

Bendrat — Notes on Region about Caicara, Venezuela. 451 



In favor of the other view, that the gneiss is sedimentary in 

 origin, seems only the circumstance that the gneiss in all the 

 different cerros is to some, and in that of the Cerro de Caicara 

 to a remarkable, extent impregnated with iron oxides, although 

 no pronounced ferruginous beds have been found. 



Consequently we may conclude that the gneiss is of igneous 

 origin. From the pronounced similarity in composition of 

 both granites and gneisses, we may further infer that the 

 gneisses have probably been derived from the granites and 

 might grade into them, although such gradation has not been 

 observed by the writer. 



The Veins and Dikes in the Granites and Gneisses. — The 

 writer regrets not to have had time to examine more closely 

 the veins and dikes of the cerros about Caicara, as a more de- 

 tailed and special study of these would have brought out prob- 

 ably different series of them, so far as strike and dip on the 

 one hand, and composition on the other, are concerned, and the 

 interrelation of these different series might have thrown some 

 light upon the nature and succession of dynamic movements 

 which the gneisses and granites have undergone. As time did 

 not permit this, only specimens were taken and the strike deter- 

 mined of the veins and dikes encountered in ascending the 

 cerros. From notes taken in the field, and from the study of 

 sections prepared from some of the specimens collected, the 

 following may be of interest. 



While the writer is far from attaching any special signifi- 

 cance to it and deducing any particular law of succession from 

 it, because of the limited material at hand, it is nevertheless 

 a peculiar fact that all of the more prominent quartz veins 

 encountered have a strike magnetic .N.-S., while all the peg- 

 matite dikes of the region strike normal to this direction, viz., 

 E.-W. The writer also found near the summit of Cerro de 

 Morano a vein of fine-grained amphibolitic gneiss that varied 

 in thickness from two to three feet. A few feet below the top 

 of Cerro de los Spiritos a felsite dike running E.-W. was met 

 with, about one foot thick and standing out prominently two 

 feet above the surrounding coarse-grained granite, so that from 

 a distance it had the appearance of a wall. Microscopic inves- 

 tigation showed that its main constituents are quartz and plagio- 

 clase in nearly equal proportions, with some brown biotite in 

 shreds and flakes. Also in the dike of pegmatite encountered 

 midway between the foot and the summit of Cerro de Morano, 

 and mentioned above, there are scattered through it a few small 

 flakes of decomposing biotite. It might be mentioned in this 

 connection that the dike cuts the foliation of the gneiss at right 

 angles. Microscopical examination of the quartz veins shows 

 that they are made up of small, interlocked grains of quartz 



