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Some Problems Of Glacial Periods

Having outlined in general terms the coming of the ice sheets and their

disappearance, we are now ready to discuss certain problems of

compelling climatic interest. The discussion will be grouped under five

heads: (I) the localization of glaciation; (II) the sudden coming of

glaciation; (III) peculiar variations in the height of the snow line and

of glaciation; (IV) lakes and other evidences of humidity in unglaciated

egions 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


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 Adirondacks, and the

White Mountains. The main ice sheet at its maximum extension reached as

far south as latitude 39 deg. in Kansas and Kentucky, and 37 deg. in Illinois.

Huge boulders were transferred more than one thousand miles from their

source in Canada. The northward extension 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 Alaska was not?

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 mountains which today receive heavy precipitation

and still contain small glaciers. Indeed, except for relatively slight

glaciation 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. Nevertheless, fairly extensive glaciation

existed much nearer the equator than is now the case.

In considering the localization of Pleistocene glaciation, 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. Aside from Antarctica, the

coldest place in the world is northeastern Siberia. There for seven

months the average temperature is below 0 deg.C., while the mean for the

whole year is below -10 deg.C. If the temperature during a glacial period

averaged 6 deg.C. 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,

although in other places, such as parts of Canada and northwestern

Europe, intense glaciation occurred where the mean temperature is much


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 Rockies 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 suffered 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 topography, 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 leeward side of mountains, the slight development of

glaciation appears to have been due to scarcity of precipitation. 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 precipitation 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 increase in

strength and waft more moisture to the western side of the Canadian

Rockies, or if similar winds increased 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 mountains 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 harmony with an increase in the activity of the

sun's atmosphere. 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 Pleistocene

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 Patrician between Hudson Bay and Lake

Superior, or the centers in Ireland, Cornwall, Wales, and the northern

Ural Mountains. As the main ice sheets advanced, however, 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


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,[46] advanced the anti-cyclonic

hypothesis of the origin of ice sheets. This hypothesis has the great

merit of focusing attention upon the fact that ice sheets are pronounced

anti-cyclonic regions of high pressure. This is proved by the strong

outblowing winds which prevail along their margins. Such winds must, of

course, be balanced by inward-moving winds at high levels. Abundant

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 inblowing 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

frequency until at an altitude of over 5000 meters they become 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 soundings.

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 surface 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 frequent on

the borders of the ice though not in its interior. Thus there is a

distinct and sufficient form of precipitation 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 averages

20 deg.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 temperature from the earth's surface upward proceeds at the

rate of 1 deg.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 deg.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 deg. and would be

able to hold 0.898 grain of water vapor per cubic foot; in other words,

it would have a relative humidity of about 18 per cent. Under no

reasonable assumption 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 topography permitted,

the ice sheets ought to move out uniformly in all directions; hence the

ice sheet ought to be as prominent to the north of the Keewatin and

Labradorean 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 glaciation and

mountain ranges seems much too close to support the anti-cyclonic

hypothesis, for the inblowing winds which on that hypothesis bring the

moisture are shown by observation to occur at heights far greater than

that of all but the loftiest ranges.

II. The sudden coming of glaciation is another problem 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 vulcanism, 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 this connection, however, it must be

remembered that solar activity may arise in various ways, as will appear

more fully later. Under certain conditions storminess may increase and

decrease slowly.

III. The height of the snow line and of glaciation furnishes 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

extended 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 presumably was lowered

almost equally in all latitudes, but a little more at the equator than

elsewhere. If glaciation were due to a temporary lessening of the

radiation received from the sun, such as is demanded by the thermal

solar hypothesis, and by the longer periods of Croll's 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.[47] 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

precipitation 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.[48] 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. Koeppen'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 latitudes 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 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

interpreted. 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 precipitation in general increased with

increased storminess. The low temperature of glacial times presumably

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-glaciated regions which are

normally dry is another of the facts which most glacial hypotheses fail

to explain satisfactorily. Beyond the ice sheets many regions appear to

have enjoyed an unusually heavy precipitation during the glacial epochs.

The evidence of this is abundant, including numerous abandoned strand

lines of salt lakes and an abundance of coarse material in deltas and

flood plains. J. D. Whitney,[49] in an interesting but neglected volume,

was one of the first to marshal the evidence of this sort. More recently

Free[50] has amplified this. According to him in the Great Basin region

of the United States sixty-two basins either contain unmistakable

evidence of lakes, or belong to one of the three great lake groups named

below. Two of these, the Lake Lahontan and the Lake Bonneville groups,

comprise twenty-nine present basins, while the third, the Owens-Searles

chain, contained at least five large lakes, the lowest being in Death

Valley. In western and central Asia a far greater series of salt lakes

is found and most of these are surrounded by strands at high levels.

Many of these are described in Explorations in Turkestan, The Pulse

of Asia, and Palestine and Its Transformation. There has been a good

deal of debate as to whether these lakes actually date from the glacial

period, as is claimed by C. E. P. Brooks, for example, or from some

other period. The evidence, however, seems to be convincing that the

lakes expanded when the ice also expanded.

According to the older glacial hypotheses the lower temperature which is

postulated as the cause of glaciation would almost certainly mean less

evaporation over the oceans and hence less precipitation during glacial

periods. To counteract this the only way in which the level of the lakes

could be raised would be because the lower temperature would cause less

evaporation from their surfaces. It seems quite impossible, however,

that the lowering of temperature, which is commonly taken to have been

not more than 10 deg.C., could counteract the lessened precipitation and

also cause an enormous expansion of most of the lakes. For example,

ancient Lake Bonneville was more than ten times as large as its modern

remnant, Great Salt Lake, and its average depth more than forty times as

great.[51] Many small lakes in the Old World expanded still more.[52]

For example, in eastern Persia many basins which now contain no lake

whatever are floored with vast deposits of lacustrine salt and are

surrounded by old lake bluffs and beaches. In northern Africa similar

conditions prevail.[53] Other, but less obvious, evidence of more

abundant rainfall in regions that are now dry is found in thick strata

of gravel, sand, and fine silt in the alluvial deposits of flood plains

and deltas.[54]

The cyclonic hypothesis supposes that increased storminess accounts for

pluvial climates in regions that are now dry just as it accounts for

glaciation in the regions of the ice sheets. Figs. 2 and 3, it will be

remembered, illustrate what happens when the sun is active. Solar

activity is accompanied by an increase in storminess in the southwestern

United States in exactly the region where elevated strands of diminished

salt lakes are most numerous. In Fig. 3, the same condition is seen in

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 probably swept far over the lands. The numerous tropical

cyclones of Australia, for example, are the chief source of

precipitation for that continent.[55] Some of the stronger cyclones

locally yield more rain in a day or two than other sources yield in a


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 glaciation in latitudes as low as 30 deg. in the

Proterozoic is correspondingly 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 altitude 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 receive 400 inches of rain per

year. The small size of the Himalayan glaciers in spite of these

favorable conditions is apparently due largely to the seasonal character

of the monsoon winds. The strong outblowing monsoons of winter cause

about half the year to be very dry with clear skies and dry winds from

the interior of Asia. In all 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 glaciation.

The inblowing southern monsoons bring all their moisture in midsummer at

just the time when it is least effective 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 glaciation in subtropical latitudes during

the Permian and Proterozoic.

(After Schuchert.)]

The assumption of a great general lowering of temperature is also not

adequate to explain glaciation in subtropical latitudes. In the first

place this would require a lowering of many degrees,--far more than in

the Pleistocene 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 appear 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 temperature 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 because 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

monsoons and thus cut off part of the supply of moisture. Evidence that

this actually happened in the cold fourteenth 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 deg. 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 moisture 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 counteract 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 deprive

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


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

exceptionally extensive and also high, especially in low latitudes. 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 preceding 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

terrestrial 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-four, and December fourteen as compared with an

average of forty-two for the months of July to September. From January

to March, when sunspot numbers averaged 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 numbers 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

frequency 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 accumulation 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 presumably joined with the extension

of the lands in producing 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

hurricanes abound. Many other circumstances would cooeperate to produce a

similar 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 difficulty 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 situation.

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 electrical 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 compass in England

pointed 24-1/2 deg. W. of N. and in 1906 17 deg. 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 associates 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 glaciation must explain not

only the glaciation of low latitudes but the lack of glaciation and the

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 summer. Hence great desert areas must have

prevailed at high latitudes. Great aridity now prevails north of the

Himalayas 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 sediment 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 produce red beds would

be still further increased.

It must not be supposed, however, that these conditions would absolutely

limit glaciation to subtropical latitudes. The presence of early Permian

glaciation in North America at Boston and in Alaska and in the Falkland

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 temperatures. This is a point which requires

further investigation. 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

contemporaneous 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 difference 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 sediments 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 well as in the various pulsations

of historic times, it seems to be necessary merely to magnify 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 magnified, 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

unquestionably 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 sun's atmosphere must always be reckoned.


[Footnote 46: W. H. Hobbs: Characteristics of Existing Glaciers, 1911.

The Role of the Glacial Anticyclones in the Air Circulation of the

Globe; Proc. Am. Phil. Soc., Vol. 54, 1915, pp. 185-225.]

[Footnote 47: R. D. Salisbury: Physiography, 1919.]

[Footnote 48: Griffith Taylor: Australian Meteorology, 1920, p. 283.]

[Footnote 49: J. D. Whitney: Climatic Changes of the Later Geological

Times, 1882.]

[Footnote 50: E. E. Free: U. S. Dept. of Agriculture, Bull. 54, 1914.

Mr. Free has prepared a summary of this Bulletin which appears in The

Solar Hypothesis, Bull. Geol. Sec. of Am., Vol. 25, pp. 559-562.]

[Footnote 51: G. K. Gilbert: Lake Bonneville; Monograph 1, U. S. Geol.


[Footnote 52: C. E. P. Brooks: Quart. Jour. Royal Meteorol. Soc., 1914,

pp. 63-66.]

[Footnote 53: H. J. L. Beadnell: A. Egyptian Oasis, London, 1909.

Ellsworth Huntington: The Libyan Oasis of Kharga; Bull. Am. Geog. Soc.,

Vol. 42, Sept., 1910, pp. 641-661.]

[Footnote 54: S. S. Visher: The Bajada of the Tucson Bolson of Southern

Arizona; Science, N. S., Mar. 23, 1913.

Ellsworth Huntington: The Basins of Eastern Persia and Seistan, in

Explorations in Turkestan.]

[Footnote 55: Griffith Taylor: Australian Meteorology, 1920, p. 189.]