1912.] STEVENSON— THE FORMATION OF COAL BEDS. 479 



At the beginning of the Conemaugh, one finds on the eastern 

 and northern parts of the bituminous region an important sandstone, 

 which becomes unimportant on the western outcrop in Ohio. In 

 several counties within the Central area, its place is occupied by red 

 shale. The same material occurs in occasional borings farther north 

 near the Pennsylvania line and thin streaks are reported in a few- 

 wells north from that line; but these occurrences seem to be isolated. 

 As one rises in the Conemaugh, he finds the areas increasing, for 

 widely extended deposits appear below the Cambridge, the first per- 

 sistent limestone of the Conemaugh. At this horizon the reds, 

 though variable, are thick in some portions of the Central area and 

 very irregular in others ; but conditions favoring deposition of reds 

 existed at many localities, somewhat widely separated ; such deposits 

 are reported from the Central area; from Ohio at lOO miles toward 

 the west; from the northern counties of West Virginia ; from several 

 counties in southwestern Pennsylvania as well as from Webster 

 county of West Virginia on the eastern outcrop. Away from the 

 Central area, most of the deposits are thin, apparently of small area ; 

 their interrelations cannot be ascertained but there is no doubt that 

 many of them were wholly isolated. They suffice to show that, 

 prior to the formation of the marine Cambridge limestone, conditions 

 favorable to deposition of red shales existed at very many localities 

 within an area of not less than 10,000 square miles. 



The Pittsburgh reds of I. C. White underlie the Ames limestone, 

 which carries a marine fauna and is midway in the Conemaugh. This 

 interval between the two marine limestones is marked by the greatest 

 expansion of reds within the Appalachian basin. No trace of the 

 deposit is seen on the eastern side of the bituminous region except 

 in a small space within western Maryland and the adjacent part of 

 Pennsylvania. Aside from that locality it seems to be absent along 

 the eastern outcrop in Pennsylvania and West Virginia as well as 

 along the western outcrop in Ohio. But in the interior portion of 

 the bituminous region the Pittsburgh reds are present from Boyd 

 county of Kentucky to the northern outcrop, a distance of 275 miles, 

 and the width at times is 80 miles, giving an area of certainly not 

 less than 17,000 square miles. The thickness varies; it becomes 

 almost 250 feet in some localities, when the mass is continuous below 



