318 The American Geologist. May, 189) 
average of the Black Creek coal given by the State geological 
survey. From a mean of six measurements of its thickness the 
latter was taken as 2 feet 2 inches, but it has a higher thin seam 
separated by a parting of shale varying in extent from a few 
inches to 17 feet, and as this small seam only reaches about one 
foot in thickness it has not been considered here, but in some 
cases will enhance the value of the coal product. 
Taking (of the lower seam just mentioned) the above data, 
there will be found an average of 3,798 tons of this coal per 
acre of the ground which it underlies. 
The "Black Creek" seam, or the first valuable seam imme- 
diately above it, averages 2 feet 6 inches in thickness, and has a 
specific gravity of 1.362. There are, therefore, 217.15 pounds 
of this coal under every square foot of surface covering it, or 
4,728 tons of 2,000 pounds to the acre. This is a most valuable 
coal for coking, and is the only one which on account of its free- 
dom from impurities is adapted to coke making without previous- 
washing. * An analysis of it given in the State report for 1886 > 
p. 302. shows : 
Moisture 1.36 
Volatile matter 31.79 
Fixed carbon 64.71 
Ash 0.82 
Sulphur 0.32 
Its specific gravity- (1.29) as given with this analysis is a little 
less than my own experiment made it. but this will not very mater- 
ially alter the figure representing the number of tons to every acre 
underlain by it. This figure is on my own data 4,728 tons of 
2,000 pounds. 
The Jefferson seam is the next valuable deposit above the fore- 
going. 
An analysis of it taken from a long exposed heading where its 
best showing would not be expected, gave me the following re- 
sults : 
The coal dried 
at 105° Cent. 
Volatile matter 28.73 
Fixed carbon ' 64.57 
Asli 6.70 
Sulphur 2.82 
Phosphorus 0.001 
*See Note IV. at the end. 
