366 KEYES — GRANITES AND PORPHYRIES IN THE EASTERN OZARKS. 



Tabulated, they are as follows : 



r Granite (proper). 



Granular < Granitite. 



(^ Hornblende-granite. 



Granites. 



i 



( Granite-porphyry — phenocrysts 



-r> 1 •+• J feldspathic. 



rorphyritic < r^ -.^ , ■, , 



^ -^ j branite-porpli3''ry — phenocrysts 



i^ quartzose. 



Porphyries 



Granophyric 

 ' Porphyrite. 



Porphyry. . . . 



Ophitic 



Granophyre. 



' Microgranite. 

 J Grano})hyre. 

 I Felsophyre. 

 (^ Vitrophyre. 



( Diabase. 



( Olivine-diabase. 



Dike rocks i Pori.hvrite I diabase porpliyrite 



^ " I Quartz-diabase-porphyrite. 



Glassy I Diabase-porphyrite. 



' '" -^ I Melai)hyre. 



. The subordinate types require no special elaboration in the present 

 connection. All the basic rocks, with a few possible exceptions, occur 

 in narrow dikes and may be also neglected. Only the two leading facies 

 of the acid rocks demand particukir attention. 



LITHOLOGICAL CHARACTERS OF THE GRANITES. 



The granites are rather coarse grained rocks, of a reddish to grayish 

 color. They are almost wholly mixtures of orthoclase and quartz, with 

 a little biotite or hornblende as tlie third essential component. The 

 plagioclase feldspars occur sparingly ; the accessories, magnetite, zircon 

 and apatite, are present only in minute crystals and are not abundant. 

 One of the most striking features in the mineralogical constitution of 

 these rocks is their poverty in the ferromagnesian silicates. 



As a rule the texture approaches the porphyritic and the rock passes 

 into a true granite-porphyry. Phenocrysts an inch or more in lenfjjth 

 are not infrequent in many ])laces. On the other hand the rock becomes 

 fine grained, graduating finally into tyj^ical porphyry. In the porphy- 

 ritic facies of the granite the feldspars make up the greater part of the 

 groundmass. The individuals have so interfered with one another in 



