I9I3-] STEVENSON— FORMATION OF COAL BEDS. 39 



essential part of the geologist's equipment. The writer had as his 

 duty, almost 40 years ago, the work of studying in greater detail 

 extensive areas examined 30 years before by pioneer laborers in the 

 northern part of the Appalachian basin. He has never been able to 

 restrain the feeling that the work of those early geologists bordered 

 on the miraculous — the intuition of Hodge, Jackson, Henderson and 

 J. P. Lesley seems to him almost more than human. Even at the 

 time of revision by geologists of the Second Geological Survey of 

 Pennsylvania, the conditions, though better, were poor enough ; de- 

 pendence had still to be placed mostly upon natural sections, for the 

 great mining industry was still in infancy and deep borings for oil 

 were unknown. The defective conceptions inherited from the pre- 

 ceding generation were accepted and continuity of coal beds was 

 taken as the fact, barren areas being regarded as exceptional. This 

 belief was strengthened by the known distribution of the Pittsburgh 

 coal bed, which appeared to have been proved within an area of not 

 far from 15,000 square miles. But the multitude of shafts, the 

 vast number of oil-well records, the increased number of natural 

 exposures due to railway and road construction have provided data 

 during the last twenty-five years, which compel modification of 

 opinion. 



When I. C. White, after study of oil-well records in West Vir- 

 ginia, announced that the Pittsburgh coal is wholly absent from 

 fully one half of the area enclosed within the outcrop, the an- 

 nouncement was received with surprise. Stevenson, nearly twenty 

 years earlier, had reached the conclusion that the Allegheny coal 

 beds, for the most part, were wanting in the interior portion of the 

 bituminous region, but White's study of the well records gave the 

 evidence. There is a continuous area of about 10,000 square miles 

 in which coal accumulation was very irregular from the end of the 

 Pottsville to the close of the Carboniferous. But the irregularity is 

 not confined to the central area ; it is characteristic, to a less extent, 

 of the whole region. 



The conception of continuity was a normal conclusion from the 

 available facts. A coal bed was generally found almost directly 

 under the Mahoning sandstone, resting on a fireclay which overlay 



