No. 479] EXTINCTION OF MAMMALIA 



771 



creation, a new animal or plant, an additional snow-clad moun- 

 tain, any permanent change, however slight in comparison to the 

 whole, gives rise to a new order of things, and may make a material 

 change in regard to some one or more species. Yet a swarm of 

 locusts, or a frost of extreme intensity, or an epidemic disease, 

 may pass away without any great apparent derangement; no 

 species may be lost, and all may soon recover their former rela- 

 tive numbers, because the same scourges may have visited the 

 region again and again, at preceding periods. Every plant that 

 was incapable of resisting such a degree of cold, every animal 

 which was exposed to be entirely cut off by an epidemic or by 

 famine caused by the consumption of vegetation by the locusts, 

 may have perished already, so that the subsequent recurrence of 

 similar catastrophes is attended only by a temporary change." 



Even as a geologist Lyell was very cautious, certainly too 

 cautious, in estimating the destructive influence of geologic and 

 physiographic changes. In 1863 {Antiquity of Man,^ p. 374), he 

 observed : 



"It is probable that causes more general and powerful than the 

 agency of Man, alterations in climate, variations in the range of 

 many species of animals, vertebrate and invertebrate, and of 

 plants, geographical changes in the height, depth, and extent of 

 land and sea, some or all of these combined, have given rise, in a 

 vast series of years, to the annihilation, not only of many large 

 mammalia, but to the disappearance of the Cyrena fnminalis, 

 once common in the rivers of Europe, and to the different range or 

 relative abundance of other shells which we find in the European 

 drifts." 



Charles Darwiir' pursues a line of thouu'ht exactly prophetic to 

 that of Lvell in discussing the Plioceiu" and post-Pliocene ex- 

 tinction of the large mammals of South America. He dismisses 

 any catastrophic causes and in general attributes extinction to a 

 cessation of those world-wide conditixjns of life which were favor- 

 able to the larfjer quadrupeds in Europe, Asia, Australia, North and 



'Lyell, Charles. Geolmiicnl Kvuhnres oj the Antiquity of Man, 2d ed., 

 revised, 8vo. London, 1863, p. 



'Darwin, Charles. Journal oj Resrarchr.^ . . ..Voyage of H. M. S. Beagle,. 

 Svo, 1834, pp. 169, 170. 



