66 



KNOWLEDGE 



[April 1, 1892. 



masticating apparatus in the one than in the other is 

 apparent. 



In modern Elephants, the six molar teeth on either side 

 of each jaw are all that are ever developed. This is, 

 however, hy no means the case with some of the earlier 

 Elephants," and with most of the Mastodons. In these 

 animals, when the second and third molars became worn 

 out. they were succeeded vertically by much smaller teeth, 

 from which we learn that the first three molars of the 

 modern Elephants really correspond to the milk-teeth of 

 other j\Iammals, which, as we all know, are succeeded 

 vertically by some of the teeth of the permanent series. '^ 

 This succession of the teeth shows us, therefore, another 

 point in which Mastodons tend to connect modem 

 Elephants with ordinary Ungulates. 



We mi'^ht go further and enter upon the consideration 

 of some of the structural peculiarities presented by the 

 soft parts of Elephants. Enough has, however, been 

 stated to show that while these animals have preserved 

 a very ancient type of structure in their limbs, they 

 have acquired a very special modification in the structure 

 and mode of succession of their teeth. And it is highly 

 probable that it is owing to this particular specialization 

 that Elephants have survived to our own day, while all 

 the other plantigrade and five-toed primitive Ungulates 

 have completely passed away ; while it is almost certain 

 that it is this feature alone which has enabled them to 

 attain the gigantic bulk which forms one of their most 

 striking features. In regard to their evolution perhaps no 

 group shows more clearly than that of the Elephants how 

 exceedingly important is the study of fossils to elucidate 

 the relations of existing animals. Had we only the two 

 living species of Elephants to deal with, we should never 

 have had the least inkling of the manner in which 

 they were related to other Ungulates, imperfect as our 

 knowledge of the relationship still is. Moreover, from 

 the distribution of these two species, it would have been 

 naturally inferred that Elephants were creatures suited 

 solely to tropical or sub-tropical climates. The discovery 

 of frozen carcases of the Mammoth — a species closely 

 relatedto the Indian Elephant — in the Siberian "tundras" 

 shows, however, that this animal ( Fig. 1 ) was suited to dwell 

 in at least comparatively cold regions, although it is probable 

 that the climate of Siberia was formerly not so rigorous 

 as it is at present. To withstand the cold of these 

 northern regions the Mammoth was protected by a coat 

 of long reddish hair, beneath which was a shorter covering 

 partaking more of the nature of wool. Along the borders 

 of the Arctic Ocean for hundreds of miles Mammoth 

 remains are met with in incredible quantities ; and it is 

 still one of the puzzles of geology to account adequately 

 and satisfactorily for the maimer in which these creatures 

 perished, and how their bodies were buried beneath the 

 frozen soil before decomposition had begun its work, for it 

 is hai'dly possible to believe that they lived in a climate so 

 rigorous that their bodies would have been frozen on the 

 surface of the ground immediately after death. 



Another rude shock to our common ideas of Elephantine 

 nature is afforded by the extinct Elephants of Malta, 

 which show us that gigantic size is not a necessary 

 concomitant of the group ; and that when the area in 

 which a species dwelt was small, the size of the species 

 itself was proportionately reduced. These little Maltese 

 Elephants were very closely allied to the living African 

 species, but whereas " .Jumbo " attained eleven feet in 

 height, and wild specimens of the African Elephant may 

 be still larger, the smallest of the Maltese species was 



* See article on " Teeth and their Variations." 



scarcely taller than a donkey. So small, indeed, are the 

 bones and teeth of this species exhibited in the Natural 

 History Museum, that it is sometimes difficult to convince 

 people that they really belonged to Elephants at all. 



As regards their distribution. Elephants and Mastodons 

 formerly roamed over the whole world with the exception 

 of Australia ; true Elephants ranging over the whole of 

 the Northern Hemisphere, while Mastodons extended as 

 far south in the New World as the confines of Patagonia. 

 It is in the north-east of India, Burma, and the islands of 

 the Malayan region that the fossil Elephants connecting the 

 living species with the Mastodons are alone found ; and it 

 is thus probable that from these regions the true Elephants 

 migrated westward into Europe and Africa, while the 

 Mammoth in later times crossed from Asia into Alaska by 

 way of Behring Straits. That the Mammoth, which ranged 

 from the Arctic regions to the Alps and Pyrenees, was a 

 contemporary of the primeval hunters of Europe is now a 

 well-established fact, but it appears that throughout the 

 Old World Mastodons had utterly died out before the 

 advent of man. In the New World, however, the con- 

 tinuity between the old and the new fauna was more fully 

 sustained, the Missouri Mastodon having survived well 

 into the human period, so that we have in this survival a 

 good instance of the vast changes that have taken place in 

 the fauna of the globe within what we may metaphorically 

 call the memory of man. 



THEORIES OF GLACIER-MOTION. 



By the Kev. H. N. Hutchinson, B.A., F.G.S. 



THEEE are few subjects in physical geology which 

 have excited more interest than that of the motion 

 of Glaciers. Ice is a very peculiar substance ; 

 and some of its properties appear so contradictory 

 to others, that scientific men of high attainments 

 have been greatly puzzled by its behaviour as manifested 

 in Glaciers. Hence when we come to consider how, or 

 why, Glaciers flow down their valleys, we find a great 

 diversity of opinion. Readers of Knowledge may there- 

 fore be glad to have a brief account of the different theories 

 of Glacier-motion which have from time to time been 

 brought forward, together with some indication as to their 

 relative merits. 



First, with regard to the origin of the ice itself; most of 

 our readers will be aware that Glaciers are fed by the snow- 

 fields above them. So it may almost be said that a 

 Glacier is snow at one end and ice at the other. How 

 then does the change from snow to ice take place '? 

 Pressure, as every school-boy knows, will convert a handful 

 of newly-fallen snow into a hard mass, and if the pressure 

 be continued, the hardened snow will become ice. It is 

 partly this property of snow which makes a Glacier, or 

 ice-river possible. When snow has accumulated to a 

 considerable depth, its own weight squeezes down its 

 lower strata ; and the underlying portions of snow are 

 finally compacted together until they become true ice. 

 But another cause is at work helping to bring about the 

 same result. By day, when the sun shines upon the snow, 

 or warm air passes over its surface, the surface-layer 

 gets partially melted, the water thus formed trickles down 

 into other snow below, and there solidifying, when night 

 comes and a fall in temperature takes place becomes 

 part of the great mass of ice. Summer and winter 

 act in the same way as day and night, so that much 

 of the winter's snow gets melted and turned to ice. Thus, 

 partly by thawing and freezing, and partly by pressure 



