﻿I860.] 



FORBES BOLIVIA AND PERU. 



9 



The strike and dip of the rocks, when not otherwise stated, are 

 given with reference to the magnetic meridian. 



In the arrangement of my notes it was found most satisfactory to 

 classify them according to the geological age of the deposits in ques- 

 tion, commencing with the most recent. 



1. Tertiary and Diluvial Formations of the Coast. — The older 

 Tertiary beds of shells so characteristic of many parts of the Chilian 

 line of coast do not appear to present themselves from Mexillones 

 northward to Arica ; but we find at intervals shell-beds, containing 

 exclusively shells of species now inhabiting these waters, elevated to 

 a small height above the sea : I did not, however, observe any beds 

 reaching an elevation of 40 feet above the present sea-level ; and 

 although the whole line of coast shows unquestionable signs of re- 

 cent elevation, still the evidence is not so satisfactory, and appears 

 to point out a much more irregular action than further south along 

 the Chilian coast-line. 



At Cobija 1 discovered a bed of shells in the immediate neigh- 

 bourhood, to the south of the port, about 25 feet above the present 

 sea-level; and, on examination, this was found to contain only species 

 at present inhabiting these waters. Among these shells I recog- 

 nized the following genera : — 



Concholepas. Fusus. Patella. 



I found also fragments of an Echinus and bones of a Seal. Whilst 

 digging in this bed, I came upon a small piece of wood in a decayed 

 state, which evidently had been shaped by human hands, and bore 

 marks of having been cut by a sharp tool, most likely of steel, as 

 some of the cuts appeared much too defined to be attributed to a 

 stone or other dull instrument. 



On the rocks close to the town are some deposits of guano, which 

 are being worked to advantage, although in quality and thickness 

 much inferior to the guano from the Chinchas Islands pertaining to 

 Peru. These deposits are situated at from 20 to 40 feet above the 

 sea-level, and in appearance are very similar to the Chinchas beds 

 on a small scale. 



On the surface of these deposits, and also between the beds of the 

 same, my attention was attracted by a crust or bed of a harder sub- 

 stance, of a light-brown colour, varying in thickness from a few 

 inches to one or more feet, and possessing a semicrystalline and 

 rather saline appearance, with occasionally a faint ammoniacal odour. 

 On examination I found it to contain a large amount of ammonia 

 in a state of combination ; and, at the request of the Bolivian Go- 

 vernment, it was analysed by Mr. Prancis Ignacio Eickard, of Val- 

 paraiso, who obtained the following per centage composition : — 



Mactra. 



Venus (2 species). 



Mytilus. 

 Tellina, 



Oliva. 

 Trochus. 

 Turbo. 

 Turritella. 



Fissurella (2 species). 



Chiton. 

 Serpula. 

 Balanus. 



