GEOLOGIC AND PETROGRAPHIC NOTES ON THE 

 REGION ABOUT CAICARA, VENEZUELA 1 



T. A. BENDRAT 



Turners Falls, Massachusetts 



In the winter of 1908-9, the writer carried on some independent 

 studies along petrographic and geologic lines, in the interior of 

 Venezuela, choosing for his field of investigation the region imme- 

 diately west of the so-called "El Caura District," at the famous 

 bend of the Orinoco, and mapping an area of 1,400 sq. km., which 

 was hitherto very little known. While the general results of this 

 survey have been summed up elsewhere, 2 it is on the main geologic 

 and petrographic features of the region that the writer wishes to 

 offer the following observations. 



GEOLOGIC STRUCTURE 



I. THE BED ROCK 



The bed rock consists of a series of granites and gneisses which, 

 wherever they come to the surface, show a predominance of the 

 gneiss over the granite. These granites and gneisses rise from 

 the bottom of the Orinoco channel; constitute the base of many 

 of the islands; are exposed in the banks of the river, particularly 

 in the dry season; and back from the river form the bulk of the 

 "Cerros." These cerros are hills and small mountains which rise 

 above the plain of the sabana. In general they increase in height 

 in proportion to increasing distance from the Orinoco, and may 

 be regarded as outliers of the Guiana mountain system lying to the 

 south. These cerros are probably to be considered as portions of 

 the great series of granites and gneisses which have most effect- 

 ively resisted disintegration, partly because a skeleton of numer- 



1 The writer desires to express at this place his high obligations to Professor 

 B. K. Emerson of Amherst College who was kind enough to have the petrographic 

 microscopes of Smith College, Northampton, Mass., placed as his disposal. 



2 Petermann's Geogr. Mittettungen (1910), Bd. 56, v; Geographen Kalender 

 (1909), 221. 



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