Ashbui-Der.J ^^^ [March 18, 



topography ; where the composition of the bed is most similar, as at Tan- 

 nerdale, Roberts' lot and St. Mary's, it requires all the skill and judgment 

 of a trained geologist to determine their geological relationship. 



In the east mine of St. Mary's Coal Company the roof is found to change 

 suddenly from a black slate to a hard, massive sandstone. The same thing 

 is reported to have occurred in the now abandoned Keystone mine. 



Conclusion. — In view of these facts as regards the variation of the com- 

 position of the Dagus or Kittanning Lower coal bed and the changes which 

 are liable to occur in the associated strata within a small area, similar 

 differences at localities so far removed from one another as St. Mary's, 

 Centerville and Roberts' lot, can certainly have but little weight in deter- 

 mining the relative position of the beds. 



The best and most reliable means of ascertaining the connection existing 

 between distant rock sections is, by making a comparative study of sections 

 in their entirety. A marked similarity will oftentimes be found to exist 

 between the general structure of each section, even where no persistency 

 of character is found to exist between the minor features. 



Clermont Group. — The Clermont* or Ferriferous limestone has a distinct 

 and well recognized representative in the vicinity of St. Mary's. The hori- 

 zon of the limestone is 30 feet above the Clermont or Clarion coal bed. As 

 has been said, pieces of the stone were found along its outci'opping level on 

 the hill north-west of the town. 



In a railroad cutting two miles north-east of St. Mary's station, and ex- 

 tending from mile-post 130 to 130+500 feet, is found exposed the representa- 

 tive of the Ferriferous limestone. It consists of gray and black shale and 

 slate containing bands a few inches thick of limestone and lime balls, 

 heavily charged with iron. No limestone has ever been found in the 

 Fourth Basin north-east of St. Mary's. 



The Clermont or Clarion coal bed (stratum 15), marks the top of the 

 Carboniferous or Pottsville Conglomerate, No. XII. This is the po- 

 sition usually occupied by the Brookville coal bed, but I failed to recognize 

 its representative any where within my district of four counties. The best 

 illustrations and discussion of the variations of the Clarion and Brookville 

 coal beds and of the underlying Homewood or Kinzua creek sandstone 

 may be found in the Clarion county report by Dr. H. Martyn Chance. 



Alton Group. — The position, extent of area and character of the Clermont 

 and Alton group coals is a matter of considerable importance to the coal 

 interests centered about St. Mary's. No geological report can settle the 

 question in a practical way. That the coal beds should exist, if the strata 

 were perfectly regular, I can positively assert ; that they do not exist at every 

 point, has been practically proven. The strata are liable to change, and it 

 must be left to explorations of the di-ift, the drill-hole and the shaft, to test 

 practically the economical value of these coal beds. 



* Clermont is a local geographical name which I gave to this limestone in Mc- 

 Kean and Elk counties, its use was only adopted provisionally until its identity 

 with the Ferriferous limestone of Western Pennsylvania should have been placed 

 beyond a doubt. 



