February 13, 1891.] 



SCIENCE. 



95 



less than twelve miles. It is not probable that the antarctic glacier 

 was much, if any, higher than this in glacial times ; for it will be 

 readily understood, that, after the glaciation bad proceeded so far 

 as to place the south pole in the midst of a vast ice plain, the in- 

 coming clouds from the surrounding oceans would deposit most 

 of their moisture before reaching the centre, and the glacier 

 would be built up at or near its circumference. Hence we 

 should expect to find the glacier, instead of thinning gradually 

 from twelve miles at the centre to nothing at its outward edges, 

 would ijresent more the appearance of a great section of a hollow 

 sphere of nearly uniform thickness, laid over the earth at the 

 pole. 



Further confirmation of this view is found in the fact that the 

 southern hemisphere has a cooler mean annual temperature than 

 the northern. Mr. Croll sajs this is due to the constant trans- 

 ferrence of heat to the north by means of ocean- currents, nearly 

 I all the great currents originating south of the equator ; while Sir 

 Charles Lyell thinks the true cause lies in the fact of the smaller 

 extent of land surface in the south. It is also true that from 

 March 20 to Sept. 23 — the duration of the sun's northern decli- 

 nation — there are 186 days, while from the autumnal to the 

 vernal equinox there are only 179 days : the northern summer is 

 therefore seven days longer than the southern summer, and the 

 southern winter is that much longer than the northern. If this 

 inequality in the length of the summer and winter in the two 

 hemispheres had its origin during the glacial epoch, it would at 

 least have the effect of melting the ice in the north more rapidly 

 than in the southern hemisphere ; and, if it existed before glacial 

 times, the effect would have been to accelerate the growth of 

 the southern ice-caj) more rapidly than that of the northern. 



At the culmination of the glacial epoch, ther^efore, we ma^ as- 

 sume that the northern glacier was of an average thickness of 1 

 mile, and in extent about 25,000,000 square miles, making 35,- 

 000,000 cubic miles of ice; that the area covered by the southern 

 glacier was about 80,000,000 square miles, and 5 miles of average 

 thickness, making 150,000,000 cubic miles of ice; and the two ex- 

 tending over more than^ one-fourth of the earth's surface, and 

 aggregating 175,000,000 cubic miles of ice. These two gigantic 

 " fossils " would be equal in size to about one-thirtieth part of 

 the bulk of the moon, and would represent an amount of evapo- 

 ration from the water surface of the earth sufficient to lower the 

 sea-level more than 5,000 feet, or about one mile. 



Now, I submit that the attraction of the sun and moon upon 

 this mass of ice would, if continued for a long time, be sufHcient 

 to effect some change in the direction of the earth's axis. Just 

 how much that change would be, I have not determined ; but 

 that there would be some change seems to be evident from the 

 bare statement of the proposition. When we consider that this 

 matter has been removed to the poles from the equatorial regions, 

 the inequality of distribution of the earth's mass would be 

 greatly augmented. The action and re-action of the ' sun and 

 moon and the planets on the protuberant mass of matter about 

 the equator produce what is called " nutation," and the procession 

 of the equinoxes. Now, this mass being equally distributed 

 around the earth like a ring at the equator, only the nutation, or 

 nodding, of the axis is produced. But in the case of the antarctic 

 ice-caps the result of the attraction would be somewhat different; 

 for, this being largely at one side or at the pole, and the mean at- 

 traction of the moon being in the plane of the ecliptic, its ten- 

 dency would be to draw the mass towards the ecliptic — so far, 

 at least, until an equihbrium should be found. 



That the relative magnitudes of the two polar ice-sheets should 

 always remain the same, would hardly be presumed. The sinking 

 of the ice to the bottom of the Northern Atlantic would necessarily 

 cut off the Gulf Stream, and prevent its further progress north- 

 ward, if it existed in preglacial times. Even if the ice extended 

 only a few hundred feet below the surface, it would materially 

 interfere with that current, since it is a broad shallow stream, 

 flowing upon the top of the ocean. Similar conditions in the 

 southern ocean might have aided the causes already named in 

 effecting a change or changes in the relative sizes of the two great 

 glaciers. During such changes, therefore, if any existed, oscil- 

 lations of the earth's axis may have occurred before it became 



fixed as at present. We should therefore expect to find pauses in 

 the recession, and perhaps a re-advance, of the northern glacier; 

 and such we do actually find from an examination of the great 

 Kettle Moraine in the northern United States, and of the rein- 

 deer epoch in Europe. 



As already stated, the ocean-level would be very materially 

 lovs'ered. Thus we can account, in part at least, for the land 

 elevations in high latitudes, to which all geologists resort for a 

 partial explanation of glacial phenomena. True, this lowering of 

 the level would be co-extensive with the entire ocean surface; and 

 the old shore-lines would be found, if discovered at all, below the 

 present water-level. But, as Professor Dana says, " elevations 

 of land do not leave accessible records like subsidences." One of 

 the strongest evidences of land elevation is the existence of nu- 

 merous extensive fiords, which Professor Dana says are " valleys of 

 erosion," and which Professor Le Conte calls "half-submerged 

 glacial valleys." But, as the ice did not exist at sea-level in low 

 latitudes, these fiords are not found there as fossil remains to 

 mark the degree of elevation. But we know that England was 

 united to the continent of Europe by dry land, that the Mediter- 

 ranean sea was an interlocked fresh-water lake, that the delta of 

 the Mississippi was at least 400 feet higher than it is at present, 

 and that many of the islands of the Pacific Ocean were at a higher 

 level. Professor Winchell, in his "Pre- Adamites,'" says that 

 probably the now sunken continent of Lemuria, in the Indian 

 Ocean, was dry land during the glacial period, as were also some 

 of the Malay Islands and others. Professor Le Conte says, " The 

 boldness of the whole Pacific coast, especially in high latitudes, 

 indicates a previous more elevated condition of the land surface 

 [during the quaternary] than now exists; " and Mr. Darwin thinks 

 that " at this period of extreme cold the climate under the equator 

 at the level of the sea was about the same with that now felt 

 there at the height of six or seven thousand feet." 



Moreover, if this inequality in the amount of the accumulation 

 at the two poles existed as intimated, it would be sufficient to 

 remove the centre of gravity of the earth a little to the southward 

 of its former po.'ition. This would be followed by a greater flow 

 of water from the north polar i-egions ; and here we would have 

 another cause of land elevation in high northern latitudes, since 

 lowering the water-level is equivalent to an elevation of the land. 

 While there may have been local elevations and subsidences of 

 the land surface in high latitudes during the glacial and Cham- 

 plain periods, there seems to be strong reason for believing that 

 the growth and decay of the two great ice-barriers added materi- 

 ally to such changes of level by alternately lowering and elevat- 

 ing the general ocean surface. This lowering of the sea-level 

 might be taken into account in considering the question of the 

 geographical distribution of plants and animals ; but it is not my 

 design to pursue that branch of the subject here. 



The suggestion here made, that the large accumulation of the 

 earth's mass at the south pole was one of the contributive causes 

 of the change in the direction of the earth's axis, is but a corol- 

 lary to Dr. Warring's statement, that "between the end of the 

 miocene and the beginning of the Champlain, that movement 

 occurred which gave the earth seasons, unequal days and nights, 

 and greatly enlarged its limits of inhabitability." 



T. A. Bereman. 



Mount Pleasant, lo., Feb. 5. 



BOOK-REVIEWS. 



HegeVs Logic : a Critical Exposition. By William T. Harris. 

 Chicago, S. C. Griggs & Co. 16°. $1.50. 

 What Hegel calls logic is what other folks call metaphysic; 

 and Mr. Harris has here undertaken to tell us what, as he under- 

 stands it, Hegel's metaphysic is. We say " as he understands it ; " 

 for it is notorious that Hegel's disciples have not been agreed as 

 to what his philosophy really is, some giving it a pantheistic or 

 atheistic interpretation, while others, like Mr. Harris, think it a 

 perfect philosophical basis for Christianity. This disagreement is 

 partly due to the obscurity of Hegel's style, which makes it im- 

 possible m some cases to understand him, and his disciples have 

 in this respect followed the bad example of their master. The 



