306 GEOLOGY. 



Primary Rocks.* 



The number of primary rocks commonly observed 

 in nature are eight. 



1. Granite which is composed of quartz, fel- 

 spar, and mica. When these bodies are arranged in 

 regular layers in the rock, it is often called gneiss. 



2. Micaceous Schistus. This is composed of 

 quartz and mica, arranged in layers, which are usually 

 curvilinear. 



3. Sienite (or Syenite). Consisting of the sub- 

 stance called hornblende and felspar. 



4. Serpentine. This is composed of felspar, and 

 a body named resplendent hornblende, and their se- 

 parate crystals are often so small as to give the stone 

 an uniform appearance. This rock abounds in veins 

 of a substance named steatite, or soap rock. 



5. Porphyry. Consists of crystals of felspar em- 

 bedded in the same material, but usually of a different 

 colour. 



6. Granular Marble. Consisting of crystals of 

 carbonate of lime, and which, when its colour is white 

 and texture fine, is the material used by statuaries. 



7. Chlorite Schist. This is composed of chlorite, 

 a green or gray substance, somewhat analogous to 

 felspar and mica. 



8. Quartzoze Rocks. Consisting of quartz in a 

 granular form, sometimes united to small quantities 

 of crystalline elements, which have been mentioned 

 as belonging to other rocks. 



* Geology being still in its infancy, and progressive, the early 

 systematic arrangements must necessarily undergo many modifi- 

 cations, until the science approaches nearer to perfection, and 

 its nomenclature acquires greater stability. This will account 

 for an apparent obscurity and confusion in some of the defini- 

 tions, which are disputed and maintained by different theorists ; 

 still they will furnish the reader with a general notion of the 

 meaning attached to them, which in a work of this nature is all 

 that is wanted. 





