350 PALEOZOIC SYSTEM OF ROCKS. 



Westphalia 117 seams. The aggregate thickness of all the seams in 

 Lancashire is 150 feet ; in Pottsville, Pennsylvania, 113 feet ; in Western 

 coal-fields, seventy feet ; in Westphalia, 274 feet ; in Mons, 250 feet.* 



The thickest and purest are usually near the middle of the series. 

 Evidently the conditions favorable for the formation and preservation 

 of coal commenced gradually, even back in the Devonian, reached their 

 culmination in the middle Coal-measures, and gradually passed away. 

 This geological day had its morning, its high noon, and its evening. 



Coal Areas of the United States. — In no other country are the coal- 

 fields so extensive as in the United States. The principal coal-fields 

 are shown on map of Eastern United States, on page 291. 



1. Appalachian Goal-Field. — This, the greatest coal-field in the 

 world, commences in Northern Pennsylvania, covers the whole of West- 

 ern Pennsylvania and Eastern Ohio, a large portion of West Virginia 

 and Eastern Kentucky, then passes southward through East Tennessee, 

 touches the northwest corner of Georgia, and ends in Middle Alabama. 

 In general terms, it occupied the western slope of the Appalachian 

 from the confines of New York to Middle Alabama. Its area is at least 

 60,000 square miles. 



2. Central Coal- Field. — This covers the larger portion of Illinois, 

 the southwest portion of Indiana, and the western portion of Kentucky. 

 Its area is about 47,000 square miles. 



3. Western Coal- Field. — This covers the southern portion of Iowa, 

 the northern and western portion of Missouri, the eastern portion of 

 Kansas, and then passes southward through Arkansas, Indian Terri- 

 tory, and into Texas. Its area is estimated at 78,000 square miles. 

 These two coal-fields are seen to be connected by sub- Carboniferous. 

 They are probably one immense field separated by erosion. 



4. Michigan Coal- Field. —hi the very center of the State of Michi- 

 gan there is another coal-field occupying an area of 6,700 square miles. 



5. Rhode Island Coal- Field. —A. small patch of 500 square miles' 

 area is found in Ehode Island, extending a little into Massachusetts. 



6. Nova Scotia and New Brunswick.— -This is a large area on both 

 sides of the Bay of Fundy. It is estimated at 18,000 square miles. ^ 



The following table gives approximately the areas of American 

 coal-fields of the Carboniferous age : 



Appalachian 60,000 



Central 47,000 



Western ^,000 



Michigan 6/700 



Rhode Island 5°0 



192,200 



Nova Scotia ^S, 000 



210,000 



* Nature, vol. xlii, p. 322, 1890. 



