PLATEAU OP CAXAMARCA. 423 



This fall, and the consequent blocking up of the channel, arrested 

 the flow of the stream; and the inhabitants of the village of Puyaya, 

 situated below the Pongo de Rentema, saw with alarm the wide 

 river-bed entirely dry; but after a few hours the waters again forced 

 their way. Earthquake movements are not supposed to have occa- 

 sioned this remarkable occurrence. The powerful stream appears to 

 be, as it were, incessantly engaged in improving its bed ; and some 

 idea of the force which it exerts may be formed from the circum- 

 stance that, notwithstanding its breadth, it is sometimes so swollen 

 as to rise more than 26 English feet in the course of twenty or thirty 

 hours. 



We remained for seventeen days in the hot valley of the Upper 

 Maranon or Amazons. In order to pass from thence to the shores 

 of the Pacific, the Andes have to be crossed at the point where, be- 

 tween Micuipampa and Caxamarca (in 6 57' S. lat. and 78 34' W. 

 long, from Greenwich), they are intersected, according to my obser- 

 vation, by the magnetic equator. Ascending to a still higher eleva- 

 tion among the mountains, the celebrated silver mines of Chota are 

 reached, and from thence with a few interruptions the route descends 

 until the low grounds of Peru are gained ; passing intermediately 

 over the ancient Caxamarca, where 316 years ago the most sangui- 

 nary drama in the annals of the Spanish Conquista took place, and 

 also over Aroma and Grangamarca, Here, as almost everywhere in 

 the Chain of the Andes and in the Mexican Mountains, the most 

 elevated parts are picturesquely marked by tower-like outbreaks of 

 porphyry (often columnar), and trachyte. Masses of this kind give 

 to the crest of the mountains sometimes a cliff-like and precipitous, 

 and sometimes a dome-shaped character. They have here broken 

 through calcareous rocks, which, both on this and on the northern 

 side of the Equator, are largely developed ; and which, according to 

 Leopold von Buch's researches, belong to the cretaceous group. 

 Between G-uambos and Montan, 12,000 French (12,790 English) 

 feet above the sea, we found marine fossils ( n ) (Ammonites, nearly 

 fifteen English inches in diameter, the large Pectan alatus, oyster 

 shells, Echini, Isocardias, and Exogyra polygona). A species of 

 Cidaris, which, according to Leopold von Buch, cannot be distin- 

 guished from that which Brongniart found in the lower part of the 



