NOTES ON THE REGION ABOUT CAICARA, VENEZUELA 245 



The frequent occurrence of a micro-pegmatitic texture suggests 

 conditions in the original magma that favored a simultaneous 

 crystallization of the quartz and feldspar. 



Of the feldspathic minerals those of the soda-lime group appar- 

 ently prevail over the orthoclase (not so much over the microcline), 

 and among them labradorite is the one most frequently found. 



The biotite occurs in lath-shaped crystals and in shreds and 

 flakes, the amphibole mostly with prismatic outlines, and only 

 occasionally in cross-sections. It was in such a cross-section that 

 an intergrowth of biotite and amphibole was observed, the former 

 penetrating the latter, clearly demonstrating their contempo- 

 raneous development. Apatite and titanite occur as inclusions 

 in the biotite, while the amphibole contains apatite and magnetite. 

 Microlites of biotite and apatite needles have been observed in 

 feldspar, while quartz carries magnetite, apatite, and occasionally 

 zircon. In cavities within the quartz liquid inclusions are some- 

 times present. Titanite is also found free in wedge-shaped crys- 

 tals, and considerable garnet, in more or less complete crystals, 

 occurs. Secondary minerals are calcite, which might have been 

 derived from some of the feldspars, and chlorite, which apparently 

 has come from the biotite. 



Wavy extinction in quartz and feldspar; bending, breaking, 

 and slicing of feldspar and biotite; granulation of feldspar and 

 occasionally of quartz; and the complete crushing of titanite 

 crystals strongly suggest dynamic stress and shearing. 



The occurrence of looped grains of orthoclase, and the more or 

 less advanced decomposition and the decoloration of a considerable 

 percentage of the biotite indicate katamorphic action, most prob- 

 ably by descending waters, while the secondary growth of min- 

 erals, involving zonal structure, and the formation of veinlets, 

 where crystals were broken, tell rather of the anamorphic activity 

 of ascending solutions. 



2. THE GNEISSES 



The gneisses of the cerros in the sabana of Caicara comprise 

 those of the Cerro de Caicara, Cerro de Arinoza, with the ex- 

 ception of its base, and those of the Cerro de Morano. A micro- 



