The Natural History of Chautauqua 



c. Organic Rocks: 



Most Limestones carbonate of lime, made of shells, etc. 

 Dolomite magnesian carbonate of lime. 

 Coal made of plant remains. 



3. THE IGNEOUS ROCKS. 



a. Coarse-grained : 



Granite quartz, orthoclase feldspar, and hornblende or mica, or both. 

 Syenite orthoclase feldspar, and either mica or hornblende, or both. 

 Diorite plagioclase feldspar, and either mica or hornblende, or both. 



b. Either fine- or coarse-grained: 

 Diabase plagioclase feldspar and augite. 



c. Fine-grained: 



Rhyolite quartz, orthoclase feldspar, and hornblende or mica, or both. 

 Trachyte orthoclase feldspar, and hornblende or mica, or both. 

 Andesite plagioclase feldspar, and either hornblende, mica, augite, or 



two of these. 

 Basalt plagioclase feldspar and augite ; often with other minerals. 



4. THE METAMORPHIC ROCKS. 



Name 

 Quartzite. 

 Slate. 



Marble. 



Anthracite. 



Schist. 



Gneiss. 



Source 



Altered sandstone. 

 Altered clay rock. 



Altered limestone. 

 Altered coal. 

 Altered from various 



rocks. 

 Altered from various 



rocks. 



Mineral Composition 



Quartz. 



Partially crystallized 



micaceous particles. 

 Calcite. 



Mainly carbon. 

 Variable. 



Variable ; gneiss and 

 schist usually contain 

 two or more of the 

 following: feldspar, 

 quartz, hornblende, 



5. A TABLE OF GEOLOGICAL TIME. 



Showing the great epochs in the evolution of life upon the earth ; modern 

 time is at the top of the list. 



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