chap. xi. concluding Remarks on. 349 



maminifers which so lately swarmed over the two 

 Americas. 



Summary and concluding remarks on the Pam~ 

 pean Formation. — One of its most striking features is 

 its great extent ; I passed continuously over it from the 

 Colorado to St. Fe Bajada, a distance of 500 geographical 

 miles ; and M. d'Orbigny traced it for 250 miles farther 

 north. In the latitude of the Plata, I examined this 

 formation at intervals over an east and west line of 

 300 miles from Maldonado to the River Carcarana ; and 

 M. d'Orbigny believes it extends 100 miles farther 

 inland : from Mr. Caldcleugh's travels, however, I should 

 have thought that it had extended, south of the Cordo- 

 vese range, to near Mendoza, and I may add that I 

 heard of great bones having been found high up the 

 River Quint o. Hence the area of the Pampean forma- 

 tion, as remarked by M. d'Orbigny, is probably at least 

 equal to that of France, and perhaps twice or thrice 

 as great. In a basin, surrounded by gravel-cliff (at a 

 height of nearly 3,000 feet), south of Mendoza, there 

 is, as described in the tenth chapter, a deposit very like 

 the Pampean, interstratified with other matter ; and 

 again at S. Julian's, in Patagonia, 560 miles south of 

 the Colorado, a small irregular bed of a nearly similar 

 nature contains, as we have just seen, mammiferous 

 remains. In the provinces of Moxos and Chiquitos 

 (1,000 miles northward of the Pampas), and in Bolivia, 

 at a height of 4,000 metres, M. d'Orbigny has described 

 similar deposits, which he believes to have been formed 

 by the same agency contemporaneously with the Pam- 

 pean formation. Considering the immense distances 

 between these several points, and their different heights, 

 it appears to me infinitely more probable, that this 

 similarity has resulted not from contemporaneousness of 

 origin, but from the similarity of the rocky framework 



