chap. xii. Temperature of Tertiary Period. 413 



generally so tropical a genus, is at present confined on 

 the west coast to colder or more southern latitudes than 

 it was during the tertiary period. The Trochus collaris, 

 moreover, and, as we have just seen according to Mr. 

 Sowerby, two or three other species, formerly ranged 

 from Navidad as far south as Santa Cruz in lat. 50°. If, 

 instead of comparing the fossils of Navidad, as we have 

 hitherto done, with the shells now living on the west 

 coast of South America, we compare them with those 

 found in other parts of the world, under nearly similar 

 latitudes ; for instance, in the southern parts of the 

 Mediterranean or of Australia, there is no evidence 

 that the sea off Navidad was formerly hotter than what 

 might have been expected from its latitude, even if it 

 was somewhat warmer than it now is when cooled by 

 the great southern polar current. Several of the most 

 tropical genera have no representative fossils at Navi- 

 dad ; and there are only single species of Cassis, Pyrula, 

 and Sigaretus, two of Pleurotoma and two of Terebra, 

 but none of these species are of conspicuous size. In 

 Patagonia, there is even still less evidence in the 

 character of the fossils, of the climate having been 

 formerly warmer. 1 As from the various reasons already 

 assigned, there can be little doubt that the formations 

 of Patagonia and at least of Navidad and Coquimbo in 

 Chile, are the equivalents of an ancient stage in the 

 tertiary formations of the northern hemisphere, the 

 conclusion that the climate of the southern seas at this 

 period was not hotter than what might have been ex- 

 pected from the latitude of each place, appears to me 

 highly important ; for we must believe, in accordance 



1 It may be worth while to mention that the shells living at the 

 present day on this eastern side of S. America, in lat. 40°, have 

 perhaps a more tropical character than those in corresponding 

 latitudes on the shores of Europe : for at Bahia Blanca and S. Bias, 

 there are two fine species of Voluta and four of Oliva. 



