652 GEOLOGY OF OHIO. 
These specimens 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 ting power is certainly greater than 
that of the coal of this territ-y;. 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 ig 1.02 per cent.; in the four specimens of Straitsville coal 0.79 per 
cent. In the Briar Hill coke the average is 0.93 per cent.; in the Straits- 
ville coke 0.172 per cent. 
From a careful study of the whole field, I regard this as an Shiivently 
fair illustration 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- 
eluding 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: 
