White.) 200 [Dec. 17, 



up to the base of the Sharon coal, and in the absence of that deposit, also 

 extend to the very base of the Lower Gonnoquenessing Sandstone which 

 then becomes the base of the Conglo^nerate series. 



Thus it is that in passing south along the Shenango and Mahoming 

 rivers into Lawrence county, the Cui/ahoga shale, and its fossils, are found 

 coming up to the base of the Lower Counoquenessing Sandstone. 



It follows from this northward distribution of the Sharon Conglomerate, 

 that the marine conditions that had so widely prevailed during the closing 

 period of the Subcarboniferous epoch, so far as Western Pennsylvania is 

 concerned, came to an end sooner around the northern margin of the pres- 

 ent coal field than elsewhere, that to the south, marine conditions continued 

 to prevail, while on the northern beaches, brought above or near sea-level 

 either by greater rising or less rapid subsidence, the Sharon Conglomerate 

 commenced to accumulate, and continued to do so during the long time that 

 marine conditions still obtained to the southward ; finally however the in- 

 cursion of the coarse sediments of the Counoquenessing Sandstone destroyed 

 the life in the shallow seas southward, and so far as we know this put an 

 end to Subcarboniferous life and conditions in Western Pennsylvania, that 

 had already been forced a considerable distance southward by the incur- 

 sion of the disturbing currents which carried the coarse material of the 

 Sharon Conglomerate. It may even have happened that still farther south 

 along the Chestnut Ridge region where subsidence was greater, that the 

 marine conditions of the Subcarboniferous epoch continued to exist until 

 the great incursion of coarse sediment which formed the Ilomeinood Sand- 

 stone and completed the Conglomerate series, and this indeed seems in some 

 regions to have actually been the state of affairs since in Fa3'^ette and West- 

 moreland counties. Pa., and in the adjoining county of Monongalia, W. 

 Va., the only member of the series present in any force is the Upper, or 

 HomeiDOod, and it is 175'-200' thick. There is nothing at all to represent 

 the Sharon Conglomerate of the north, and the interval between the TJm- 

 bral Limestone and the Hometoood Sandstone is made up of reddish and 

 greenish shales interstratified with green sandstones which look more like 

 Subcarboniferous rocks than any representatives of No. XII that I have 

 ever seen. And in fact at times this Homewood Sandstone itself appears 

 absent or in little force, and then the red ^shales of the Umbral continue 

 up to the very base of the Lomer Productive Coal measures. 



Hence, if am correct in this interpretation of facts, it will not do to draw 

 a hard and fast line at any place in the series and say that every thing above 

 it is Carboniferous and everything below Subcarboniferous ; for as well as 

 we can unravel the historj^ in Western Pennsylvania, it would seem that 

 the Sharon Conglomerate at least, Avas in process of formation and syn- 

 chronous with marine conditions prevailing farther south, essentially simi- 

 lar to what had existed at the north previous to the change in conditions 

 which rendered the accumulation of that mass of coarse sediment possible, 

 and that subsequently the changed conditions at the north were carried 

 farther and farther south with each great incursion of coarse material until 



