chap. xiv. Neocomian Fossils. 491 



4. Cucullaea, corresponding in form to C. hngirostris, so frequent 



in the upper Jurassic beds of Westphalia. 

 6. Ammonites, resembling A. biplex. 



Von Buch concludes that this formation is intermediate 

 between the limestone of the Jura and the chalk, and 

 that it is analogous with the uppermost Jurassic beds 

 forming the plains of Switzerland. Hence M. d'Orbigny 

 and Von Buch, under different terms, compare these 

 fossils to those from the same late stage in the Secondary 

 formations of Europe. 



Some of the fossils which I collected were found a 

 good way down the western slope of the main ridge, 

 and hence must originally have been covered up by a 

 great thickness of the black shaly rock, independently 

 of the now denuded, thick, overlying masses of red 

 sandstone. I neglected at the time to estimate how 

 many hundred or rather thousand feet thick the 

 superincumbent strata must have been : and I will 

 not now attempt to do so. This, however, would have 

 been a highly interesting point, as indicative of a great 

 amount of subsidence, of which we shall hereafter find 

 in other parts of the Cordillera analogous evidence 

 during this same period. The altitude of the Peu- 

 quenes range, considering its not great antiquity, is 

 very remarkable ; many of the fossils were embedded at 

 the height of 13,210 feet, and the same beds are pro- 

 longed up to at least from 14,000 to 15,000 above the 

 level of the sea. 



TJie Portillo or Eastern Chain. — The valley of 

 Tenuyan, separating the Peuquenes and Portillo lines, 

 is, as estimated by Dr. Gillies and myself, about twenty 

 miles in width ; the lowest part, where the road crosses 

 the river, being 7,500 feet above the sea-level. The 

 pass on the Portillo line is 14,865 feet high (1,100 feet 

 higher than that on the Peuquenes), and the neigh- 

 22 



