PLATEAU OF CAXAMAKCA. 403 



Chota. Then, after having passed the ancient Caxamarea 

 (the scene, 316 years ago, of the most sanguinary drama in 

 the history of the Spanish Conquista), and also Aroma and 

 Gangamarca, the route descends, with some interruptions, 

 into the Peruvian lowlands. Here, as in nearly all parts of the 

 Andes, as well as of the Mexican Mountains, the highest points 

 are picturesquely marked by tower-like masses of erupted 

 porphyry and trachyte, the former frequently presenting 

 the effect of immense columns. In some places these masses 

 give a rugged cliff-like aspect to the mountain ridges ; and 

 in other places they assume the form of domes or cupolas. 

 They have here broken through a formation, which, in South 

 America, is extensively developed on both sides of the equa- 

 tor, and which Leopold von Buch, after profound research, 

 has pronounced to be cretaceous. Between Guambos and 

 Montan, nearly 12,800 feet above the level of the sea, 

 we found marine fossils (11) (Ammonites about 15 inches 

 in diameter, the large Pecten alatus, oyster- shells, Echini, 

 Isocardias, and Exogyra polygona). A species of Cidaris, 

 which, in the opinion of Leopold von Buch, does not differ 

 from one found by Brongniart in the old chalk at the Perte du 

 llhone, we collected in the basin of the Amazon at Tomependa, 

 and likewise at Micuipampa; that is to say, at elevations 

 differing the one from the other by no less than 10,550 feet. 

 In like manner, in the Amuich chain of the Caucasian 

 Daghestan, the chalk of the banks of the Sulak, scarcely 530 

 feet above the level of the sea, is again found on theTchunum, 

 at the elevation of full 9600 feet, whilst, on the summit 

 of the Shadagh Mountain, 13,950 feet high, the Ostrea 

 diluviana (Goldf.), and the same chalk, present themselves. 

 Abich's admirable Caucasian observations furnish the most 

 decided confirmation of Leopold von Buch's geognostic views 

 respecting the cretaceous Alpine development. 



From the solitary farm of Montan, surrounded with flocks 

 of Lamas, we ascended further southward the eastern declivity 



2 d 2 



