﻿I860.] 



FORBES BOLIVIA AND PERU. 



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03 s£ 



as possible, and was only enabled to make observations on tbe imme- 

 diate route ; so tbat the section of this basin is to be regarded as a 

 sketch merely ; but, at the same time, I believe that it represents 

 pretty accurately the real state of the case. 



Starting from the eastern portion of this section, from Hachecache, 

 after traversing the volcanic rocks and a series of highly contorted 

 beds supposed by D'Orbigny to be of Devonian age, we arrive at the 

 Carboniferous series, represented in the section as being unconform- 

 able to, and abutting up against, the last-mentioned beds, owing to 

 ^ ^ the occurrence of a fault : 



this appeared to be the case ; 

 but I admit that it is not de- 

 termined with as much pre- 

 cision as I could have wished. 



The strata first met with 

 are red sandstones covered by 

 \\ \ \ \ g? a .S some white sandstones, both 



of which alternate with and 

 are succeeded by a rather 

 nondescript rock, probably 

 igneous, as the overlying beds 

 of shales appeared to be al- 

 tered as if by such agency; 

 above these are some thin 

 calcareous beds (fossiliferous), 

 but the fossils I met with were 

 too indistinct for determi- 

 nation; and then greenish 

 O/X^W \ ^ « w B " shales, compact greenish 

 shales, and red shales, suc- 

 ceeded by beds of red sand- 

 stone, forming the beach at 

 Tiquina, at the Lake of Ti- 

 ticaca. 



The Straits of Tiquina, 

 which here separate the lower 

 from the upper part of the 

 lake, appear to the eye not 

 to attain a breadth of more 

 than from one-half to one 

 English mile across, and, 

 from the appearance of the 

 stratification on both sides, 

 are most probably the seat 

 of a great fault which has 

 broken up the continuity of 

 the Carboniferous series. 

 Hitherto in the section 

 these strata have all shown a dip to the westward, at pretty high 

 angles, up to Tiquina : on crossing the straits, however, we meet 



VOL. XVII. PABT I. E 



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