652 GEOLOGY OF OHIO. 



These speciia,ens were carefully selected, and represent the best grades 

 of the Briar Hill or No. 1. coal, in the Mahoning Valley. 



They contain an average lower per cent, of water, and a greater per 

 cent, of fixed carbon, and their he iing power is certainly greater than 

 that of the coal of this territ''^/. While in respect to the amount of 

 sulphur contained, the Great Vein coal has the advantage. 



The average amount of sulphur in the six selected specimens of Briar 

 Hill is 1.02 per cent. ; in the four specimens of Straitsville coal 0.79 per 

 cent. In the Briar Hill coke the average is 0.9') per cent. ; in the Straita- 

 ville coke 0.172 per cent. 



From a careful study of the whole field, I regard this as an eminently 

 fair illusti-ation of the comparative value of these two coals. It should 

 be added that coal No. 1 is never persistent over large areas, and often 

 changes abruptly its character both in respect to the thickness of the bed 

 and the amount of impurities. The Great Vein coal of this field is un- 

 usually persistent, having only one or two lines of erosion through it, 

 from the points of maximum thickness, thinning in all directions very 

 gradually, and no where abruptly acquiring peculiarities that interfere 

 with its value. While the field is remarkable for the persistency of this 

 coal, it is almost equally remarkable for the want of continuity, and the 

 irregularities in its other mineral deposits. The few members of the 

 series which are substantially continuous, vary much in their character 

 and thickness, and the intervals between them, and the nature of the in- 

 cluding rocks is constantly changing. 



The following is a general section of the rock strata in the Straitsville 

 and Shawnee region, extending northward to McCuneville, and supple- 

 mented by the strata disclosed in boring for salt at that place : 



