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SCIENCE. 



[Vol. XVII. No. 419 



and unbroken by long periods of darkness, for, if there had been 

 a long night of four months in every year, as now, it would have 

 been fatal to all plants, and even many or most of the animals. 

 Therefore, down to nearly the close of the tertiary, the axis of the 

 earth was perpendicular to the ecliptic, and the days and nights 

 were everywhere and always equal. The temperature was kept 

 up by means of the carbonic acid and aqueous vapor in the 

 atmosphere, which formed a sort of " double blanket," and served 

 to retain the heat radiated from the sun. After a long period the 

 carbonic acid was most of it taken up from the atmosphere to 

 form our coal-beds, peat, petroleum, graphite, etc. This process 

 was followed by a thinning of the retaining cover. The heat 

 from the sun was not all retained, but was lost again by escaping 

 into stellar space. " Holes in the blanket" appeared at the poles, 

 ice and snow began to accumulate there, and eventually the gla- 

 cial epoch was inaugurated. Furthermore, he shows, that, ac- 

 according to the nebular hypothesis, the axes of the earth and 

 moon ought to have been, in their normal condition, parallel with 

 each other, and both perpendicular to the plane of the ecliptic: 

 but instead, the earth's axis is inclined 23i°, while the moon's axis 

 is practically perpendicular, it being inclined only 1° 30'. The 

 change, therefore, was with that of the earth, and was effected since 

 the moon's separation from the earth. '• In view of all these facts," 

 he says. ' ' it seems most probable that in that blank interval the gla- 

 cial epoch, or more largely between the end of the tnioceneand the 

 beginning of the Champlain, that movement occurred which gave 

 the earth seasons, unequal days and nights, and greatly enlarged 

 its limits of inhabitability. . . . When the axis became oblique, 

 more solar heat fell within the polar circle, those regions became 

 warmer, and the glacial epoch departed. If these conditions — 

 a perpendicular axis and high uplifts — could be to-day restored, 

 the atmosphere remaining as it is, the glacial epoch would re- 

 turn." 



It is the purpose of the present article to emphasize the reasons 

 for believing the direction of the earth's axis was changed about 

 the time stated above, and also to suggest the probable cause of 

 the change. In order to do this more intelligently, we must take a 

 more comprehensive view of the glacial epoch and all its attend- 

 ant phenomena than is usually found in any one or many of the 

 text-books, or papers, reports, and lectures, upon the subject. Of 

 all the geological changes and revolutions in the earth, out of 

 which has been evolved the present world of .animal and plant 

 life, the glacial epoch is certainly the most unique, and full of 

 interest to the scientific observer. What caused the glacial cold 

 has been the constant inquiry, but never answered, ever since it 

 was first proposed some forty or fifty years ago. Why should 

 corals live in security in Spitzbergen, and the red- woods of Cali- 

 fornia and the cypress-trees of the southern United States flourish 

 in the north of Greenland as late as tertiary times, where now are 

 the almost constant rigors of an Arctic winter? What caused the 

 recession of the glaciers, and why may we not have a recurrence 

 of them ? What influence, if any, did the polar ice-caps exert 

 upon tho ocean-level and ocean-currents ? Were the ice-caps 

 equal in magnitude; and, if not, what effects, if any, followed 

 such inequality, from the attraction of the sun and moon upon 

 the mass of the earth, thus abnormally distributed 2 These ques- 

 tions and kindred ones must be considered before we are prepared 

 to comprehend the full significance and consequences of the gla- 

 cial epoch. 



It seems incredible that a great ice-cap, several thousand feet 

 thick, should accumulate, and remain throughout the summer, in 

 the temperate zones, if the ecliptic were as oblique in those times 

 as now. The sun on the 21st of June would be nearly perpendic- 

 ular to the southern limit of the glacier, and would certainly exert 

 a powerful influence in preventing its formation or accumulation 

 south of the northern limits of Minnesota. On the other hand, 

 however, if we place the sun continuously perpendicular at the 

 equator, the temperate zone would be characterized by continual 

 spring weather similar to that occurring in April at the present 

 time. In such case we may readily conclude that the precipita- 

 tions of snow might be greater than that melted by the slanting 

 rays of the vernal sun, and hence might continue to increase, and 

 form a glacier of ice. 



It appears that the polar ice caps in glacial times extended as 

 far as the 40th parallel of latitude from either pole; in some places 

 the north glacier in the United States extended as far south as the 

 39th, and even to the 38th parallel; and in South America Profes- 

 sor Agassiz found evidences of glacial action as far north as the 

 87th parallel. Mr. D. Forbes informed Mr. Darwin that he had 

 seen ice-worn rocks and scratched stones at about 13,000 feet 

 height, between 13" and 30*^ south latitude. There seems also 

 some evidence of glacial action in the south-east corner of Aus- 

 tralia. In northern Asia, owing to the great extent of land sur- 

 face, it may be reasonably inferred that the southern limit of the 

 glacier was much beyond that in the United States. The moun- 

 tain-ranges in both hemispheres doubtless were covered with a 

 much L'reater accumulation of snow and ice than they are at 

 present, extending at that time to within the tropics, and perhaps 

 to the equator. But from the whole record, we may safely as- 

 sume 40° as the average limit of each, the southern being the 

 more widely extended of the two. There are many evidences 

 that these ice-sheets were not confined to the land, but that they 

 crossed gulfs, seas, and even oceans. Professor H. Carvill Lewis, 

 in a lecture published in the Journal of the Franklin Institute for 

 April, 1883, says, " It probably also filled the bed of the Atlantic 

 with ice far south of Greenland, the edge of the glacier reaching 

 from New Foundland to southern Ireland in a concaveline ; " and 

 Professor Geikie says the German Ocean was entirely filled with 

 ice. Similar evidence has been found as to the antarctic glacier. 

 We have therefore two magnificent circular polar ice-caps, each 

 of them nearly 7,000 miles in diameter, and the two covering 

 about 6 1,000, 000 square miles of the earth's surface, leaving a zone 

 of non-glaciated surface at the equator of about 139,000,000 square 

 miles; so that, at the culmination of the glacial epoch, nearly 

 one-third of the earth's surface was covered with ice. 



If, now, we could ascertain the thickness of these great glaciers, 

 we could easily estimate the amount of the earth's mass taken up 

 in the form of aqueous vapor, transferred to the polar areas, and 

 there deposited in the form of snow and ice. While admitting 

 the iocompletene.ss of the record, the weight of the evidence at 

 present is to the effect that the antarctic glacier was much 

 larger than the arctic. Upon general reasoning, this ought to 

 have been true ; for three-fourths of the land surface of the earth 

 are in the northern hemisphere, and the amount of water surface 

 in the southern and northern hemispheres respectively is in the 

 ratio of 85 to 60 In the southern hemisphere, therefore, there 

 ought to have been a greater amount of evaporation ; and, in the 

 absence of any known air-currents to carry this evaporation to 

 the north of the equator, there would necessarily be a greater 

 amount of precipitation in the southern hemisphere, and conse- 

 quently a greater accumulation of ice. That such was the fact in 

 glacial times, seems to be indicated by what is conceded to be 

 an imperfect record. Professor Dana, jn his "Manual of Ge- 

 ology," estimates the thickness of the northern glacier in America 

 to have been 11,500 feet on the watershed of Canada. Pro- 

 fessor Le Conte, in his "Elements of Geology," says, "The 

 archsean region of Canada seems to have been . . . covered 

 with a general ice mantle 3,000 to 6,000 feet thick ; " and Pro- 

 fessor James Geikie says the Scandinavian ice-sheet "could 

 hardly have been less than 6,000 or 7,000 feet thick." As Nor- 

 way extends nearly to the 72d parallel of north latitude, it is not 

 probable that the northern glacier exceeded t.vo miles in thickness 

 at its greatest height. Professor Le Conte says, " Greenland is ap- 

 parently entirely covered with an immense sheet of ice, several 

 thousand feet thick, which moves slowly seaward, and enters the 

 ocean through immense, fiords. Judging from the immense bar- 

 rier of ^icebergs found by Capt. Wilkes on its coast, the antarctic 

 continent is probably even more thickly covered with ice than 

 Greenland." Sir James Clark Ross reports having sailed for 

 several hundred miles along a perpendicular wall of ice 180 to 200 

 feet high in the antarctic continent, and found only one place 

 where the top of the ice could be seen from the mast-head of his 

 ship; and Capts. Cook and Wilkes both confirm the report of a 

 large ice-sheet in that part of the world. Professor CroU, in 

 ••Climate and Time," estimates, from all the data at hand, that 

 the thickness of the southern ice-cap at its greatest height is not 



