of the Ohio Coal-measures. 



197 



the Virginias, and if only the Ohio series were to be classified, 

 it is not probable that the divisions would have been made. 

 But they stand for great and conspicuous facts elsewhere, and 

 it probably would have been better to have maintained them 

 in our territory also. The separation will be recognized in this 

 review."* 



The same classification was used by Dr. Orton in his last 

 report of the Ohio ■ Survey, f which also contained a chapter on 

 "The Coal Fields of Ohio" in which he described the coal 

 seams of the Conglomerate Coal-measures, the Lower Coal- 

 measures and the Upper Productive Measures.;}; 



The Maryland Geological Survey has carefully considered 

 the Carboniferous formations and adopted the classification 

 shown in the following table, which gives the approximate 

 thickness and composition of the formations as exposed in 

 Georges Creek valley in the western part of Allegany county : 



Georges Creek, Md., Section of the Coal-measures and Permian. 



Dunkard 



400'. 



Monongahela 

 250'. 



Conemaugh 

 About 650'. 



400' 



2' — 

 116'± 



100' — 

 115' 



14'± 



144' 

 9' 

 72' 



1' 



! Mainly argillaceous shales, some thin 

 limestones and sandstones and an 

 occasional thin layer of coal. 

 Waynesburg (Koontz) coal. 



Shales and limestones. 



Sewickley (Tyson) coal and shale. 



Mainly argillaceous shales. 



Pittsburg (Elkgarden) or "Fourteen- 

 foot " coal. 



Black and gray shales and thin sand- 

 stones. 



Franklin (Dirty nine-foot) coal, partly 

 shale. 



Shales and sandstones. 

 About one foot of coal. 



*Ibid., p. 43. 



+ Ibid., vol. vii, 1893, pp. 4, 36, 31 and "Geological Scale of Ohio" facing p. 4. 



i Ibid., pp. 255-291. 



