86 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



Before following the section into Maryland it may be well to sum- 

 marize the conditions in Pennsylvania. The thoroughly persistent coal 

 beds are the Upper Freeport and Lower Kittanning, both of which attain 

 great commercial importance in several parts of the basin. The others 

 are of irregular occurrence and vary so in the quality of their coal that 

 they are seldom of any importance. The intervals between the beds show 

 great variation in almost contiguous sections, but it is worthy of note 

 that the interval between the two important coal beds, Upper Freeport 

 and Lower Kittanning, shows little variation in any given area. It ex- 

 hibits great regularity as appears from this table: 



Feet 



Snowshoe, Center county (F. Piatt) 172 E. 



Morrisdale, Clearfield county (Chance) 156 W. 



Houtzdale, Clearfield county (I. C. White) 161 W. 



Bennington, Blair county (Fulton) 179 E. 



The same (d'Invilliers) 193 E. 



Sonman, Cambria county 204 E. 



Wilmore, Cambria county (d'Invilliers) 195 E. 



Johnstown, Cambria county (Fulton) 181 W. 



Hooversville, Somerset county (W. G. Piatt) 195 W. 



Castlemans, Somerset county (W. G. Piatt) 200 W. 



The letters refer to the east and west sides of the basin. From Clearfield 

 southward there is evidently an increase in thickness of the measures. 



No limestone is reported on the easterly side of this basin north from 

 Cambria county, where one finds the L T pper Freeport and at 3 or 4 miles 

 farther south the Johnstown cement; but the Lower Freeport occurs on 

 the westerly side as far north as Snowshoe, in Center, and the Johnstown 

 cement is said to be in northern Clearfield. In central and in most of 

 southern Clearfield all limestone is wanting practically, the limestone 

 border evidently skirting the eastern edge. The distribution of the lime- 

 stones geographically is capricious in the extreme, only the Johnstown 

 being reasonably persistent; it is generally found wherever its horizon is 

 exposed. The composition of the limestones is equally variable ; each of 

 them at times is pure enough to yield very fair lime, but they are fre- 

 quently so siliceous or so argillaceous as to be worthless for any purpose, 

 and such changes occur within short distances. None of them is mark- 

 edly fossiliferous ; several contain minute univalve shells, but distinctly 

 marine forms were not seen in any. The Butler, Freeport, Kittanning, 

 and Clarion sandstones are unimportant. The Freeport interval usually 

 contains some sandstone, at times massive, even pebbly, but the other in- 

 tervals are filled for the most part with shale except in Somerset and 

 southern Cambria, where the Clarion is frequently a massive rock. 



