■ A Geological Retros^oect of the Year 1802. 199 



sea or by a deluge on land, but that the species of elephant, 

 rhinoceros, and other animals inhabited these northern regions, 

 where by their natural constitution they were fitted to endure the 

 severity of the Siberian climate. " The rhinoceros of Wilui," he 

 remarks, " certainly lived on the confines of the Polar Circle, and 

 was exposed to the same cold while alive, by which, when dead, its 

 body has been so long and so curiously preserved " ( § 417). He 

 concluded his argument by suggesting that the crowded aggregates 

 of these mammalian remains may have been connected with the 

 migrations of the animals. 



Another subject which has been much discussed since Playfair's 

 time — the origin of lakes — did not escape his keen scrutiny of the 

 surface of the land. It received from him a candid and cautious 

 handling, which has not always been imitated by his successors in 

 the discussion of this questioo. He recognised that "a lake is but 

 a temporary and accidental " feature in topography, seeing that it is 

 obviously being filled up by the unceasing transport of sediment 

 into it from the surrounding ground, and hence that it must be 

 " but modern compared with many of the revolutions that have 

 happened on the surface of the earth" (§§ 319, 326). But when he 

 tried to picture to himself the natural process whereby the lake has 

 been formed, he had frankly to admit the difficulty of the problem. 

 " Some cause," he remarks, " seems to act, if not in the generation, 

 yet certainly in the preservation of lakes, with which we are but 

 little acquainted" (§ 325). He suggests two possible modes of 

 their origin. In the first place, they may arise from the solution 

 and removal of such a soluble material as rock-salt, and he foretells 

 that this must eventually happen in the salt district of Cheshire. 

 He adds that some effect of the same kind may have taken place on 

 the site of the Lake of Geneva, near to which salt-springs rise to the 

 surface. In the second place, he points out that lakes may be 

 produced by the unequal elevation and subsidence of land, whereby 

 hollows arise on the surface which become water-filled basins 

 (§ 327). There can be no doubt that both these suggestions 

 indicate vercB causce which have at different times and places given 

 rise to lakes. Playfair evidently could not conceive that any 

 natural agency can excavate basins out of solid rock. Though he 

 had. recognised the great transporting power of glaciers, he did not 

 perceive that they also possess an erosive capacity which enables 

 them to grind down, smooth, and polish the hardest rocks, and 

 under peculiar conditions to hollow them into basin-shaped cavities, 

 which on the retreat of the ice become tarns or lakes. 



Like Hutton, Playfair exaggerated the influence of underground 

 heat in the formation and consolidation of rocks. Thus he adopted 

 and stoutly maintained his master's contention that flints and agates 

 have been introduced in a molten condition into the rocks among 

 which they are found. He never grasped the idea of the great 

 solvent power of water and the permeability of rocks by aqueous 

 solutions. Hence he deliberately rejected the proposition that 

 consolidation of rocks may be brought about by infiltration 



