Human Origins

rgs-Greenland and Antarctic Circle-Geographical and Cosmic Causes-Cooling of Earth and Sun, Cold Spaces in Space, and Change in Earth's Axis, reviewed and rejected-Precession alone insufficient-Unless

r R. Ball-Former Glacial Periods-Correspondence with Croll's Theory-Length of the diffe

y geology, to something like a definite chronology of years and centuries. If astronomical causes, the dates of which admit of mathematical calculation, can be shown to have been, if not the sole or principal, yet one of the causes which must have influenced the phenomena of the glacial e

n the Antarctic region, a third in high mountain chains like those of Alaska, and of the Swiss and New Zealand Alps. In all these cases we find certain common conditions. High land in high latitudes, risi

accumulates. The growth of glaciers, follows as an inevitable consequence. The snow is converted into ice by pressure and by alternate freezing and melting, and this grows year by year, until an equilibrium is established by the ice pushing down glaciers into lower levels, where the melting is more rapid, or into the sea, where the front is floated off in icebergs, and drifts into lower latitudes. The process is the same as that by which the rainfall on high levels is drained off by rivers into the sea, so that an equilibrium is established between waste and supply. And it is to be remarked that the glacier, though composed of solid ice, behaves exactly like a river, or rather like a river of some viscous fluid like pitch or treacle. Its size depends on the magnitude of the reservoir or area drained by it; it conforms to the configuration of the valley by which it descends and the obsta

south latitude, or even lower, of a mile in length and 500 feet high above the sea; and in some instances icebergs three miles long and 1000 feet high have been recorded. As upwards of eight feet of ice must be under water for every foot that floats above it, some of these icebergs must be considerably over a mile in thickness, which implies that there must be land ice towards the south pole so thick that it is, in places, over 50

an excess of that evaporation in the solid form. This does not necessarily imply any great and permanent refrigeration of the whole earth, for although this would give the cold it would not give the ev

the causes which may have produced these postulates of a glacial period, lo

titude, a?rial and oceanic currents, and

heat, passage through colder regions of space, the position of t

the field-Lyell's theory of a different distribution and elevation of sea and land, carrying with it changes in a?rial a

all the vicissitudes of heat and cold in geological times. The latitude of Greenland and Spitzbergen is presumably the same now as it was in the Miocene period, when they were the seat of a luxuriant te

des of temperature. It is enough to say that if it were, the cooling ought to be progressive, and having once got into a glacial period we never ought to have got out of it. But we clearly have recovered from the paroxysms of cold, both of the first and second great glaciations of the recent period; and according to most geologists, from the immensely earlier one

ause it ought never to recover, but progress from bad to worse. We ought also, in this case, to have had a uniform progressive refrigeration from the beginning of geological time down to the present day, which has certainly not been the case. O

ase there ought to have been periodical variations in the earth's temperature, and hot and cold clim

e. It is hard to conceive how hot regions can exist surrounded by cold ones, or vice versa, without walls of a non-conducting medium to separate them, or that the faint heat from the fixed stars can ever have perceptibly affected the temperatu

t position has ever materially varied, and there is no known law that could cause such a variation. On the contrary, all the elaborate mathemati

miles. Any displacement therefore of the poles, which carried them away from their present position, must displace the present equator to a corresponding extent. This mass of twenty-eight miles in thickness of earth and ocean must be thrown out of the old position, and driven to establish a new equilibrium in a position many degrees north or south of it in order to affect climates materially, submerging all existing lands, and leaving, until removed by denudation, miles upon miles of solid earth in unsymmetrical belts, like the moraines of retreating glaciers, as the equator shifted into new positions. And all this must

th it the seasons, completely round, and brings them back to the old position, in about 21,000 years, and therefore if glacial periods were occasioned by them, there ought to be alternations from maximum of cold

of glacial periods. And even then the question is not of its being the sole or principal cause, but only whether it has had such a perceptible auxiliary effect on other more powerful causes, as may enable u

proceed to discuss the latest state of scientific opinion respecting it. But as Croll's theory if a real is clearly only an auxiliary cause, I wi

laciers, which descend some 4000 feet below the snow-line before the excess of ice pushing down is melted off by the summer heat unless it has been previously floated off in icebergs at a higher level. Now the mean temperature of the north of Scotland at sea-level is about 46° F., so that an elevation of 8000 or 10,000 feet would bring a great part of it well above the snow-line, and vast glaciers would inevitably accumulate, which would push down through the principal valleys almost to the sea-level; a state of things which actually exists in New Zealand, where glaciers from the Southern Alps at about this elevation descend, in some instances to within 700 feet of the sea-level, in

rth's rotation. This prevalence of easterly surface winds sweeps the waters of the Atlantic to the west, where they are intercepted by South America, turned northwards into the Gulf of Mexico, where they circle round under a tropical sun and become greatly heated, and finally run out through th

panse of ocean heated by the Gulf Stream, thus bringing us warmth and wet, while the corresponding counter-currents which blow over continental Europe and Asia from the north-east bring cold and drought. The extreme effects of this may be seen by comparing the Black Sea at Odessa, where ice often stops navigation, with the North Sea at the Lafoden islands, where the cod-fishi

ts from a Polar ocean, and seas around it frozen or covered with icebergs for nine months out of the year. We have a dome of solid ice piled up to the height of 9000 feet or upwards, and sending millions upon millions of tons of glaciers down to the sea to be floated off as icebergs. The only trace we can see here of the old great glacial period is t

ility, higher land in higher latitudes, surrounded by frozen seas, and washed by cold currents. I pass from this however,

h as Grinnell Land and Spitzbergen, could only have occurred under conditions exactly the reverse of those which produced the cold. If high land in high latitudes is the principal cause of the present glaciation of Greenland, still higher land must have been so in causing the still greater glaciation of the former period. Scandinavia, Laurentia, the British Islands, the Alps, Apennines, Rocky Mountains, Sierra Nevada, and all great mountain ranges in the northern

ows no sign of such recent marine formations as must have been deposited if it had been submerged to a sufficient depth to let the Gulf Stream escape, and the extension

, above tertiary deposits in Barbadoes and Jamaica, leading to the inference that the whole West Indian area was a deep sea in comp

much as 3000 feet above its present level during the first great glaciation; while the Champlain marine beds show that it was some hundreds of feet below the present, sea-level during part of the inter-glacial period. Scandinavia stood at least 2000 feet higher than at present during the climax of the glacial period as proved by t

ing to heights of from 20,000 to 29,000 feet above the sea, have been formed in great part during this period. Within the same period the great table-lands of Thibet and Central Asia have been uplifted, and the Asian Mediterranean Sea, of which th

m into the limited area of the Polar basin; no great continents or lofty mountain ranges to drain the return trade winds of their moisture; in short, all the conditions of a mild and moist insular climate, as opposed to those of a continental one, to understand how forests of temperate trees might flourish a

xpanses of water, have deposited their vapour in genial showers instead of in solid snow. The effect of such geographical conditions in producing both heat and cold is admirably worked out by Wallace in his Island Life, and few who read it can doubt that Lyell was right in saying that they have been the principal causes of the vicissitudes of climate. And here I may say a word to express my admiration of the innate sagacity with which Lyell, many years ago, and with comparatively few facts to work upon, sketched out the leading lines of geology, which have been confirmed by subsequent research. Details may have been corrected or added, but his main theories have stood the

Lyell to account for the glacial period, but his main law has only received confirmation-viz. that thi

the sole causes of the glacial period. The main argument is, that the phases of this period, though not exactly simultaneous over the whole world, are too nearly so to be due to mere local movements, and requi

the earth's plane of daily rotation to that of its annual revolution, necessitates seasons. Each pole must be alternately turned to and away from the sun every year. Each hemisphere, therefore, must have alternately its spring, summer, autumn, and winter. But if the earth's orbit were exactly circular, these seasons would be of equal duration, and the distance from the sun no greater in one than in

circle is completed in about 21,000 years, so that if the earth is nearest to the sun when the North Pole is turned away from it, and it is winter in the northern hemisphere, as is now the case, in 10,500 years the conditions will be reversed, and the southern hemisphere will be in perihelion, or nearest the sun, when it

utions come round far too rapidly, and it is impossible to suppose that there have been glacial and genial periods alternating every 10,500 years, with all the inevitable changes of seas and lands, and of fauna and flora, accompanying each alternation throughout the

rom the formula of the great astronomer Leverrier, and found that going back for the last 260,000 years there had been two maxima of high eccentricity, one 100,000 years, and the other, and more intense, 210,000 years ago, with corresponding minima of low eccentricity between, which corresponded remarkably well with the refrigeration commencing in the Pliocene, culminating towards its close or in the early Quaternary, subsiding into a long inter-glacial period, r

d assumed the number of units of heat received from the sun, in a hemisphere of the earth, as equal in summer and winter. But in reality, of 100 such units, 63 are received in summer and only 37 in winter. As the maximum of eccentricity which is possible would produce an inequality between summer and winter of 33 days, they had the following possible conditions in a hemisphere-summer 199 days and winter 166 days, or summer 166 days and winter 199 days. In each case it must be borne in mind that 63 heat units arrived in summer and 37 in winter. If the summer were a long one and the

es to assigning, this as the sole or principal cause of Ice Ages, as to precession alone, viz. that periods of high eccentricity occur too frequently to allow us to suppose that every such period in the past has had its corresponding glacial period. There was a maximum phase of eccentricity 700,000 years ago, even higher than that

auses, they would not supply anything like the number of glacial periods required by Croll's theory. Croll attempts to meet this by the extensive denudation which has repeatedly carried away such large portions of land surface; but this scarcely explains the absence of the boulders of hard rocks, which accompany every moraine and iceberg; and still less the continuance of the same fauna and flora throughout whole geological periods with little o

s favour genial climates; but whether it has not a co-operating effect, when these conditions are such as to produce glaciation. It seems difficult to suppose that such contrasts of conditions as are pointed out by Si

six astronomical phases, corresponding to these six geological phases. Geology shows that each of its six phases involves several minor alternations of hot and cold; Croll shows that this must have been the case owing to the effects of the shorter cycles of precession, occurring during the long cycles of variations in eccentricity. Geology tells us th

allowed for the immense amount of geological work in the way of denudation and deposition, elevation and depression, and changes of fauna and flora which have occurred since the commencement of the great refrigeration in the late Pliocene. In fact the on

eriod, and was already widely spread and in considerable numbers in the early glacial, 250,000 years may be taken as an approximation to the minimum duration of the existence of the human race on the earth. To this must be added an indefinitely long period beyond, unless we are prepared to disprove the apparently excessively strong evidence for its existence in the Pliocene and even in the Miocene periods; evidence which has been rapidly accumulat