 
crust shall be deformed. 

As to the third possibility, it is perfectly logical to 
ascribe both climatic changes and crustal deformation to 
some outside agency, solar or otherwise, but hitherto 
there has been so little evidence on this point that such 
an ascription has merely begged the question. If heavenly 
bodies should approach the earth closely enough so that 
their gravitational stresses caused crustal deformation, 
all life would presumably be destroyed. As to the sun, 
there has hitherto been no conclusive evidence that it is 
related to crustal movements, although various writers 
have made suggestions along this line. In this chapter 
we shall carry these suggestions further and shall see 
that they are at least worthy of study. 

As a preliminary to this study it may be well to note 
that the coincidence between movements of the earth's 
crust and climatic changes is not so absolute as is some- 
times supposed. For example, the profound crustal 
changes at the end of the Mesozoic were not accompanied 
by widespread glaciation so far as is yet known, although 


the temperature appears to have been lowered. Nor was 
the violent volcanic and diastrophic activity in the Mio- 
cene associated with extreme climates. Indeed, there 
appears to have been little contrast from zone to zone, 
for figs, bread fruit trees, tree ferns, and other plants of 
low latitudes grew in Greenland. Nevertheless, both at 
the end of the Mesozoic and in the Miocene the climate 
may possibly have been severe for a time, although the 
record is lost. On the other hand, Kirk's recent discovery 
of glacial till in Alaska between beds carrying an un- 
doubted Middle Silurian fauna indicates glaciation at a 
time when there was Uttle movement of the crust so far 
as yet appears.^ Thus we conclude that while climatic 
changes and crustal movements usually occur together, 
they may occur separately. 

According to the solar-cyclonic hypothesis such a con- 
dition is to be expected. If the sun were especially active 
when the terrestrial conditions prohibited glaciation, 
changes of climate would still occur, but they would be 
milder than under other circumstances, and would leave 
little record in the rocks. Or there might be glaciation in 
high latitudes, such as that of southern Alaska in the 
Middle Silurian, and none elsewhere. On the other hand, 
when the sun was so inactive that no great storminess 
occurred, the upheaval of continents and the building of 
moxmtains might go on without the formation of ice 
sheets, as apparently happened at the end of the Meso- 
zoic. The lack of absolute coincidence between glaciation 
and periods of widespread emergence of the lands is 
evident even today, for there is no reason to suppose 
that the lands are notably lower or less extensive now 
than they were during the Pleistocene glaciation. In 
fact, there is much evidence that many areas have risen 

lE. Kirk: Paleozoic Glaciation in Alaska; Am. Jour. Sci., 1918, p. 511. 


since that time. Yet glaciation is now far less extensive 
than in the Pleistocene. Any attempt to explain this dif- 
ference on the basis of terrestrial changes is extremely 
difficult, for the shape and altitude of continents and 
mountains have not changed much in twenty or thirty 
thousand years. Yet the present moderately mild epochs 
like the puzzUng inter-glacial epochs of earlier times, is 
easily explicable on the assumption that the sun's atmos- 
phere mky sometimes vary in harmony witii cmstal 
activity, but does not necessarily do so at all times. 

Turning now to the main problem of how climatic 
changes may be connected with movements of the earth's 
crust, let us follow our usual method and examine what 
is happening today. Let us first inquire whether earth- 
quakes, which are one of the chief evidences that crustal 
movements are actually taking place in our own times, 
show any connection with sunspots. In order to test this, 
we have compared MUne^s Catalogue of Destructive 
Earthquakes from 1800 to 1899, with Wolf's stmspot 
numbers for the same period month by month. The earth- 
quake catalogue, as its compiler describes it, ^4s an 
attempt to give a list of earthquakes which have an- 
nounced changes of geological importance in the earth's 
crust; movements which have probably resulted in the 
creation or the extension of a line of fault, the vibrations 
accompanying which could, with proper instruments, 
have been recorded over a continent or the whole surface 
of our world. Small earthquakes have been excluded, 
while the number of large earthquakes both for ancient 
and modem times has been extended. As an illustration 
of exclusion, I may mention that between 1800 and 1808, 
which are years taken at random, I find in Mallet 's cata- 
logue 407 entries. Only thirty-seven of these, which were 
accompanied by structural damage, have been retained. 



Other catalogaes such as those of Perry and Fuchs have 
been treated similarly.'" 

If the earthquakes in such a caref iilly selected list bear 
a distinct relation to sunspots, it is at least possible and 
perhaps probable that a similar relation may exist be- 
tween solar activity and geological changes in the earth 's 
crust The result of the comparison of earthquakes and 
sxmspots is shown in Table 7. The first column gives the 
sunspot numbers ; the second, the number of months that 
had the respective spot numbers during the century from 
1800 to 1899. Column C shows the total number of earth- 
quakes during the months having any particular degree 
of spottedness ; while D, which is the significant column, 
gives the average number of destructive earthquakes per 
month under each of the six conditions of solar spotted- 







2> E 
Average Number 




number of earth- 

of earth- 

of months 


of earth' quakes in 

quakes in 


per Wolf's 

of earth- 

quakes per succeeding 





month month 


0- 15 



1.52 512 


15- 30 



1.58 310 


30- 50 



1.83 439 


50- 70 



2.06 390 





2.12 310 


over 100 



2.30 175 


s J. Milne: Catalogue of DestnictiTe Earthquakes; Bep. Brit. Asso. Adv. 
8ci., 1911. 


ness. The regularity of coltunn D is so great as to make 
it almost certain that we are here dealing with a real 
relationship. Column F, which shows the average number 
of earthquakes in the month succeeding any given condi- 
tion of the sun^ is stiU more regular except for the last 

The chance that six numbers taken at random will 
arrange themselves in any given order is one in 720. In 
other words, there is one chance in 720 that the regularity 
of column D is accidental. But column F is as regular as 
column D except for the last entry. If columns D and E 
were independent there would be one chance in about 
500,000 that the six numbers in both columns would 
fall in the same order, and one chance in 14,400 that 
five numbers in each would fall in the same order. 
But the two columns are somewhat related, for although 
the after-shocks of a great earthquake are never included 
in Milne's table, a world-shaking earthquake in one 
region during a given month probably creates conditions 
that favor similar earthquakes elsewhere during the next 
month. Hence the probability that we are dealing with a 
purely accidental arrangement in Table 7 is less than one 
in 14,400 and greater than one in 500,000. It may be one 
in 20,000 or 100,000. In any event it is so slight that there 
is high probability that directly or indirectly sunspots 
and earthquakes are somehow connected. 

In ascertaining the relation between sunspots and 
earthquakes it would be well if we could employ the strict 
method of correlation coefficients. This, however, is im- 
possible for the entire century, for the record is by no 
means homogeneous. The earlier decades are represented 
by only about one-fourth as many earthquakes as the 
later ones, a condition which is presumably due to lack of 
information. This makes no difference with the method 


employed in Table 7, since years with many and few sun- 
spots are distributed almost equally throughout the 
entire nineteenth century, but it renders the method of 
correlation coefficients inapplicable. During the period 
from 1850 onward the record is much more nearly homo- 
geneous, though not completely so. Even in these later 
decades, however, allowance must be made for the fact 
that there are more earthquakes in winter than in 
summer, the average number per month for the fifty 
years being as follows : 

Jan. 2.8 May 2.4 Sept. 2.5 

Feb. 2.4 June 2.3 Oct. 2.6 

Mar. 2.5 July 2.4 Nov. 2.7 

Apr. 2.4 Aug. 2.4 Dec. 2.8 

The correlation coefficient between the departures from 
these monthly averages and the corresponding depar- 
tures from the monthly averages of the sunspots for the 
same period, 1850-1899, are as follows : 

Sunspots and earthquakes of same month: -|-0.042, or 1.5 
times the probable error. 

Sunspots of a given month and earthquakes of that month 
and the next : -{-0.084, or 3.1 times the probable error. 

Sunspots of three consecutive months and earthquakes of 
three consecutive months allowing a lag of one month, i.e., son- 
spots of January, February, and March compared with earth- 
quakes of February, March, and April; sunspots of February, 
March, and April with earthquakes of March, April, and May, 
etc. ; +0.112, or 4.1 times the probable error. 

These coefficients are all small, but the number of in- 
dividual cases, 600 months, is so large that the probable 
error is greatly reduced, being only ±0.027 or ±0.028. 
Moreover, the nature of our data is such that even if 


there is a strong connection between solar changes and 
earth movements^ we should not expect a large correla- 
tion coefficient. In the first place, as already mentioned, 
the earthquake data are not strictly homogeneous. 
Second, an average of about two and one-half strong 
earthquakes per month is at best only a most imperfect 
indication of the actual movement of the earth's crust. 
Third, the sunspots are only a partial and imperfect 
measure of the activity of the sun's atmosphere. Fourth, 
the relation between solar activity and earthquakes is 
almost certainly indirect. In view of all these conditions, 
the regularity of Table 7 and the fact that the most im- 
portant correlation coefficient rises to more than four 
times the probable error makes it almost certain that the 
solar and terrestrial phenomena are really connected. 

We are now confronted by the perplexing question of 
how this connection can take place. Thus far only three 
possibilities present themselves, and each is open to 
objections. The chief agencies concerned in these three 
possibilities are heat, electricity, and atmospheric pres- 
sure. Heat may be dismissed very briefly. We have seen 
that the earth's surface becomes relatively cool when 
the sun is active. Theoretically even the slightest change 
in the temperature of the earth's surface must influence 
the thermal gradient far into the interior and hence cause 
a change of volume which might cause movements of the 
crust. Practically the heat of the surface ceases to be of 
appreciable importance at a depth of perhaps twenty 
feet, and even at that depth it does not act quickly enough 
to cause the relatively prompt response which seems to be 
characteristic of earthquakes in respect to the sun. 

The second possibility is based on the relationship 
between solar and terrestrial electricity. When the sun 
is active the earth's atmospheric electrical potential is 


subject to slight variations. It is well known that when 
two opposing points of an ionized solution are oppositely 
charged electrically^ a current passes through the liquid 
and sets up electrolysis whereby there is a segregation 
of materials, and a consequent change in the volume of 
the parts near the respective electrical poles. The same 
process takes place, although less freely, in a hot mass 
such as forms the interior of the earth. The question 
arises whether internal electrical currents may not pass 
between the two oppositely charged poles of the earth, 
or even between the great continental masses and the 
regions of heavier rock which underlie the oceans. Could 
this lead to electrolysis, hence to differentiation in vol- 
ume, and thus to movements of the earth's crust? Could 
the results vary in harmony with the sunt Bowie* has 
shown that numerous measurements of the strength and 
direction of the earth's gravitative pull are explicable 
only on the assumption that the upheaval of a continent 
or a mountain range is due in part not merely to pres- 
sure, or even to flowage of the rocks beneath the crust, 
but also to an actual change in volume whereby the rocks 
beneath the continent attain relatively great volume and 
those under the oceans a small volume in proportion to 
their weight. The query arises whether this change of 
volume may be related to electrical currents at some 
depth below the earth's surface. 

The objections to this hypothesis are numerous. First, 
there is little evidence of electrolytic differentiation in 
the rocks. Second, the outer part of the earth's crust is a 
very poor conductor so that it is doubtful whether even 
a high degree of electrification of the surface would have 
much effect on the interior. Third, electrolysis due to any 

s Wm. Bowie: Lecture before the Geological Club of Yale University. 
See Am. Jour. Sci., 1921. 


such mild causes as we have here postulated must be an 
extremely slow process, too slow, presumably, to have 
any appreciable result within a month or two. Other 
objections join with these three in making it seem im- 
probable that the sun^s electrical activity has any direct 
effect upon movements of the earth's crust. 

The third, or meteorological hypothesis, which makes 
barometric pressure the main intermediary between solar 
activity and earthquakes, seems at first sight almost as 
improbable as the thermal and electrical hypotheses. 
Nevertheless, it has a certain degree of observational 
support of a kind which is wholly lacking in the other two 
cases. Among the extensive writings on the periodicity of 
earthquakes one main fact stands out with great dis- 
tinctness : earthquakes vary in number according to the 
season. This fact has already been shown incidentally in 
the table of earthquake frequency by months. If allow- 
ance is made for the fact that February is a short month, 
there is a regular decrease in the frequency of severe 
earthquakes from December and January to June. Since 
most of Milne's earthquakes occurred in the northern 
hemisphere, this means that severe earthquakes occur in 
winter about 20 per cent of tener than in summer. 

The most thorough investigation of this subject seems 
to have been that of Davisson.^ His results have been 
worked over and amplified by Knott,* who has tested 
them by Schuster's exact mathematical methods. His re- 
sults are given in Table 8.' Here the northern hemisphere 

^Chas. Davisson: On the Annual and Semi-annual Seismie Perioda; 
B07. Soc. of London, Philosophical Transactional Vol. 184, 1893, 1107 fP. 

6G. G. Knott: The Physics of Earthquake Phenomena, Oxford, 1908. 

« In Table 8 the first column indicates the region ; the second, the dates ; 
and the third, the number of shocks. The fourth column gives the month in 
which the annual maximum occurs when the crude figures are smoothed by 
the use of overlapping six-monthly means. In other words, the average for 
each successive six months has been placed in the middle of the period. 





























^ •*{ *» s 

tf U H^ S 

Northern Hefmisphere 







Northern Hemisphere 





















Southeast Europe 







Vesuvius District 








Old Tromometre 







Old Tromometre 







Normal Tromometre 







Balkan, etc. 







Hungazy, etc. 










Dec. (Sept.) 




Grecian Archip. 














Switzerland, etc. 














North America 

















































Italy, North of Naples 

1 1865-1883 


Sept. (Nov.) 




East Indies 



Aug., Oct., 
or Dec.? 




Malay Archip. 







New Zealand 














Southern Hemisphere 







New Zealand 



March, May 







July, Dec 




Peru, Bolivia 








is placed first ; then come the East Indies and the Malay 
Archipelago lying close to the equator; and finally the 
southern hemisphere. In the northern hemisphere prac- 
tically all the maxima come in the winter, for the month 
of December appears in fifteen cases out of the twenty- 
five in column D, while January, February, or November 
appears in six others. It is also noticeable that in sixteen 
cases out of twenty-five the ratio of the actual to the ex- 
pected amplitude in column G is four or more, so that a 
real relationship is indicated, while the ratio falls below 
three only in Japan and Zante. The equatorial data, 
unlike those of the northern hemisphere, are indefinite, 
for in the East Indies no month shows a marked maxi- 
mum and the expected amplitude exceeds the actual am- 
plitude. Even in the Malay Archipelago, which shows a 
maximum in May, the ratio of actual to expected ampli- 
tude is only 2.6. Turning to the southern hemisphere, the 
winter months of that hemisphere are as strongly marked 
by a maximum as are the winter months of the northern 

Thus the average of January to Jnne^ iDelaaiye, ib placed between March 
and April, that for February to July between April and May, and bo on. 
Thia method eliminatee the minor fluctuations and also all periodicitiea 
having a duration of less than a year. If there were no annual periodicity 
the smoothing would result in practically the same figure for each month. 
The column marked ''Amplitude" gives the range from the highest month 
to the lowest divided by the number of earthquakes and then corrected 
according to Schuster's method which is well known to mathematicians, 
but which is so confusing to the layman that it will not be described. Next, 
in the column marked "Expected Amplitude/' we have the amplitude that 
would be expected if a series of numbers corresponding to the earthquake 
numbers and having a similar range were arranged in accidental order 
throughout the year. This also is calculated by Schuster's method in which 
the expected amplitude is equal to the square root of "pi" divided by the 
number of shocks. When the actual amplitude is four or more times the 
expected amplitude, the probability that there is a real periodicity in the 
observed phenomena becomes so great that we may regard it as practically 
certain. If there is no periodicity the two are equal. The last column gives 
the number of times by which the actual exceeds the expected ampUtude, 
and thus is a measure of the probability that earthquakes vary system- 
atically in a period of a year. 


hemisphere. July or August appears in five out of six 
cases. Here the ratio between the actual and expected 
ampUtudes is not so great as in the northern hemisphere. 
Nevertheless, it is practically four in Chile, and exceeds 
five in Peru and Bolivia, and in the data for the entire 
southern hemisphere. 

The whole relationship between earthquakes and the 
seasons in the northern and southern hemispheres is 
summed up in Fig. 12 taken from Knott The northern 
hemisphere shows a regular diminution in earthquake 
frequency from December until June, and an increase 
the rest of the year. In the southern hemisphere the 
course of events is the same so far as summer and winter 
are concerned, for August with its maximum comes in 
winter, while February with its minimum comes in 
summer. In the southern hemisphere the winter month 
of greatest seismic activity has over 100 per cent more 
earthquakes than the summer month of least activity. In 
the northern hemisphere this difference is about 80 per 
cent, but this smaller figure occurs partly because the 
northern data include certain interesting and signifi- 
cant regions like Japan and China where the usual condi- 
tions are reversed.^ If equatorial regions were included 
in Fig. 12, they would give an almost straight line. 

The connection between earthquakes and the seasons is 
so strong that almost no students of seismology question 
it, although they do not agree as to its cause. A meteoro- 
logical hypothesis seems to be the only logical explana- 
tion.* Wherever sufficient data are available, earthquakes 

7 N. F. Drake: Destructive Earthquakes in China; Bull. Seism. Soc Am., 
VoL 2, 1912, pp. 40-91, 124-133. 

s The only other explanation that seems to have any standing is the 
peyehologieal hypothesis of Montessns de Ballore as given in Les Tremble- 
ments de Terre. He attributes the apparent seasonal variation in earth- 
quakes to the fact that in winter people are within doors, and hence notice 


appear to be most numerous when climatic conditions 
cause the earth 's surface to be most heavily loaded or to 
change its load most rapidly. The main factor in the 
loading is apparently atmospheric pressure. This acts in 
two ways. First, when the continents become cold in 
winter the pressure increases. On an average the air 
at sea level presses upon the earth's surface at the rate 
of 14.7 pounds per square inch, or over a ton per square 
foot, and only a little short of thirty million tons per 
square mile. An average difference of one inch between 
the atmospheric pressure of summer and winter over ten 
million square miles of the continent of Asia, for ex- 
ample, means that the continent's load in winter is about 
ten million million tons heavier than in summer. Second, 
the changes in atmospheric pressure due to the passage 
of storms are relatively sharp and sudden. Hence they 
are probably more effective than the variations in the 
load from season to season. This is suggested by the 
rapidity with which the terrestrial response seems to 
follow the supposed solar cause of earthquakes. It is also 
suggested by the fact that violent storms are frequently 
followed by violent earthquakes. * ' Earthquake weather, * ' 
as Dr. Schlesinger suggests, is a common phrase in the 
typhoon region of Japan, China, and the East Indies. 
During tropical hurricanes a change of pressure amount- 
ing to half an inch in two hours is common. On Septem- 

movements of the earth much more than in summer when thej are out of 
doors. There is a similar difference between people's habits in high lati- 
tudes and low. Undoubtedly this does have a marked effect upon the degree 
to which minor earthquake shocks are noticed. Nevertheless, de Ballore's 
contention, as well as any other psychological explanation, is completely 
upset by two facts: First, instrumental records show the same seasonal dis- 
tribution as do records based on direct observation, and instruments cer- 
tainly are not influenced by the seasons. Second, in some places, notably 
China, as ]>rake has shown, the summer rather than the winter is very 
decidedly the time when earthquakes are most frequent 



ber 22, 1885, at False Point lighthotise on the Bay of 
Bengal, the barometer fell about an inch in six hours, 
then nearly an inch and a half in not much over two 
hours, and finally rose fully two inches inside of two 
hours. A drop of two inches in barometric pressure 
means that a load of about two million tons is removed 





J ° 




•= s a 
i < » 



i I 

Fig. 12. Seasonal distribution of earthquakes. 

{After Da/vi8son and Knott,) 
Northern Hemisphere. Southern Hemisphere. 


from each square mile of land ; the corresponding rise of 
pressure means the addition of a similar load. Such a 
storm, and to a less degree every other storm, strikes a 
blow upon the earth's surface, first by removing millions 
of tons of pressure and then by putting them on again.* 
Such storms, as we have seen, are much more frequent 
and severe when sunspots are numerous than at other 
times. Moreover, as Veeder*** long ago showed, one of the 
most noteworthy evidences of a connection between sun- 
spots and the weather is a sudden increase of pressure in 
certain widely separated high pressure areas. In most 
parts of the world winter is not only the season of 
highest pressure and of most frequent changes of 
Veeder's type, but also of severest storms. Hence a 
meteorological hypothesis would lead to the expectation 
that earthquakes would occur more frequentiy in winter 
than in summer. On the Chinese coast, however, and also 
on the oceanic side of Japan, as well as in some more 
tropical regions, the chief storms come in summer in the 
form of typhoons. These are the places where earth- 
quakes also are most abundant in summer. Thus, wher- 
ever we turn, storms and the related barometria changes 
seem to be most frequent and severe at the very times 
when earthquakes are also most frequent. 

Other meteorological factors, such as rain, snow, 
winds, and currents, probably have some effect on earth- 

• A eomparison of tropical hurricaneB with earthquakea is interesting. 
Taking all the hurricanee recorded in Augost, September, and October, from 
1880 to 1899, and the corresponding earthquakes in Milne's catalogue, the 
correlation coefficient between hurricanes and earthquakes is -|-0,236, with a 
probable error of ±0.082, the month being used as the unit. This is not a 
large correlation, yet when it is remembered that the hurricanes represent 
only a small part of the atmospheric disturbances in any given month, it 
suggests that with fuller data the correlation might be large. 

10 Ellsworth Huntington: The (Geographic Work of Br. M. A. Veeder; 
Geog. Bev., Vol. 3, March and April, 1917, Nos. 3 and 4. 


quakes through their ability to load the earth's crust. 
The coming of vegetation may also help. These agencies, 
however, appear to be of small importance compared 
with the storms. In high latitudes and in regions of 
abundant storminess most of these factors generally 
combine with barometric pressure to produce frequent 
changes in the load of the earth's crust, especially in 
winter. In low latitudes, on the other hand, there are few 
severe storms, and relatively little contrast in pressure 
and vegetation from season to season ; there is no snow ; 
and the amount of ground water changes little. With this 
goes the twofold fact that there is no marked seasonal 
distribution of earthquakes, and that except in certain 
local volcanic areas, earthquakes appear to be rare. In 
proportion to the areas concerned, for example, there is 
little evidence of earthquakes in equatorial Africa and 
South America. 

The question of the reality of the connection between 
meteorological conditions and crustal movements is so 
important that every possible test should be applied. At 
the suggestion of Professor Schlesinger we have looked 
up a very ingenious line of inquiry. During the last 
decades of the nineteenth century, a long series of ex- 
tremely accurate observations of latitude disclosed a fact 
which had previously been suspected but not demon- 
strated, namely, that the earth wabbles a little about its 
axis. The axis itself always points in the same direction, 
and since the earth slides irregularly around it the lati- 
tude of all parts of the earth keeps changing. Chandler 
has shown that the wabbling thus induced consists of 
two parts. The first is a movement in a circle with a 
radius of about fifteen feet which is described in approxi- 
mately 430 days. This so-called Eulerian movement is a 
normal gyroscopic motion like the slow gyration of a 


spinning top. This depends on purely astronomical 
causeSy and no terrestrial cause can stop it or eliminate 
it The period appears to be constant, but there are cer- 
tain puzzling irregularities. The usual amplitude of this 
movement, as Schlesinger" puts it, **is about 0".27, but 
twice in recent years it has jumped to (^^40. Such a 
change could be accounted for by supposing that the 
earth had received a severe blow or a series of milder 
blows tending in the same direction. ' ' These blows, which 
were originally suggested by Helmert are most interest- 
ing in view of our suggestion as to the blows struck by 

The second movement of the pole has a period of a 
year, and is roughly an ellipse whose longest radius is 
fourteen feet and the shortest, four feet; or, to put it 
technically, there is an annual term with a maximum 
amplitude of about 0".20. This, however, varies irregu- 
larly. The result is that the pole seems to wander over 
the earth's surface in the spiral fashion illustrated in 
Fig. 13. It was early suggested that this peculiar wan- 
dering of the pole in an annual period must be due to 
meteorological causes. Jeffreys" has investigated the 
matter exhaustively. He assumes certain reasonable 
values for the weight of air added or subtracted from 
different parts of the earth's surface according to the 
seasons. He also considers the effect of precipitation, 
vegetation, and polar ice, and of variations of tempera- 
ture and atmospheric pressure in their relation to move- 
ments of the ocean. Then he proceeds to compare all 

11 Frank Schlesinfi^er : Variations of Latitude; Their Bearing upon Our 
Knowledge of the Interior of the Earth; Proc. Am. Phil. Soc., Vol. 54, 
1915, pp. 351-358. Also Smithsonian Beport for 1916, pp. 248-254. 

13 Harold Jeif reys : Causes Contributory to the Annual Variations of 
Latitude; Monthly Notices, Boyal Astronomical Soe., Vol. 76, 1916, pp. 



these with the actual wandering of the pole from 1907 
to 1913. While it is as yet too early to say that any 
special movement of the pole was due to the specific 
meteorological conditions of any particular year, 
Jeffreys ' work makes it clear that meteorological causes, 
especially atmospheric pressure, are sufficient to cause 
the observed irregular wanderings. Slight wanderings 
may arise from various other sources such as movements 
of the rocks when geological faults occur or the rush of 
a great wave due to a submarine earthquake. So far as 


Fig. 13. Wandering of the 
pole from 1890 to 1898. 

{After Moulton.) 

known, however, all these other agencies cause insignifi- 
cant displacements compared with those arising from 
movements of the air. This fact coupled with the mathe- 
matical certainty that meteorological phenomena must 
produce some wandering of the pole, has caused most 
astronomers to accept Jeffreys ' conclusion. If we follow 
their example we are led to conclude that changes in 
atmospheric pressure and in the other meteorological 
conditions strike blows which sometimes shift the earth 


several feet from its normal position in respect to the 

If the foregoing reasoning is correct, the great and 
especially the sadden departures from the smooth 
gyroscopic circle described by the pole in the Eulerian 
motion would be expected to occur at about the same time 
as unusual earthquake activity. This brings us to an 
interesting inquiry carried out by Milne" and amplified 
by Knott.^* Taking Albrecht's representation of the 
irregular spiral-like motion of the pole, as given in Fig. 
13, they show that there is a preponderance of severe 
earthquakes at times when the direction of motion of the 
earth in reference to its axis departs from the smooth 
Eulerian curve. A summary of their results is given in 
Table 9. The table indicates that during the period from 
1892 to 1905 there were nine different times when the 
curve of Fig. 13 changed its direction or was deflected by 
less than 10° during a tenth of a year. In other words, 
during those periods it did not curve as much as it ought 
according to the Eulerian movement. At such times there 
were 179 world-shaking earthquakes, or an average of 
about 19.9 per tenth of a year. According to the other 
lines of Table 9, in thirty-two cases the deflection during 
a tenth of a year was between 10° and 25°, while in fifty- 
six cases it was from 25° to 40°. During these periods 
the curve remained close to the Eulerian path and the 
world-shaking earthquakes averaged only 8.2 and 12.9. 
Then, when the deflection was high, that is, when meteoro- 
logical conditions threw the earth far out of its Eule- 
rian course, the earthquakes were again numerous, the 
number rising to 23.4 when the deflection amounted to 
more than 55°. 

1* John Milne : British Association Beports for 1903 and 1906. 

14 G. G. Knott: The Physics of Earthquake Phenomena, Oxford, 1908. 









No. of 

No. of 

Average No. 

Deflection Deflections 


of Earthquakes 

O-IO' 9 



10-25* 32 



25-40» 56 



40-65 • 19 



over 55* 7 



In order to test this conclusion in another way we have 
followed a suggestion of Professor Schlesinger. Under 
his advice the Eulerian motion has been eliminated and 
a new series of earthquake records has been compared 
with the remaining motions of the poles which presum- 
ably arise largely from meteorological causes. For this 
purpose use has been made of the very full records of 
earthquakes published under the auspices of the Liter- 
national Seismological Commission for the years 1903 
to 1908, the only years for which they are available. 
These include every known shock of every description 
which was either recorded by seismographs or by direct 
observation in any part of the world. Each shock is given 
the same weight, no matter what its violence or how 
closely it follows another. The angle of deflection has 
been measured as Milne measured it, but since the Eule- 
rian motion is eliminated, our zero is approximately 
the normal condition which would prevail if there were 
no meteorological complications. Dividing the deflections 
into six equal groups according to the size of the angle, 
we get the result shown in Table 10. 





AvercLge angle of deflection 
{10 periods of \{q year each) 

— ICS** 
26.8 • 
40.2 • 

Average daily nwnher 
of earthquakes 



Here where some twenty thousand earthquakes are 
employed the result agrees closely with that of Milne for 
a di£Ferent series of years and for a much smaller number 
of earthquakes. So long as the path of the pole departs 
less than about 45^ from the smooth gyroscopic Eulerian 
path, the number of earthquakes is almost constant^ about 
eight and a quarter per day. When the angle becomes 
large, however, the number increases by nearly 50 per 
cent Thus the work of Milne, Knott, and Jeffreys is con- 
firmed by a new investigation. Apparently earthquakes 
and crustal movements are somehow related to sudden 
changes in the load imposed on the earth's crust by 
meteorological conditions. 

This conclusion is quite as surprising to the authors 
as to the reader — ^perhaps more so. At the beginning of 
this investigation we had no faith whatever in any im- 


portant relation between dimate and earthquakes. At its ^ 
end we are inclined to believe that the relation is close 
and important. 

It must not be supposed, however, that meteorological 
conditions are the cause of earthquakes and of move- 
ments of the earth 's crust. Even though the load that the 
climatic agencies can impose upon the earth 's crust runs 
into millions of tons per square mile, it is a trifle com- 
pared with what the crust is able to support. There is, 
however, a great difference between the cause and the 
occasion of a phenomenon. Suppose that a thick sheet of 
glass is placed under an increasing strain. If the strain 
is applied slowly enough, even so rigid a material as glass 
will ultimately bend rather than break. But suppose that 
while the tension is high the glass is tapped. A gentle 
tap may be followed by a tiny crack. A series of little 
taps may be the signal for small cracks to spread in 
every direction. A few slightly harder taps may cause 
the whole sheet to break suddenly into many pieces. Yet 
even the hardest tap may be the merest trifle compared 
with the strong force which is keeping the glass in a state 
of strain and which would ultimately bend it if given 

The earth as a whole appears to stand between steel 
and glass in rigidity. It is a matter of common observa- 
tion that rocks stand high in this respect and in the 
consequent difficulty with which they can be bent without ' 
breaking. Because of the earth's contraction the crust 
endures a constant strain, which must gradually become 
enormous. This strain is increased by the fact that sedi- 
ment is transferred from the lands to the borders of the 
sea and there forms areas of thick accumulation. From 
this has arisen the doctrine of isostasy, or of the equali- 
zation of crustal pressure. An important illustration of 


this is the oceanward and equatorial creep which has 
been described in Chapter XL There we saw that when 
the lands have once been raised to high levels or when a 
shortening of the earth's axis by contraction has in- 
creased the oceanic bulge at the equator, or when the 
reverse has happened because of tidal retardation, the 
outer part of the earth appears to creep slowly back 
toward a position of perfect isostatic adjustment. If the 
sun had no influence upon the earth, either direct or 
indirect, isostasy and other terrestrial processes might 
flex the earth's crust so gradually that changes in the 
form and height of the lands would always take place 
slowly, even from the geological point of view. Thus 
erosion would usually be able to remove the rocks as 
rapidly as they were domed above the general level. If 
this happened, mountains would be rare or unknown, and 
hence climatic contrasts would be far less marked than is 
actually the case on our earth where crustal movements 
have repeatedly been rapid enough to produce mountains. 
Nature's methods rarely allow so gradual an adjust- 
ment to the forces of isostasy. While the crust is under a 
1 strain, not only because of contraction, but because of 
changes in its load through the transference of sediments 
and the slow increase or decrease in the bulge at the 
equator, the atmosphere more or less persistently carries 
on the tapping process. The violence of that process 
varies greatly, and the variations depend largely on the 
severity of the climatic contrasts. If the main outlines of 
the cyclonic hypothesis are reUable, one of the first effects 
of a disturbance of the sim's atmosphere is increased 
storminess upon the earth. This is accompanied by in- 
creased intensity in almost every meteorological process. 
The most important effect, however, so far as the earth's 
crust is concerned would apparently be the rapid and 


intense changes of atmospheric pressure which would 
arise from the swift passage of one severe storm after 
another. Each storm would be a little tap on the tensely 
strained crust. Any single tap might be of little conse- 
quence, even though it involved a change of a billion 
tons in the pressure on an area no larger than the state 
of Rhode Island. Yet a rapid and irregular succession of 
such taps might possibly cause the crust to crack, and 
finally to collapse in response to stresses arising from 
the shrinkage of the earth. 

Another and perhaps more important effect of varia- 
tions in storminess and especially in the location of the 
stormy areas would be an acceleration of erosion in some 
places and a retardation elsewhere. A great increase in 
rainfall may almost denude the slopes of soil, while a 
diminution to the point where much of the vegetation 
dies off has a similar effect. If such changes should take 
place rapidly, great thicknesses of sediment might be 
concentrated in certain areas in a short time, thus dis- 
turbing the isostatic adjustment of the earth ^s crust. This 
might set up a state of strain which would ultimately 
have to be relieved, thus perhaps initiating profound 
crustal movements. Changes in the load of the earth *s 
crust due to erosion and the deposition of sediment, no 
matter how rapid they may be from the geological stand- 
point, are slow compared with those due to changes in 
barometric pressure. A drop of an inch in barometric 
pressure is equivalent to the removal of about five inches 
of solid rock. Even under the most favorable circum- 
stances, the removal of an average depth of five inches 
of rock or its equivalent in soil over millions of square 
miles would probably take several hundred years, while 
the removal of a similar load of air might occur in half 
a day or even a few hours. Thus the erosion and depo- 


sition due to climatic variations presumably play tiieir 
part in crustal deformation chiefly by producing crustal 
stresses, while the storms, as it were, strike sharp, sudden 

Suppose now that a prolonged period of world-wide 
mild climate, such as is described in Chapter X, should 
permit an enormous accumulation of stresses due to con- 
traction and tidal retardation. Suppose that then a 
sudden change of climate should produce a rapid shifting 
of the deep soil that had accumulated on the lands, with a 
corresponding localization and increase in strains. Sup- 
pose also that frequent and severe storms play their part, 
whether great or small, by producing an intensive tapping 
of the crust. In such a case the ultimate collapse would 
be correspondingly great, as would be evident in the 
succeeding geological epoch. The sea floor might sink 
lower, the continents might be elevated, and mountain 
ranges might be shoved up along lines of special weak- 
ness. This is the story of the geological period as known 
to historical geology. The force that causes such move- 
ments would be the pull of gravity upon the crust sur- 
rounding the earth's shrinking interior. Nevertheless 
climatic changes might occasionally set the date when the 
gravitative puU would finaUy overcome inertia, and thus 
usher in the crustal movements that close old geologic 
periods and inaugurate new ones. This, however, could 
occur only if the crust were under sufficient strain. As 
Lawson^' says in his discussion of the '' elastic rebound 
theory," the sudden shifts of the crust which seem to be 
the underlying cause of earthquakes ''can occur only 
after the accumulation of strain to a limit and . . . this 
accumulation involves a slow creep of the region affected. 

IB A. 0. LawBon: The Mobility of the Coast Ranges of California; Uniy. 
of Calif. Pub., Geology, Vol. 12, No. 7, pp. 431-473. 






In the long periods between great earthquakes the energy 
necessary for such shocks is being stored up in the rocks 
as elastic compression." 

If a period of intense storminess should occur when 
the earth as a whole was in such a state of strain, the 
sudden release of the strains might lead to terrestrial 
changes which would alter the climate still further, mak- 
ing it more extreme, and perhaps penmtting the stormi- i 
ness due to the solar disturbances to bring about gla- 
ciation. At the same time if volcanic activity should , , ^ 
increase it would add its quota to the tendency toward J f/ ^ 
glaciation. Nevertheless, it might easily happen that a 
very considerable amount of crustal movement would 
take place without causing a continental ice sheet or even 
a marked alpine ice sheet. Or again, if the strains in the 
earth ^s crust had already been largely released through 
other agencies before the stormy period began, the cli- 
mate might become severe enough to cause glaciation 
in high latitudes without leading to any very marked 
movements of the earth's crust, as apparently happened 
in the Mid-Silurian period. 


Here we must bring this study of the earth 's evolution 
to a close. Its fundamental principle has been that the 
present, if rightly understood, affords a full key to the 
past. With this as a guide we have touched on many 
hypotheses, some essential and some unessential to the 
general line of thought. The first main hypothesis is that 
the earth's present climatic variations are correlated 
with changes in the solar atmosphere. This is the key- 
note of the whole book. It is so well established, however, 


that it ranks as a theory rather than as an hypothesis. 
Next comes the hypothesis that variations in the solar 
atmosphere influence the earth 's climate chiefly by caus- 
ing variations not only in temperature but also in 
atmospheric pressure and thus in storminess, wind, and 
. rainfall. This, too, is one of the essential foundations on 
which the rest of the book is built, but though this 
cyclonic hypothesis is still a matter of discussion, it 
seems to be based on strong evidence. These two hypothe- 
ses might lead us astray were they not balanced by 
another. This other is that many climatic conditions are 
due to purely terrestrial causes, such as the form and 
altitude of the lands, the degree to which the continents 
are united, the movement of ocean currents, the activity 
of volcanoes, and the composition of the atmosphere and 
the ocean. Only by combining the solar and the terrestrial 
can the truth be perceived. Finally, the last main hypothe- 
sis of this book holds that if the climatic conditions which 
now prevail at times of solar activity were magnified 
• sufficiently and if they occurred in conjunction with cer- 
tain important terrestrial conditions of which there is 
/ good evidence, they would produce most of the notable 
\ phenomena of glacial periods. For example, they would 
/' explain such puzzling conditions as the localization and 
periodicity of glaciation, the formation of loess, and the 
\ occurrence of glaciation in low latitudes during Permian 
' and Proterozoic times. The converse of this is that if 
the conditions which now prevail at times when the sun 
is relatively inactive should be intensified, that is, if 
the sun's atmosphere should become calmer than now, 
and if the proper terrestrial conditions of topographic 
form and atmospheric composition should prevail, there 
would arise the mild climatic conditions which appear 
to have prevailed during the greater part of geological 



time. In short, there seems thus far to be no phase of 
the climate of the past which is not in harmony with an 
hypothesis which combines into a single unit the three 
main hypotheses of this book, solar, cyclonic, and terres- 

Outside the main line of thought lie several other 
hypotheses. Several of these, as well as some of the main 
hypotheses, are discussed chiefly in Earth and Sun, but 
as they are given a practical application in this book 
they deserve a place in this final sunmaary. Each of these 
secondary hypotheses is in its way important. Yet any or 
all may prove untrue without altering our main conclu- 
sions. This point cannot be too strongly emphasized, for 
there is always danger that differences of opinion as to 
minor hypotheses and even as to details may divert at- 
tention from the main point. Among the non-essential 
hypotheses is the idea that the sun's atmosphere influ- 
ences that of the earth electrically as well as thermally. 
This idea is still so new that it has only just entered the 
stage of active discussion, and naturally the weight of 
opinion is against it. Although not necessary to the main 
purpose of this book, it plays a minor role in the chapter 
dealing with the relation of the sun to other astronomical 
bodies. It also has a vital bearing on the further advance 
of the science of meteorology and the art of weather 
forecasting. Another secondary hypothesis holds that 
sunspots.are set in motion by the planets. Whether the 
effect is gravitational or more probably electrical, or 
perhaps of some other sort, does not concern us at pres- 
ent, although the weight of evidence seems to point 
toward electronic emissions. This question, like that of 
the relative parts played by heat and electricity in terres- 
trial climatic changes, can be set aside for the moment. 
What does concern us is a third hypothesis, namely, that 


if the planets really determine the periodicity of sun- 
spotSy even though not supplying the energy, the sun in 
its flight through space must have been repeatedly and 
more strongly influenced in the same way by many other 
heavenly bodies. In that case, climatic changes like those 
of the present, but sometimes greatly magnified, have pre- 
sumably arisen because of the constantly changing posi- 
tion of the solar system in respect to other parts of the 
universe. Finally, the fourth of our secondary hypotheses 
postulates that at present the date of movements of the 
earth ^s crust is often determined by the fact that storms 
and other meteorological conditions keep changing the 
load upon first one part of the earth's surface and then 
upon another. Thus stresses that have accumulated in the 
earth's isostatic shell during the preceding months are 
released. In somewhat the same way epochs of extreme 
storminess and rapid erosion in the past may possibly 
have set the date for great movements of the earth's 
crust. This hypothesis, like the other three in our secon- 
dary or non-essential group, is still so new that only the 
first steps have been taken in testing it. Yet it seems to 
deserve careful study. 

In testing all the hypotheses here discussed, primary 
and secondary alike, the first necessity is a far greater 
amount of quantitative work. In this book there has been 
a constant attempt to subject every hypothesis to the test 
of statistical facts of observation. Nevertheless, we have 
been breaking so much new ground that in many cases 
exact facts are not yet available, while in others they 
can be properly investigated only by specialists in 
physics, astronomy, or mathematics. In most cases the 
next great step is to ascertain whether the forces here 
called upon are actually great enough to produce the 
observed results. Even though they act only as a means 


of releasing the far greater forces due to the contraction 
of the earth and the sun, they need to be rigidly tested 
as to their ability to play even this minor role. Still 
another line of study that cries aloud for research is a 
fuller comparison between earthquakes on the one hand 
and meteorological conditions and the wandering of the 
poles on the other. Finally, an extremely interesting and 
hopeful quest is the determination of the positions and 
movements of additional stars and other celestial bodies, 
the faint and invisible as well as the bright, in order to 
ascertain the probable magnitude of their influence upon 
the sun and thus upon the earth at various times in the 
past and in the future. Perhaps we are even now ap- 
proaching some star that will some day give rise to a 
period of climatic stress like that of the fourteenth cen- 
tury, or possibly to a glacial epoch. Or perhaps the varia- 
tions in others of the nearer stars as well as Alpha 
Oentauri may show a close relation to changes in the sim. 
Throughout this volume we have endeavored to dis- 
cover new truth concerning the physical environment 
that has molded the evolution of all life. We have seen 
how delicate is the balance among the forces of nature, 
even though they be of the most stupendous magnitude. 
We have seen that a disturbance of this balance in one 
of the heavenly bodies may lead to profound changes in 
another far away. Yet during the billion years, more or 
less, of which we have knowledge, there appears never 
to have been a complete cataclysm involving the destruc- 
tion of all life. One star after another, if our hypothesis 
is correct, has approached the solar system closely 
enough to set the atmosphere of the sun in such commo- 
tion that great changes of climate have occurred upon 
the earth. Yet never has the solar system passed so dose 
to any other body or changed in any other way suffi- 



ciently to blot out all living things. The effect of climatic 
changes has always been to alter the environment and 
therefore to destroy part of the life of a given time, but 
with this there has invariably gone a stimulus to other 
organic types. New adaptations have occurred, new lines 
of evolutionary progress have been initiated, and the net 
result has been greater organic diversity and richness. 
Temporarily a great change of climate may seem to 
retard evolution, but only for a moment as the geologist 
counts time. Then it becomes evident that the march of 
progress has actually been more rapid than usual. Thus 
the main periods of climatic stress are the most conspicu- 
ous milestones upon the upward path toward more varied 
adaptation. The end of each such period of stress has 
found the life of the world nearer to the high mentality 
which reaches out to the utmost limits of space, of time, 
and of thought in the search for some explanation of the 
meaning of the universe. Each approach of the sun to 
other bodies, if such be the cause of the major climatic 
changes, has brought the organic world one step nearer 
to the solution of the greatest of all problems, — ^the prob- 
lem of whether there is a psychic goal beyond the mental 
goal toward which we are moving with ever accelerating 
speed. Throughout the vast eons of geological time the 
adjustment of force to force, of one body of matter to 
another, and of the physical environment to the organic 
response has been so delicate, and has tended so steadily 
toward the one main line of mental progress that there 
seems to be a purpose in it all. If the cosmic uniformity 
of climate continues to prevail and if the uniformity is 
varied by changes as stimulating as those of the past, the 
imagination can scarcely picture the wonders of the 
future. In the course of millions or even billions of years 
the development of mind, and perhaps of soul, many excel 


that of today as far as the highest known type of men- 
tality excels the primitive plasma from which all life 
appears to have arisen. 


* Indicates illustratioiiB. 

Abbot, G. G., cited, 45, 52, 237, 238, 

Abosknn, 104. 

Africa, earthquakes, 301; East, see 
East Africa; lakes, 143; North, 
see North Africa. 

African glaciation, 266. 

Air, see Atmosphere. 

Alaska, glacial till in, 287; Ice Age 
in, 221. 

Albrecht, cited, 304. 

Alexander, march of, 88 f . 

Allard, H. A., cited, 183, 184. 

Alpha Centauri, companion of, 280; 
distance from sun, 262; lumi- 
nosity, 278; speed of, 281; varia- 
tions, 282. 

Alps, loess in, 159; precipitation in, 
141; snow level in, 139. 

Altair, companion of, 280; lumi- 
nosity, 278; speed of, 281. 

Amazon forest, temperature, 17. 

Ancylus lake, 217. 

Andes, snow line, 139. 

Animals, climate and, 1. 

Antarctica, mild climate, 219; thick- 
ness of ice in, 125; winds, 135, 

Anti-cyclonic hypothesis, 135 ff. 

Appalachians, effect on ice sheet, 

Arabia, civilization in, 67. 

Aral, Sea of, 108. 

Arehean rocks, 211. 

Archeozoic, 3 f.; climate of, 267. 

Arctic Ocean, submergence, 219. 

Arctowski, H., cited, 29, 46, 244. 

Argon, increase of, 236. 

Arizona, rainfall, 89, 108; trees 
measured in, 73. 

Arrhenius, 8., cited, 36, 254. 

Arsis, of pulsation, 24. 

Asbjom Selsbane, corn of, 101. 

Asia, atmospheric pressure, 298 ; cen- 
tral, changes of climate, * 75 ; cen- 
tral, post-glacial climate, 271; 
climate, 66; glaciation in, 131; 
storminess in, 60; western, cli- 
mate in, 84 f. 

Atlantic Ocean, storminess, 57. 

Atmosphere, changes, 19 f., 229; 
composition of, 223-241; effect 
on temperature, 231. 

Atmospheric circulation, glaciation 
and, 42. 

Atmospheric electricity, solar rela- 
tions of, 56. 

Atmospheric pressure, earthquakes 
and, 298; evaporation and, 237; 
increase in, 239; redistribution of, 
49; variation, 53. 

Australia, East, mild climate, 219; 
precipitation, 144. 

Axis, earth's, 48; wabbling of, 301. 

Bacon, Sir Francis, cited, 27. 

Bacubirito, meteor at, 246. 

Baltic Sea, as lake, 217; freezing 

of, 100; ice, 26; storm-floods, 99; 

submergence, 219. 
Bardsson, Ivar, 106. 
Barkow, cited, 135. 
Barometric pressure, solar relations 

of, 56. 
BarreU, J., cited, 3, 200, 213, 234. 
BartoU, A. G., cited, 257. 



Bauer, L. A., cited, 150. 
Beaches, nnder water, 97. 
BeadneU, H. J. L., cited, 143. 
Belachistan, rainfall, 89. 
Bengal, Bay of, cyclones in, 149. 
Bengal, famine in, 104 f . 
Berlin, rainfall and temperature, 93. 
Betelgeuse, 259 f.; distance from 

sun, 262. 
Bible, climatic evidence in, 91 f . ; 

palms in, 92. 
Binary stars, 252. 
Birkeland, K., cited, 244. 
Black Earth region, loess in, 159. 
Boca, Cal., correlation coefficients, 

83, 85. 
Boltzmann, L., cited, 257. 
Bonneville, Lake, 142, 143. 
Borkum, storm-flood in, 99. 
Boss, L. cited, 268, 269. 
Botanical evidence of mild clinuites, 

167 ff. 
Boulders, on Irish coast, 119. 
Bowie, W., cited, 293. 
Bowman, I., cited, 213. 
Britain, forests, 220; level of land, 

British Isles, height of land, 111; 

temperature, 216. 
Brooks, C. E. P., cited, 115, 143, 196, 

215, 225. 
Brooks, C. F., cited, 209. 
Brown, E. W., cited, 191, 244. 
Bruckner, E., cited, 27. 
Bruckner periods, 27 f . 
Bufo, habiUt of, 202. 
Buhl stage, 216. 
BuU, Dr., cited, 100, 101. 
Butler, H. C, cited, 66, 67 ff., 70, 


California, changes of climate, * 75 ; 
correlations of rainfall, 86; meas- 
urements of sequoias in, 73, 74 ff.; 
rainfall, 108. 

Cambrian period, 4f. 

Canada, storminees, 53 f., 57; storm 
tracks in, 113. 

Cape Farewell, shore ice at, 105. 

Carbon dioxide, erosion and, 119 f.; 
from volcanoes, 23; hypothesis, 
139; importance of, 9, 11 f.; in 
Permian, 148; in atmosphere, 20, 
96, 238; in ocean, 226; nebular 
hypothesis and, 232; theory of 
glaciation, 36 ff. 

Caribbean mountains, origin of, 193. 

Carnegie Institution of Washington, 

Caspian Sea, climatic stress, 104; 
rainfall, 107 f.; rise and fall, 27; 
ruins in, 71. 

Cenozoic, 'climate, 266; fossils, 21. 

Central America, Maya ruins, 95. 

Chad, Lake, swamps of, 171. 

Chamberlin^ B. T., cited, 166, 233, 

Chamberlin, T. C, cited, 19, 36, 38, 
39, 42 f., 48, 122, 125, 152, 156, 
190, 195, 227, 269. 

Chandler, 8. C, cited, 301. 

Chinese earthquakes, periodicity of, 

Chinese, sunspot observations, 108 f. 

Chinese Turkestan, desiccation in, 

Chronology, glacial, 215. 

aarke, F. W., cited, 226, 235. 

aayton, H. H., cited, 173 f . 

Climate, effect of contraction, 
189 ff.; effect of salinity, 224; in 
history, 64-97; uniformity, 1-15; 
variability, 16-32. 

Climates, mild, causes of, 166-187; 
mild, periods of, 274. 

Climatic changes, and crustal move- 
ments, 285 ff . ; hypotheses of, 33- 
50 ; mountain-building and, * 25 ; 
post-glacial crustal movements 
and, 215-222; terrestrial causes 
of, 188-214. 

Climatic sequence, 16 f. 

Climatic stages, post-glacial, 270. 

Climatic stress, in fourteenth cen- 
tury, 98-109. 

Climatic uniformity, hypothesis of, 
65, 71 f . 

Climatic zoning, 169. 






Gloudinefls, glaeiation and, 114, 147. 

Gloadfl, as protection, 197. 

Colfax, CaL, eorrelation coefficients, 

Cologne, flood at, 99. 
Compass, variations, 150. 
Continental climate, yariations, 103. 
Continents, effect on climate, lllf. 
Contraction, effect on climate, 189 ff., 

199, 207; effect on landjB, 207; 

heat of sun and, 13 f.; irregular, 

195; of the earth, 18; of the sun, 

249; stresses caused by, 310. 
Convection, carbon dioxide, and, 239. 
Corals, in high latitudes, 21, 39, 167, 

Cordeiro, F. J. B., cited, 181, 183, 

Correlation coefficients, earthquakes 

and snnspots, 291 ; Jerusalem rain- 
fall and sequoia growth, 83 ff.; 

rainfall and tree growth, 79 ff. 
Cosmos, effect of light, 185. 
Cressey, G. B., cited, 80. 
Cretaceous, lava, 211; mountain 

ranges, 44; paleogeography, * 201; 

submergence of North America, 

CroU, J., cited, 34 ff., 176. 
CroU's hypothesis, snow line, 139. 
Crust, climate and movements of, 

63, 287, 310; movements of, 43; 

strains in, 22. 
Currents and planetary winds, 174. 
Qycads, 169. 
Cyclonic hypothesis, 97; loess and, 

163; Permian glaeiation and, 148; 

snow line, 139. 
Cyclonic storms, in glacial epochs, 

140 f.; solar electricity and, 243 

(see Storms, Storminess). 
Cyclonic vacillations, 30 f.; nature 

of, 57 ff. . 

Daily vibrations, 28 f. 
Danube, frozen, 98. 
Darwin, G. H., cited, 191. 
Daun stage, 217. 
Davis, W. M., cited, 271. 

Davisson, C, cited, 294, 295, 299. 

Day, C. P., cited, 239. 

Day, length of, 18, 191. 

Dead Sea, palms near, 92. 

Death Valley, 142. 

De Ballore, M., cited, 297, 298. 

Deep-sea circulation, rapidity, 227; 

salinity and, 176; solar activity 

and, 179. 
De Geer, S., cited, 215, 221. 
De Lapparent, A., cited, 200. 
Denmark, fossils, 271. 
"Desert pavements," 161. 
Deserts, abundant flora of, 171; and 

pulsations theory, 88 ff . ; red beds 

of, 170. 
Devonian, climate, 266; mountains, 

Dog, climate and, 1. 
Donegal County, Ireland, 220. 
Double stars, 272, 280; electrical 

effect of, 261. 
Douglass, A. E., cited, 28, 73, 74 f ., 

84, 85, 107. 
Dragon Town, destruction of, 104, 

Drake, N. F., cited, 297, 298. 
Droughts, and pulsations theory, 

87 f.; in England, 102; in India, 

104 f. 
Drumkelin Bog, Ireland, log cabin 

in, 220. 
Dust, at high levels, 240. 

Earth, crust of and the sun, 285-317; 
internal heat, 212; nature of mild 
climate, 274 ; position of axis, 181 ; 
rigidity of, 307; temperature 
gradient, 213; temperature of sur- 
face, 8. 

Earthquakes, and seasons, 294, 297; 
and Bunspots, 288 f.; and tropical 
hurricanes, 300; and wandering 
of pole, 304 f.; cause of, 307; 
compared with departures from 
Eulerian position, 306; seasonal 
distribution of, 299; seasonal 
march, 295. 

<' Earthquake weather," 298. 



East Africa^ mild climate, 219. 

East Indies, earthquakes of, 296. 

Eberswalde, tree growth at, 102 f . 

Ecliptic, obliquity of, 217. 

Electrical currents, in solar atmos- 
phere, 261. 

Electrical emissions, variation of, 

Electrical hypothesis, 150, 250 f., 
256 ff. 

Electrical phenomena, storminess 
and, 56. 

Electricity, and earthquakes, 292; 
solar, 243. 

Electro-magnetic hypothesis, 244. 

Electrons, solar, 56; variation of, 

Electro-stellar hypothesis, 274. 

Elevation, climatic changes and, 39. 

Engedi, palms in, 92. 

England, climatic stress, 101 f.; 
storminess and rainfall, 107. 

Eocene, climate, 266. 

Equinoxes, precession of, 96. 

Erosion, storminess and, 309. 

Eskimo, in Greenland, 106. 

Eulerian movement, 301, 304. 

Euphrates, 67. 

Europe, climatic stress, 98 if., 102 f . ; 
climatic table, 215; glaci&tion in, 
131; ice sheet, 121; inundations 
of rivers, 99; post-glacial climate, 
271; rainfall, 107; submergence, 
196, 200. 

Evaporation, and glaciation, 112, 
114; atmospheric pressure and, 
237; from plants, 179; impor- 
tance, 129; in trade- wind belt, 
117; rapidity of, 224. 

Evening primrose, effect of light, 

Evolution, climate and, 20; geo- 
graphical complexity and, 241; 
glaciation and, 33; of the earth, 

Faculee, cause of, 61. 
False Point Lighthouse, barometric 
pressure at, 299. 

Famine, cause of, 103; in England, 
101 f . ; in India, 104 f . ; pulsations 
theory and, 87 f . 

Faunas, and mild climates, 168 f.; 
in Permian, 152 f . 

Fennoscandian pause, 216. 

Flowering, light and, 184. 

Fog, and glaciation, 116; as pro- 
tection, 197; temperature and, 

Forests, climate and, 66. 

Form of the land, 43 ff . 

Fossil floras, and mild climates, 168 ; 
in Antarctica, 273; in Greenland, 

Fossils, 169, 230; and loess, 158; 
Archeozoic, 3f.; Cenosoic, 21; 
dating of, 153; glaeiation and, 
138; in peat bogs, 271; mild cli- 
mate, 167 ; Proterozoic, 4, 6 f . 

Fourteenth century, climatic stress 
in, 98-109. 

Fowls, F. £., cited, 45, 237, 238, 

Freeh, F., cited, 36. 

Free, E. E., cited, 142. 

Freezing, salinity and, 224. 

Fresno, rainfaU record, 82. 

''Friction variables," 247. 

Frisian Islands, storm-flood, 99. 

Fritz, H., cited, 109. 

Frogs, distribution of, 202. 

Fuchs, cited, 289. 

Galaxy, 252. 

Galveston, Tex., rainfall and tem- 
perature, 94. 

Gamer, W. W., cited, 1S3, 184. 

Gases, in air, 233. 

Geographers, and climatic changes, 
65 ff. 

Geological time table, * 5. 

Geologic oscillations, 18 f., 21 ff., 
188, 240. 

Geologists, changes in ideas of, 64 f • 

Germanic myths, 219. 

Germany, forests, 220; growth of 
trees in, 102; storms in, 102. 

Gilbert, G. K., cited, 143. 



Glacial epochs, causes of, 268; dates 
of, 216; intervals between, 264 f.; 
length of, 166 f. 

Glacial fluctuations, 24 if.; nature 
of, 57 ff. 

Glacial period, at present, 272; ice 
in, 57 f.; length of, 269; list, 265; 
temperature, 38. 

Glaciation, and loess, 155 f.; and 
movement of crust^ 287; condi- 
tions favorable for. 111; extent 
of, 124; hypotheses of, 33 ff.; in 
southern Canada, 18; localization 
of, 130 ff. ; Permian, * 145 ; solar- 

' cyclonic hypothesis of, 110-129; 
suddenness of, 138; upper limit 
of, 141. 

Goldthwait, J. W., cited, 271. 

Gondwana land, 21, 204. 

Gravitation, effect on sun, 250; pull 
of, 244. 

Great Basin, in glacial period, 126; 
salt lakes in, 142. 

Great Ice Age, see. Pleistocene. 

Great Plains, effect on ice sheet, 120. 

Greenland, climatic stress, 105 ff.; 
ice, 26; rainfall, 108; storminess, 
57; submergence, 219; vegetation, 
21, 37, 287; winds, 135, 161. 

Gregory, J. W., cited, 90 ff ., 97. 

Gschnitz stage, 216. 

Guatemala, ruins in, 95. 

Guervain, cited, 135. 

Gyroscope, earth as, 181. 

Hale, G. E., cited, 56, 62. 

Hamdulla, ci^^ 104. 

Hann, J., cited, 66. 

Hansa Union, operations of, 100. 

Harmer, P. W., cited, 115, 119. 

Heat, and earthquakes, 292; earth's 

internal, 18. 
Hedin, 8., cited, 88. 
Heim, A., cited, 190. 
Heligoland, flood in, 99. 
Helland-Hansen, B., cited, 174. 
Helmert^ P. B., cited, 302. 
Henderson, L. J., cited, 9, 10, 11, 


Henry, A. J., cited, 94, 208. 

Hercynian Mountains, 45. 

High pressure and glaciation, 115, 

Himalayas, glaciation, 144; origin 

of, 193; snow line, 139. 
Himley, cited, 104. 
Historic pulsations, 24 f.; nature of, 

57 ff. 
History, climate of, 64-97; climatic 

pulsations and, 26. 
Hobbs, W. H., cited, 115, 125, 135, 

Hot springs, temperature of, 6. 
Humphreys, W. J., cited, 2, 37 f., 

45, 46, 50, 56, 238. 
Hurricanes, in arid regions, 144; 

sunspots and, 53. 
Hyades, cluster in, 268. 

Ice, accumulations, 57 f.; advances 

of, 122; distribution of, 131; 

drift, 105. 
Ice sheets, disappearance, 128; 

limits, 120; localization, 130 ff.; 

rate of retreat, 165; thickness, 

Iceland, submergence, 219. 
lowan ice sheet, rapid retreat, 165. 
lowan loess, 158. 
India, drought, 104 f.; famine, 

104 f.; rainfaU, 108. 
Indian glaciation, 266. 
Inter-glacial epoch, Permian, 153. 
Internal heat of earth, 212. 
Ireland, Drumkelin Bog, 220; in 

glacial period, 119; level of land, 

220; storminess and rainfall, 

107; submergence, 219. 
Irish Sea, tides, 191. 
Irrigation ditches, abandoned, 97. 
Isostasy, 307 ff. 
Italy, southern, climate of, 86 f . 

Japan, earthquakes of, 296. 
Javanese mountains, origin of, 193. 
Jazartes, 108. 

Jeans, J. H., cited, 251, 252, 253, 
266, 272. 



Jeffreys, H., eited, 302, 303, 306. 

JeffreTB, J., cited, 191. 

Jericho, palms in, 92. 

Jerusalem, rainfall, 86; rainfall and 
temperature, 94; rainfall in, and 
sequoia growth, 83 ff. 

Johnson, cited, 226. 

Judea, palms in, 92. 

Jupiter, and sunspots, 243; effect of, 
253; periodicity of, 61 f.; tem- 
perature of, 258; tidal effect of, 

Jurassic, climate, 266; mountain 
ranges, 44. 

Kansas, variations of seasons, 103. 

Kara Koshun marsh. Lop Nor, 104. 

Keewatin center, 113; evaporation 
in, 129. 

Keewatin ice sheet, 121. 

Kelvin, Lord, cited, 13 f. 

Kejes, G. B., cited, 156. 

Kirk, E., cited, 287. 

Knott, C. G., cited, 294, 295, 297, 
299. 304, 306. 

Knowlton, F. H., cited, 167, 169, 
170, 212, 232. 

KSppen, W., 47, 52, 140. 

Krakatoa, glaciation and, 48; vol- 
canic hypothesis and, 45. 

Krummel, O., cited, 224, 228. 

Kullmer, G. J., cited, 113, 115, 128; 
map of storminess, * 54. 

Kungaspegel, sea routes described, 

Labor, price in England, 102. 

Labradorean center of glaciation, 

Lahontan, Lake, 142. 

Lake strands, see Strands. 

Lake Superior, lava, 211. 

Lakes, during glacial periods, 
141 f. ; in semi-arid regions, 60 ; 
of Great Basin, 126; ruins in, 97. 

Land, and water, climatic effect of, 
196 ff.; distribution of, 200; 
form of, 43 ff . ; range of tem- 
perature and, 196. 

Lavas, climatic effect of, 211. 

Lawson, A. G., cited, 310. 

Lebanon, cedars of, 83. 

Leiter, H., cited, 71. 

Leverett, F., cited, 271. 

Life, atmosphere and, 229 f . ; chemi- 
cal characteristic of, 12; effect of 
salinity, 225; of glacial period, 
127; persistence of forms, 230. 

Light, effect of atmosphere on, 236; 
effect on plants, 184 ff.; ultra- 
violet, storminess and, 56; varia- 
tion of, 275. 

Litorina sea, 218. 

Loess, date of, 156 ff.; origin of, 
155, 165. 

Lop Nor, rise of, 104; swamps, 171. 

Lows, and glacial lobes, 122; move- 
ments of, 126 if eee Storms and 

Lulan, 104. 

Lull, B. S., cited, 5, 188. 

MacDougal, D. T., cited, 171. 

McGee, W. J., cited, 156. 

Macmillan, W. D., cited, 191. 

Magdalenian period, 216. 

Magnetic fields of sunspots, 56. 

Magnetic poles, relation to storm 
tracks, 150. 

Makran, climate, 89; rainfall, 89. 

Malay Archipelago, earthquakes of, 

Mallet, B., cited, 288. 

Malta, rainfall, 86. 

Manson, M., cited, 147. 

Mayas, civilization, 26; ruins, 95. 

Mayence, flood at, 99. 

Mazelle, E., cited, 224. 

Mediterranean, climate of, 72; rain- 
fall records, 86; storminess in, 60. 

Mercury, and sunspots, 243. 

Mesozoic, climate, 266; crustal 
changes, 286; emergence of lands, 

Messier, 8; variables, 248. 

Metcalf , M. M., cited, 202. 

Meteorological factors and earth- 
quakes, 300 f. 



Meteorological hypothesis of cmstal 

movements, 294. 
Meteors, and sun's heat, 13, 246. 
Michelson, A. A., cited, 259. 
Middle Silurian, fauna in Alaska, 

Mild climates, see Climates, mild. 
Milky Way, 252. 
Mill, H. B., cited, 228. 
Milne, J., cited, 288, 290, 294, 304, 

Miocene, crustal changes, 287. 
Mississippi Basin, loess in, 159. 
Mogul emperor, and famine, 104. 
Monsoons, character of, 146; direc- 
tion of, 208; Indian famines and, 

Moulton, F. B., cited, 13, 258, 269. 
Mountain building, climatic changes 

and, * 25. 
Mountains, folding of, 190; rainfall, 

on, 208. 
Multiple stars, 252. 

Nansen, F., cited, 122, 174. 

Naplee, rainfall, 86. 

Nathorst, cited, 169. 

NebulsB, 247. 

Nebular hypothesis, 232, 267. 

Neolithic period, 218. 

Nevada, correlations of rainfall, 86. 

New England, height of land. 111. 

New Mexico, rainfall, 89. 

New Orleans, La., rainfall and tem- 
perature, 94. 

New Zealand, climate, 177; tree 
ferns, 179. 

Newcomb, S., cited, 52. 

Nile floods,' periodicity in, 245. 

Nitrogen, in atmosphere, 19. 

Niya, Chinese Turkestan, desiccation 
at, 66. 

Nocturnal cooling, changes in, 238 f . 

Norlind, A., cited, 100. 

Norsemen, route to Greenland, 26. 

Norse sagas, 219. 

North Africa, climate of, 71; Bo- 
man aqueducts in, 71. 

North America, at maximum glacia- 

tion, 122 ff. ; emergence of lands, 

193 ; glaciation in, 131 ; height of 

land. 111; interior sea in, 200; 

inundations, 196; loess in, 155; 

submergence of lands, 19, 21. 
North Atlantic Ocean, salinity, 228. 
North Sea, climatic stress, 98 ff.; 

floods around, 26, 99; rainfall, 

107; storminess, 57. 
Northern hemisphere, earthquakes 

of, 294. 
Norway, decay, 100; temperature, 

Nov®, 247. 

Oceanic circulation, carbon dioxide 
and, 39 ff. 

Oceanic climate, characteristics, 103. 

Oceanic currents, diversion, 44; in- 
fluence of land distribution, 203. 

Oceans, age of, 223; composition of, 
223-241; deepening of, 199; sa- 
linity, 19, 223; temperature, 6, 152, 
180, 226. 

Okada, T., cited, 224. 

Old Testament, temperature, 92. 

Orbital precessions, 27. 

Ordovician, climate, 266. 

Organic evolution, glacial fluctua- 
tions and, 26. 

Orion, nebulosity near, 247; stars 
near, 248. 

Orontes, 67. 

Osbom, H. F., cited, 216. 

Owens-Searles, lakes, 142. 

Oxus, 108. 

Oxygen, in atmosphere, 20, 234; in 
Permian, 152. 

Ozone, cause of, 56. 

Paleolithic, 216. 

Paleozoic, climate, 266; mountains 

in, 209. 
Palestine, change of climate, 91 f . 
Palms, climatic change and, 91 f.; 

in Ireland, 179. 
Palmyra, ruins of, 66. 
Parallaxes of stars, 276 f. 
Patrician center, 134. 



Peat-bog period, first, 218. 

Penek, A., cited, 139, 156, 157, 158, 

Pennsjlyanian, life of, 26. 
Periodicities, 245 f . 
Periodicity, of climatic phenomena, 

60 f.; of glaciation, 268; of snn- 

spots, 243. 
Permian, climate, 266; distribution 

of glaciation, 152; glaciation, 60, 

144, *145, 226; glaeiation and 

mountains, 45; life of, 26; red 

beds, 151; temperature, 146 f. 
Peny, cited, 289. 
Persia, lakes, 143; rainfaU, 89. 
Pettersson, O., cited, 98 ff., 100 f., 

103, 106, 219. 
Pirsson, L. V., cited, 3, 196. 
Planetary hypothesis, 253, 267. 
Planetary nebulae, 252. 
Planets, and sunspots, 243; effect 

of star on, 255; sunspot cycle 

and, 62 ; temperatures, 8 f • 
Plants, climate and, If.; effect of 

light, 184 ff. 
Pleion, defined, 29. 
Pleionian migrations, 29 f. 
Pleistocene, climate, 266; duration 

of, 48; glaciation, 110 ff.; ice 

sheets, *^123. 
Pluvial climate, causes of, 143; 

during glacial periods, 141. 
Po, frozen, 98. 
Polaris, 272. 

Polar wandering, hypothesis of, 48 f . 
Pole and earthquakes, 305. 
Post-glacial crustal movements and 

climatic changes, 215-222. 
Poynting, J. H., cited, 8. 
Processional hypothesis, 34 f. 
Precipitation, and glaciation, 114, 

133; during glacial period, 118; 

snow line and, 139; temperature 

and, 94. 
Procyon, companion of, 280; lumi- 
nosity, 278; speed of, 281. 
Progressive change, 241. 
Progressive desiccation, hypothesis 

of, 65 ff. 

Proterozoic, 4f.; fossils, 6f.; f^- 
ciation, 18, 144, 226, 266; lava, 
211; mountains in, 209; oceanic 
salinity, 42 f.; oxygen in air, 234; 
red beds, 151 ; temperature, 146 f . 

Pulsations, hypothesis of, 65, 72 ff. 

Pulsatory climatic changes, 72 ff. 

Pulsatory hypothesis, 272. 

Pumpelly, B., cited, 271. 

Radiation, variation of, 275. 

Radioactivity, heat of sun and, 14 f . 

Rainfall, changes in, 93 f.; glacia- 
tion and, 50; sunspots and, 53, 
* 58, 59; tree growth and, 79. 

Red beds, 151, 170. 

Rhine, flood, 99; frozen, 98. 

Rho Ophiuchi, variables, 248. 

<<Rice grains," 61. 

Richardson, O. W., cited, 256. 

Rigidity, of earth, 307. 

Roads, climate and, 66. 

Rogers, Thorwald, cited, 101. . 

Romans, aqueduct of, 71. 

Rome, history of, 87. 

Rotation, of earth, 18 f . 

Ruden, storm-flood, 99. 

Rugen, storm-flood, 99. 

Ruins, as climatic evidence, 66 ; rain- 
fall and, 60. 

Sacramento, correlation coefibients, 
82 f., 85; rainfaU, 86; rainfaU 
record, 79. 

Sagas, cited, 105 f. 

St John, G. E., cited, 236. 

Salinity, deeprsea circulation and, 
176; effect on climate, 224; in 
North Atlantic, 228; ocean tem- 
perature and, 226; of ocean, 19, 

Salisbury, R. D., cited, 111, 125, 129, 
139, 156, 206, 269, 271. 

Salt, in ocean, 223. 

San Bernardino, correlation of rain- 
faU, 85. 

Saturn, and sunspots, 243; sunspot 
cycle and, 62. 



Sajles, B. W., eited, 183. 

Sffandinavia, climatic stresB, 100 f.; 
fomilB, 271; post-glacial climate, 
271; rainfally 107; storminesSy 57, 
107; temperature, 216. 

Scandinavian center of glaciation, 

ScUesinger, F., cited, 275, 278, 298, 
301, 305. 

Schuchert, 0., cited, 3, 5, 23, * 25, 
•123, 138, '145, 168, 169, 172, 
188, 193, 196, 198, 200, * 201, 206, 
211, 230, 265. 

Schuster, A., cited, 61, 244, 294, 296. 

Sculpture, Maya, 96. 

Sea level and glaeiation, 119. 

Seasonal alternations, 28 f . 

Seasonal banding, 183 f . 

Seasonal changes, geological, 183. 

Seasons, and earthquakes, 294, 295, 
297, 299; evidences of, 169. 

Secular progression, 17 ff., 188. 

Seistan, swamps, 171. 

Sequoias, measurements of, 74 ff.; 
rainfall record, 79. 

SetcheD, W. A., cited, 1. 

Shackleton, E., cited, 125. 

Shaplej, H., cited, 246, 247, 254, 
256, 275. 

Shimek, E., cited, 157, 161. 

Shreveport, La., rainfall and tem- 
perature, 93 f. 

Shrinkage of the earth, 190. 

Siberia, and glaeiation, 132. 

Sierras, rainfall records, 82. 

Simpson, G. 0., cited, 222. 

Sirius, companion of, 280; distance 
from sun, 262; luminositj, 278; 
speed of, 281. 

Slichter, C. S., cited, 192. 

Smith, J. W., cited, 73. 

Snowfall, glaeiation and, 50, 114. 

Snowileld, climatic effects of, 115. 

Snow line, hei^t of, 138; in Andes, 
139; in Himalajras, 139. 

Solar activity, cycles of, 245; deep- 
sea circulation and, 179; ice and, 

Solar constant, 114. 

Solar-cyclonic hypothesis, 51-63, 
287; glaeiation and, 110-129. 

Solar prominences, cause of, 61. 

Solar system, 252; conservation of, 
243; proximity to stars, 63. 

Solar variations, storms and, 31. 

South America, earthquakes, 301. 

South Pole, thickness of ice at, 125. 

Southern hemisphere, earthquakes, 
296; glaeiation in, 131 f. 

Southern Pacific railroad, rainfall 
records along, 82. 

Soy beans, effect of light, 185 f . 

Space, sun's journey through, 264- 

Spiral nebuls, 251 f . ; universe of, 

Spitzbergen, submergence, 219. 

Springs, climate and, 66. 

Stars, approach to sun, 253; binary, 
252; clusters, 252, 268; effect on 
solar atmosphere, 63; dark,- 254; 
parallaxes of, 276 f.; tidal action 
of, 249. 

Stefan's Law, 257. 

Stein, M. A., cited, 78. 

Stellar approaches, probability of, 

Storm belt in arid regions, 144. 

Storm-floods, in fourteenth century, 

Storminess, and erosion, 309; and 
ice, 134; effect on glaeiation, 112; 
sunspots and, 163; temperature 
and, 94, 173. 

Storms, blows of, 300, 302; inerease^ 
60; movement of, 125 f.; move- 
ment of water and, * 175; origin 
of, 30 f.; sunspots and, 28, 53; 
see Cyclones and Lows. 

Storm tracks, during glacial period, 
117; location, 113; relation to 
magnetic poles, 150; shifting of, 

StrandiB, climate and, 66; in semi- 
arid regions, 60; of salt lakes, 142. 

Suess, E., cited, 192. 

Sun, and the earth's crust, 285-317; 
approach to star, 253; atmosphere 



of, 61, 274; atmosphere of, and 
weather, 52; cooling of, 49; con- 
traetion of, 249; disturbances of, 
172; effect of other bodies on, 242- 
263; heat, 13; journey through 
space, 264-284; Knowlton's hy- 
pothesis of, 168. 

Suncracks, 232. 

Sunspot cycles, 27 f. 

Sunspots, and earthquakes, 289; 
causes of, 61; magnetic field of, 
261; maximum of, 109; mild cli- 
mates and, 172; number, 108 f.; 
periodicity, 243; planetary hy- 
pothesis of, 253; records, 245; 
storminess and, 163; storms and, 
300; temperature of earth and, 
52, 173. 

Bunspot variations, 282. 

Swamps, as desert phenomena, 171. 

8ylt, storm-flood, 99. 

Syria, ciyilization in, 67; inscrip- 
tions in, 76; Boman aqueducts in, 

Syrian Desert, ruins in, 66. 

Talbert, cited, 213. 

Tarim Basin, red beds, 151. 

Tarim Desert, desiccation, 66. 

Tarim Biver, swamps, 171. 

Taylor, G., cited, 140, 144, 191, 271. 

Temperature, change of in Atlantic, 
174; changes in, 93; climatic 
change and, 49; critical, 9; geo- 
logical time and, 3 ; glacial period, 
38; glaciation and, 42, 132, 139; 
gradient of earth, 213; of ocean, 
180; in Norway, 177; in Permian, 
146 f.; in Proterozoic, 146 f.; 
limits, 6 ff . ; precipitation and, 94 ; 
range of, 3, 8; solar activity and, 
140; storminess and, 94, 112, 173; 
sunspots and, 28, 173; volcanic 
eruptions and, 46; zones, 172. 

Terrestial causes of climatic changes, 

Tertiary, lava, 211. 

Thames, frozen, 98. 

Thermal solar hypothesis, 49 f., 97. 

Thermo-pleion, movements of, 30. 

Thesis, of pulsations, 24. 

Thiryu, storm-flood, 99. 

Tian-Shan Mountains, irrigation in, 

Tidal action of stars, 249. 

Tidal effect, of Jupiter, 253; of 
planets, 244. 

Tidal hypothesis, 251. 

Tidal retardation, effect on land and 
sea, 191; rotation of earth and, 
18 f.; stress caused by, 310. 

Tides, cycles of, 219. 

Time, geological, see Geological 

Toads, distribution of, 202. 

Tobacco plant, effect of light, 184. 

Topography, and glaciation, 132. 

TranscsBpian Basin, red beds, 151. 

Tree ferns, in New Zealand, 179. 

Tree growth, periodicity in, 245; 
rainfall and, 79. 

Trees, in Calif omia, 219; measure- 
ment of, 73 ff. 

Triassic, climate, 266. 

Trifld Nebula, variables, 248. 

Trondheim, wheat in, 101. 

Trondhenas, com in, 101. 

Tropical cyclones, in glacial epochs, 
140f.; occurrence, 148; solar ac- 
tivity and, 113. 

Tropical hurricanes, earthquakes 
and, 300; sunspots and, 149. 

Turf an, temperature, 17. 

Turner, H. H., cited, 245. 

Tyler, J. M., cited, 216. 

Tyndall, J., cited, 36, 37. 

Typhoon region, < ' earthquake 
weather," 298. 

Typhoons, occurrence, 300. 

United States, rainf lUl and tempera- 
ture in Gulf region, 93 f . ; salt 
lakes in, 142; southwestern, cli- 
mate, 66 ; storminess, 53 f ., 60. 

Variables, 247. 
Veeder, M. A., cited, 300. 
Vegetation, theory of pulsations and, 



VennB, atmosphere of, 236. 

Vefiterbjgdy inYasion of, 106. 

Vicksburg, Miss., rainfall and tem- 
perature, 93 f . 

Volcanic activitj, climate and, 210; 
movement of the earth's crust 
and, 285; times of uplifting lands 
and, 23. 

Volcanic dust, climatic changes and, 

Volcanic hypothesis, climatic change 
and, 45 ff.; snow Une, 139. 

Volcanoes, activity of, 96. 

Volga, 108. 

Walcott, C. D., cited, 4, 230. 

Wandering of the pole, 302. 

Water, importance, 9. 

Water vapor, condensation of, 56; 
effect on life, 231; in atmos- 
phere, 19. 

Wave, effect on movement of water, 

Weather, changes of, 31 f. ; origin 
of, 174; variations, 52. 

Wells, H. G., cited, 35. 

Wendingstadt, storm-flood, 99. 

Westerlies, 21 f . 

Wheat, price in England, 102. 

White Sea, submergence, 219. 

Whitney, J. D., cited, 142. 

Wieland, G. R., cited, 169. 

Williamson, £. D., cited, 226. 

Willis, B., cited, 206. 

Winds, at ice front, 162; effect on 

currents, 174; glaciation and, 133; 

in Antarctica, 161; in glacial 

period, 119; in Greenland, 161; 

planetary system of, 174; velocity, 

Witch hazel, effect of light, 184. 
Wolf, J. B., cited, 61, 109, 288. 
Wolfer, cited, 244. 
Wright, W. B., cited, 35, 111, 119. 
Writing, among Mayas, 96. 

Yucatan, Maya civilization, 26, 107; 

rainfall, 108; ruins, 95. 
Yukon, Ice Age in, 221. 

Zante, earthquakes of, 296. 
Zonal crowding, 117. 




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