30 



MR. J. A. DOUGLAS OX GEOLOGICAL SECTIONS [April 1914, 



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thickness of the chocolate sandstones to the westward, which for 



some distance dip in the same direction. 



My reason for regarding the sandstones 

 dj and conglomerates of this series as of 



much earlier date than the gypsiferous 

 Cretaceous sandstones is, that they can 

 be traced far to the north along the west 

 side of Lake Titicaca, where they appear 

 to be continuous with the limestones and 

 sandstones of Carboniferous or Permo- 

 Carboniferous age, and are distinct from 

 the overlying transgressive Cretaceous 

 deposits. 



(c) The Carboniferous or Pernio - 

 Carboniferous Rocks of the 

 Titicaca District. 



Though a few derived fossils are met 

 with in the conglomerate-beds of Coniri, 

 rocks which can be definitely assigned to 

 the Carboniferous formation are nowhere 

 visible in situ along the Arica-La Paz 

 section, and as a geological description 

 of the country would appear incomplete 

 without some reference to this formation, 

 a slight digression must be made to discuss 

 its development in the region of Lake 

 Titicaca, which lies some 30 miles away 

 to the north. Here an excellent section 

 is visible along the shores of the lake at 

 the Straits of Tiquina, on the Peninsula 

 of Copacabana and on the Island of the 

 Sun. 



The rocks, which consist of red sand- 

 stones and breccias, yellow and black 

 shales, and grey cherty limestones, though 

 strongly folded, failed to reveal evidence 

 of the intense overfolding depicted by 

 Forbes. 1 



Unfortunately, several of my notes and 

 - .1 an excellent map of the district were, 



among other possessions, stolen by a 

 boatman who transported our luggage 

 across the lake, and consequently the 

 section cannot be produced in the detail 

 with which it was studied; it will serve, 

 however, to show my interpretation of 



1 Q. J. G. S. vol. xvii (1861) p. 49 ; fig. 5. 



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