§ 20. carboniferous system of north america. 691 



20. Carboniferous system of North America. — 

 In North America, the carboniferous system is largely 

 developed, and has been ably illustrated by Professors 

 Silliman, Eaton, Hitchcock, and other American geolo- 

 gists. The stone-coal, or anthracite, of Pennsylvania, is 

 associated with conglomerates, sandstones, and argillaceous 

 shale : and the conglomerates are composed of quartz peb- 

 bles like those of our Old Red-sandstone. Deposits of anthra- 

 cite exist in Worcester and in Rhode Island, of which an 

 admirable account has been published by Professor Silliman. 



Extensive coal-fields are found to the west of the Alleghany 

 mountains, towards the Mississippi ; and the base of the whole 

 extent of the plain of that mighty river appears to be carboni- 

 ferous limestone, which extends under the Alleghany moun- 

 tains on the east, and the sand plains on the west, and rests 

 on the granitic rocks of Canada on the north. The upper- 

 most layer of the mountain limestone supports strata of 

 bituminous coal and shale. Iron-stone abounds in these 

 deposits, and mines of lead occur over a district of two 

 hundred square miles, between the Missouri and the Illi- 

 nois.* The principal coal-fields in the United States are the 

 Appalachian, the Illinois, and the Michigan ; the Appa- 

 lachian is 720 miles long, and, in many parts, 180 wide: that 

 of the Illinois is nearly as large as England in extent. 



The Appalachian coal-field, before its original limits were 

 reduced by denudation, is computed, by Mr. Lyell, to have 

 been 900 miles long and 200 wide. The thickness of the 

 carboniferous strata in Virginia and Western Penn- 

 sylvania exceeds 3,000 feet.f A large portion of the 

 coal is in the state of anthracite, or stone-coal, resulting 

 from the influence of high temperature. For the most, the 

 bituminous coal is that which is farthest removed from the 

 axis of the greatest disturbance, and where the strata have 



* Smart's Travels in the United States, 

 f Professor H. D. Rogers' Address, May 1844. 

 VOL. II. Z Z 



