270 T. A. Bendrat — Bocks of Cerro de Santa Ana. 



phyry was traced to an elevation of 2550 feet to the foot of 

 the last steep cliff. At this point the mountain culminates in 

 a pinnacle or " horn," as may be seen in the accompanying 

 figures, and attains a height of 2975 feet above sea-level. The 

 pinnacle is composed of a different rock from the porphyry 

 below, in that it is a hornblende diorite of fine to medium- 

 grained texture without phenocrysts, which weathers to a dark 

 chocolate-brown, and exhibits on freshly broken surfaces a 

 bluish gray color, and is penetrated by an intricate system of 

 veinlets. It has a very uneven fracture which makes the pin- 

 nacle extremely rugged, and its ascent very difficult. On 



Fig. 2. 



Cexto de So-nto-A 



r>a. 



Cctto 7fo<(fa 



mn JDioifte. 



prji Hornblende Voifxhyiv ■ 



&ra Diabase. 



_ZW*/Ve 



j&'/<? metZ-r s . 



Figs. 1, 2. The diagrams of figs. 1 and 2 were taken with Dr. W. Sievers' 

 permission from the latter's work : " Zweite Eeise in Venezuela, 1892-93 " ; 

 the geology has been introduced by the writer. 



account of its different texture the writer is inclined to believe 

 that it is a still younger intrusive which invaded both the dia- 

 base and the hornblende porphyry. 



Petrography. 



Diabase. — This is an aphanitic rock which in thin section 

 under the microscope is seen to be composed of augite, olivine 

 and plagioclase and is holocrystalline. Of the minerals plagio- 

 clase is predominant, olivine less so, while the amount of 

 augite is relatively small. The section shows an even, granular 

 groundmass of these three minerals, in which occur, scattered 

 larger, more or less allotriomorphic crystals of plagioclase. 



