6 KEMP'S ORE DEPOSITS. 



1.01.03. The rock species themselves are classified into three 

 great groups the Igneous, the Sedimentary, and the Metamor- 

 phic. 



The Igneous (synonymous terms, in whole or in part: mas- 

 sive, eruptive, volcanic, plutonic) include all those which have so- 

 lidified from a state of fusion. They are marked by three types 

 of structure the holo-crystalline, the porphyritic, and the glassy, 

 depending on the circumstances under which they have cooled. 

 Under the first type of structure come the granites, syenites, dio- 

 rites, gabbros, diabases, and peridotites; under the second, quartz- 

 porphyries, rhyolites, porphyries, trachytes, porphyrites, andesites, 

 and basalt; under the third, pitchstone, obsidian, and other glasses. 



The Sedimentary rocks are those which have been deposited in 

 water. They consist chiefly of the fragments of pre-existing rocks 

 and the remains of organisms. They include gravel, conglom- 

 erate, breccia, sandstone, both argillaceous and calcareous, shales, 

 clay, limestone, and coal. In volcanic districts, and especially 

 where the eruptions have been submarine, extensive deposits of 

 volcanic lapilli and fine ejectments have been formed, called tuffs. 

 With the sedimentary rocks we place a few that have originated 

 by the evaporation of solutions, such as rock salt, gypsum, etc. 



The Metamorphic rocks are usually altered and crystallized 

 members of the sedimentary series, but igneous rocks are known to 

 be Subject to like change, especially when in the form of tuffs. 

 They are all more or less Crystalline, more or less distinctly bedded 

 or laminated, of ancient geological age or in disturbed districts. 

 They include gneiss, crystalline schists, quartzite, slate, marble, and 

 serpentine. 



After a brief topographical survey, we shall employ the above 

 terms to summarize the geological structure of the United States. 

 The several purely artificial territorial divisions are made simply 

 for convenience. Nothing but intelligent travel will perfectly ac- 

 quaint one with the topographical and geological structure of the 

 country, and in this connection Macfarlane's " Geological Railway 

 Guide" and a geological map are indispensable. 



1.01.04. On the east we note the great chain of the Appalachi- 

 ans, with a more or less strongly marked plain between it and the 

 sea. This is especially developed in the south, and is now generally 

 called the Coastal Plain. It is of late geological age and contains 

 the pine barrens and seacoast swamps. The Appalachians them- 

 selves consist of many ridges, running on the north into the White 



