I9I2.] STEVENSON— THE FORMATION OF COAL BEDS. 425 



Ohio, while at the south it reached the western boundary of Ala- 

 bama. The area of deposit at that time embraced not less than 

 200,000 square miles. The present outcrop approaches the western 

 border at a few localities in Ohio and Kentucky as well as in 

 Alabama, but for the most part it is two score or more miles east 

 from the original limit. The eastern border is approached in the 

 southern anthracite field of Pennsylvania and apparently it was not 

 far eastward from the Pocahontas outcrop in Virginia ; in Alabama, 

 the eastern outcrop is not more than 25 miles from the original 

 border on that side. But, in most of the space north from Alabama, 

 the present continuous outcrop is from 30 to 100 miles west from 

 that border as it probably existed at the close of the Pottsville. 

 The Appalachian field included a small part of New York, more 

 than two thirds of Pennsylvania, the western third of Maryland, 

 nearly the whole of West Virginia, the eastern third of Ohio and 

 Kentucky, with southwestern Virginia, eastern Tennessee, the 

 northern half of Alabama as well as northwestern Georgia. Here 

 then is an area of sufficient extent to provide ample illustration of 

 purely local features and their relations to the effects of widely act- 

 ing agents. , 



— ^ 



The Appalachian Basin. 

 The Appalachian basin, from its origin to the close of the 

 Palaeozoic, was the scene of frequent changes in the relations of 

 land and water. Schuchert and Ulrich^ have shown that such 

 changes were merely commonplaces in the earlier periods. Those 

 students are not in agreement respecting several matters, which have 

 much interest from a philosophical standpoint, but they are in full 

 agreement respecting all matters which concern the questions at 

 issue here. As Schuchert has shown, the Appalachian basin 

 originally was continuous with the broad Mississippi region and 

 much of it was covered with sea. Toward the close of the Ordo- 

 vician the Taconic revolution began, which, at the east, widened 



^C. Schuchert, "Palaeography of North America," Bull. Geo!. Soc. 

 Amer., Vol. 20, 1910, pp. 427-606; E. O. Ulrich, "Revision of the Paleozoic 

 Systems," ibid., Vol. 22, 191 1, pp. 281-680. 



