44 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



united with those at the west, anywhere north from Kentucky and 

 he leaves to others to decide if tlicre was at any time a connection 

 farther south. 



Still later/'' after very detailed studies in southwest Pennsylvania, 

 he discussed the question Are coal heds continuous? He describes 

 the Pittsburgh, Waynesburgh, Waynesburgh A and Washington coal 

 beds as practically continuous in the northern portion of the Appa- 

 lachian basin within Ohio, Pennsylvania and West Virginia — that is 

 to say. that they are almost invarial)ly present wherever their horizon 

 is reached. P»ut that is not true of the intermediate beds, wdiich fre- 

 quently are wanting in considerable areas ; yet they are constant in 

 many great spaces of from 100 to i.ooo scjuare miles: he cannot 

 resist the conviction that these beds are not in isolated patches but 

 that for the most part these apparently separate areas are merely 

 parts of a connected whole. The barren spaces mark localities which 

 did not present conditions favorable to accumulation of coal. Res- 

 pecting coal beds older than those of the Upper Coal Measures, he 

 is convinced by the evidence of borings, that all. with possible excep- 

 tion of two, merely fringed the border of the basin. 



Andrews,'" in rendering the final report upon his work in south- 

 eastern Ohio, presented the conclusions respecting formation of coal 

 to which he had been led by his many years study of the Ohio 

 measures. 



The Lower Carboniferous detrital rocks were deposited in shallow 

 water; the sandstones show ripple marks, striae and branches of 

 marine plants (the indefinite Sf^iropliyto)i ) . Some conglomerate 

 appears in the early part of the Coal Measures, but it is confined to 

 the shore side of the basin and disappears eastwardly [toward the 

 center of the basin]. Rocks exhibit ra])id variations laterally; sand- 

 stones pass into shales ; limestones into shales and sandstones. Some 

 marine limestones, formed in shallow' water, indicate, as do the coal 

 beds, pauses in the almost continuous subsidence ; but the great lime- 

 stones of the Upper Measures [Monongahela] are to be considered 

 merely as calcareous muds, for they vary as do the other mud rocks. 



"2(1 Geol. Surv. Penn. Rep. KKK. ITarrisburg, 1878, pp. 283-295, 301-303. 

 "E. B. Andrews. Geol. Survey of Ohio, Vol. I., Part I., Columbus, 1873, 



PP- 345. .347-351. 354, 357. 358. 



44 



