NOTES ON THE REGION ABOUT CAICARA, VENEZUELA 247 



The gneisses, even more than the granites, exhibit overwhelm- 

 ing evidence of metamorphism ; during, as well as since, their 

 formation. Among the evidences of "stress and shearing, may be 

 mentioned: The wavy extinction in quartz and feldspar grains; 

 the bending of biotite; the differential bending and anastomosing 

 of the lamellae of feldspars ; cracks and fractures parallel or normal 

 to the plane of parting in biotite; the slicing of crystals of peg- 

 matite and microcline; the breaking of crystals of feldspar and 

 biotite and displacement of the broken parts by miniature fault- 

 ing; a granulation zone about grains of pegmatite. 



A gneissoid texture is given to the rock by the more or less 

 parallel arrangement of the longer axes of the minerals to the plane 

 of schistosity of the rock. 



The dissolving agency of descending waters is shown by the 

 schiller structure of some plagioclases, the cloudy appearance of 

 other feldspars, and the decomposition of some of the magnetite, 

 biotite, and hornblende. The anamorphic agency of ascending 

 waters is indicated by secondary growth of quartz, plagioclase, 

 and biotite; by the cementing of cracks and fissures, and by the 

 formation of veinlets by segregation from the same mineral or by 

 infiltration from some other source. 



3. THE VEINS AND DIKES IN THE GRANITES AND GNEISSES 



The writer profoundly regrets that he , did not have time to 

 examine more closely the veins and dikes of the cerros about 

 Caicara, as a more detailed and special study of these veins and 

 dikes most probably would have brought out different sets, as 

 indicated by uniformity of strike and dip and of composition, 

 and might have shown something in relation to the nature and the 

 succession of the dynamic movements which the gneisses and the 

 granites, individually or together, have undergone. 



While the writer is far from attaching any special significance 

 to it and deducing any particular law of succession from it, because 

 of the limited material on hand, it is nevertheless a peculiar fact 

 that all of the more prominent quartz veins and dikes encountered 

 have a strike magnetic N.-S., while all the pegmatite veins and 

 dikes strike E.-W. Near the summit of Cerro de Morano a vein 



