PLATEAU OF CAXAMARCA. 297 



is still 4260 English feet above the level of the sea. A 

 few wretched huts, surrounded by the same wool or cotton- 

 trees (Bombax discolor) which we had first seen on the 

 banks of the Amazons, were called an Indian village. 

 The scanty vegetation of the valley bears some resemblance 

 to thai of the province of Jaen de Bracamoros, but we 

 missed the red groves of Bougainvillsea. This valley is one 

 of the deepest with which I am acquainted in the chain of 

 the Andes : it is a true transverse valley directed from east 

 to west, deeply cleft, and hemmed in on the two sides by 

 the Altos de Aroma and Guangamarca. In this valley 

 recommences the same quartz formation which we had 

 observed in the Paramo de Yanaguanga, between Micui- 

 pampa and Caxamarca, at an elevation of 11720 English 

 feet, and which, on the western declivity of the Cordillera, 

 attains a thickness of several thousand feet, and was long 

 an enigma to me. Since von Buch has shown us that the 

 cretaceous group is also widely extended in the highest chains 

 of the Andes, on either side of the Isthmus of Panama, 

 the quartz formation which we are now considering, which 

 has perhaps been altered in its texture by the action of 

 volcanic forces, may be considered to belong to the Quader- 

 sandstein, intermediate between the upper part of the chalk 

 series, and the Gault and Greensand. On quitting the mild 

 temperature of the Magdalena valley we had to ascend again for 

 three hours the mountain wall of 5120 English feet, opposite 

 to the porphyritic group of the Alto de Aroma. The change 

 of climate in so doing was the more sensible, as we were 

 often enveloped in the course of the ascent in a cold fog. 



