SCIENCE. 



625 



in the rich forests that seemed to have flourished close to 

 the walls of ice" (p. 119). In Europe, and perhaps in 

 Asia and America he was a contemporary of man. In 

 Asia, he dwelt in vast numbers on the plains of Siberia. 

 " When he abounded there, the climate was * * * as cold 

 as it is at present. The rivers in that country have their 

 sources farther to the south than their main streams, so 

 that the springtime sends down a torrrent of water before 

 the more northern channels are released from their wintry 

 bonds ; the elephants seem to have herded together 

 along these streams for winter quarters, *** and to have 

 been swept away to the north by the inundations. These 

 freshets carried their bodies to latitudes where the cold 

 was so great that they were frozen in the mud that wrap- 

 ped them round and covered them to such a depth that 

 the brief summer-times never melted their icy casing " 

 (pp. 119-20)'. Some of these bodies remained undecom- 

 posed up to the time of their discovery in recent years; 

 and their tusks yet occur in such numbers as to be of com- 

 mercial importance. The low temperature under which 

 the mammoth existed is attested not only by his hairy 

 covering, but by the coniferous vegetation upon which he, 

 with his congeners, appears to have subsisted. Whether 

 his final extinction was accomplished by human agency 

 is a question ; but it is little less than certain that he en- 

 tered the glacial era with man, was hunted in Europe, 

 Asia, and America by paleolithic savages, and survived 

 until the amelioration of the glacial climate. 



XI. Relation of glaciation to the history of man. — The 

 evidence concerning man's relation to the glacial period 

 is divisible into two categories : — (1) that which connects 

 him with ihe closing stages of that epoch ; ( 2) that which 

 establishes his existence previous to the advent of the ice. 

 The evidence belonging to the first category is overwhelm- 

 ing in quantity ; it mainly consists in the finding of human 

 bones and products of art associated with the remains ol 

 glacial animals or imbedded in later glacial deposits. 

 That belonging to the second class is much more meagre, 

 and has been obtained satisfactorily in only three locali- 

 ties, viz, ; central France, California, and New Jersey. 

 In the first of these localities a human cranium was dis- 

 covered in volcanic tufa beneath a sheet of lava, associa- 

 ted with a fauna whose general facies is ancient, though 

 not sufficiently definite to establish the pre-glacial exist- 

 ence of man paleontologically. The pre-glacial age ol all 

 these remains may be, however, inferred from the evidence 

 furnished by the sub-asrial erosion of the valley of Le 

 Puy and the glacial erosion of the adjacent mountains of 

 Coutal ; though the testimony can hardly be regarded as 

 conclusive. The finding of a human cranium in auriferous 

 gravels overlain by extensive lava-beds probably of pre- 

 glacial age in California, associated with organic remains 

 of rather more southern type than those of Le Puy, as 

 attested by Whitney, affords more satisfactory evidence of 

 the pre-glacial existence of man. Along the Delaware 

 river in New Jersey numerous rough-stone implements 

 have been collected by Abbott from a table drift, or mass 

 of re-arranged glacial matter, which is destitute of organic 

 remains. " From a rather incomplete study of the ground, 

 the only view I could take of these remains was that they 

 were scattered on the surface of the earth to the north- 

 ward before the last glacial period ; that they were thrust 

 before the glacier during its period of greatest extension, 

 and deposited in the beds where they now lie by the action 

 of water, while the above underwent a slight submerg- 

 ence " (p. 134). These chipped flints of the Delaware, 

 no less than the Le Puy and Calaveras eronia, indicate 

 that even at this early day man had attained a social con- 

 dition similar to that of the European stone age ; and 

 hence that during the vast intervening period, the dura- 

 tion of which was probably not less than 200,000 years, 

 or forty times the term of recorded history, there was al- 

 most no progress in the latterly rapid process of intel- 

 lectual development. 



XII. The movement of glaciers. — "It is to De Saussure 



that we owe the first hypothesis concerning glacial mo- 

 tion " (p. 140) ; his view being embraced in the sugges- 

 tion that the ice slid bodily downward in a solid mass, the 

 sliding being facilitated by melting of the basal portion 

 of the ice through the influence of proper terrestrial heat. 

 The utter inadequacy of this hypothesis must, however, 

 have been apparent to its talented author ; — indeed — "we 

 are forced to believe that this statement does not repre- 

 sent his conclusions" (p. 140). Charp a utier subsequently 

 suggested that the motion is due to the nightly freezing 

 and expansion of the water taken into the interstices of 

 the ice during the day ; but this hypothesis is also inade- 

 quate. Still later the solution of the problem was under- 

 taken by Agassiz, who devised a critical series of experi- 

 ments to determine the empirical laws of motion of the 

 glaciers. The plan was to plant a line of stakes across 

 the ice-stream, and to measure their absolute and relative 

 movement at the end of a year. During the first season 

 the entire series was overthrown by the superficial melt- 

 ing of the ice ; but the stakes were again more firmly 

 planted. Among the naturalists who visited his camp on 

 the glacier was J. D. Forbes, whose contributions to gla- 

 cial physics are well known. " While the guest of Agas- 

 siz, Professor Forbes made his first acquaintance with ex- 

 isting glaciers. Owing to his superior training in the 

 branches of learning that this peculiar problem called for, 

 he soon saw that the method that Agassiz was using was, 

 by a slight modification, capable of a more speedy solution 

 than his Swiss host could obtain under the conditions of 

 his experiment. Agassiz planted a row of stakes across 

 the glacier, but proposed to wait, with the patience that 

 characterized his mind, until after a winter, to read the 

 answer he sought. Mr. Forbes saw that with a transit 

 or theodolite he could, in a few days at most, see how the 

 stakes were moved, and so anticipate the results his host 

 was seeking. With this plan in mind he went to the Mer 

 de Glace, set up a line of stakes in the precise position 

 devised by Agassiz, and within a month proved that the 

 ice moves most rapidly in its middle parts, and not, as had 

 been supposed, more quickly upon the sides of the stream ; 

 this result he hastened to make public " ( p. 142 ). These, 

 as well as later observations, show the laws of mo- 

 tion of glaciers correspond to those of moving liquids. 

 Somewhat previously Renda had reached a similar con- 

 clusion. Forbes soon after enunciated the viscous the- 

 ory of ice-motion, illustrating " his conception of glacial 

 movement by frequent reference to other substances, the 

 the viscosity of which we recognize in ordinary experi- 

 ence, such as tar, wax, or molasses " ( pp. 143-4 ). " In 

 the hands of his followers this theory has sometimes as- 

 sumed a different shape * * * ; it is then made to mean 

 that the ultimate tangible elements of the glacier, the bits 

 of ice into which it is divided, slide over each other, as, 

 for instance a heap of peas when poured on a sloping 

 surface " ( p. 144 ); This captivating hypothesis has not, 

 however, been widely adopted. Next followed the frac- 

 ture-and-vegetation hypothesis of Tyndall ; but neither 

 has this view commanded general assent. Still later Croll 

 enunciated the hypothesis of successive melting and 

 freezing of the molecules of the ice ; "each molecule, as 

 it is melted, parting with its heat to its neighbor on the 

 inward side of the ice, and returning to the solid state, 

 shortly to be remelted by the heat transmitted by its outer 

 neighbor " (p. 145 ). There are certain phenomena, how- 

 ever, which this inherently probable hypothesis fails to 

 explain. There is then the view in which the motion is re- 

 ferred to momentary melting, through the influence of 

 pressure, of the particles of ice from time to time sub- 

 jected to unusual strain ; but, like the last, this hypothe- 

 sis is alone incompetent to explain all the phenomena of 

 ice-motion. Finally there is the sliding theory of Hopkins, 

 which is in conflict with all we know of glacial move- 

 ment. Examples of glacier motion are furnished by the 

 annual snows of New England hill-sides ; and the energy 

 of this motion is well illustrated by a phenomenon observed 



