144 



DISTRIBUTION OF PLANTS. 



some miles beyond Yaso, being on one side of the river of granite, 

 and on the other side of porphyry ; at length, the two formations met 

 in a mountain-ridge, and were traced to within a very short distance 

 of each other. The porphyry was observed to be normal and well 

 characterized, much resembling the Swedish and that of the vicinity 

 of Boston. The bed is the source of the numerous pebbles of similar 

 consistence on the sea-shore North and South of Callao; and proved 

 extensive, but does not exclusively constitute the trap formation. 

 This extends up the basal portion of the Andes; being perhaps 

 twenty geographical miles wide; but its Eastern margin was not defi- 

 nitely ascertained. 



The Andes presented in fact a good deal of the character and out- 

 line of an immense ledge of sedimentary rock: contemporaneous even 

 with the strip along the sea-coast; for an Ammonite, picked up by 

 myself within thirty feet of the perpetual snow, proved to be a third 

 allied species. '■'■Coal of a highly bituminous quality" was said to be 

 procured in the upper district, and to be "used extensively at Pasco 

 and other places." At Baiios, we observed a quantity of gypsum, 

 said to have been " brought for manure from the vicinity of Casa- 

 Cancha." We visited also the copious Itot-sprmg near Banos ; but 

 nowhere on the Peruvian Andes could we hear of volcanoes. As far 

 as examined by myself, the crest and upper portion of the Peruvian 

 Andes consisted mainly of conglomerate ; the included pebbles being 

 very regular in shape, and as smooth and polished as though sea- 

 washed: it is true, the pebbles formed in the rapidly descending tor- 

 rents around were very similar, and smoother than I ever before 

 remarked in fresh water : the conglomerate in some places consisted 

 of very diminutive pebbles, but hardly became normal sandstone. — 

 The silver mine at Alpamarca, on an eminence reaching nearly to the 

 perpetual snow, was observed to be contained in compact bluish rock, 

 probably impure limestone ; traversed at least by numerous seams of 

 calcareous spar, of hard, opaque consistence, and having something of 

 the lustre of satin spar. The snowy peaks on the crest of the Andes 

 farther North, proved to be composed of the same rock, in a similar 

 manner seamed with calcareous spar; and lower down, at Banos, we 

 found the rock burned for lime. — Owing, it would seem, in part to the 

 slate-colored rock, the peaks of the Peruvian Andes, wherever free 

 from snow and from vegetation, were black and sombre ; presenting 

 nothing of the play of colors witnessed in Chili. 



