WARREN. — ALKALI-GRANITES AND PORPHYRIES. 



263 



Dark, AIJcaU-FvIdspar- or Rhombcn porphyry. 



This rock is the one to which Professor Crosl)y apphed the name 

 "basic-porphyry." While the rock is distinctly darker in color and 

 suggests a basic rock in its general appearance, and in fact, is truly 

 more basic than the other rocks of the area, it is not a particularly 

 basic rock containing in any case not much under 60% of silica. The 

 term "rhombenporphyry," which will be used here in describing 

 this rock, seemed an appropriate one on account of the "rhomben" 

 habit of the feldspar phenocrysts, and also, on account of the strong 



3 c ale '/y' a^vnf 



\-^ + + I C ranite . 



^'•"^♦I Fine-Gramte. 



olaie. 



I -yi',\\ Grnnite-Porp^xjry. ^S T^C-p. 



Section through the Northern Part of the Pine Hill Area. 



This section is intended to illustrate the relations of the intrusive rocks 

 against the intruded slate where the latter formed relatively deep projections 

 into the igneous mass (deep contact levels). The rhombenporphyry and slate 

 masses have been somewhat exaggerated as to size in order to show them to 

 better advantage. The section is however based on the outcrops as shown on 

 the special map of this area. 



resemblance of the rock, particularly in its microscopic characters, 

 to certain rather fine-grained and somewhat altered rhombenpor- 

 phyries which the writer had examined from the Laurvik region in 

 Norway. The typical rhombenporphyry, it is true, is characterized 

 by much larger phenocrysts and differs chemically from the present 

 rock in some respects. 



This porphyry, as held by Crosby, ^^ is a marginal differentiate of 



39 op. cit., pp. 370-371. 



