390 Scientific Intelligence. 
of slate. On the same sheet there is in addition a diagram (200 
identification of the beds of different mines is plainly of very great 
importance in giving a knowledge of what beds may be expected 
Another sheet gives a topographical map of the surface on 
scale of 1600 feet to an inch, half less in scale than the under- 
ground map, and with contour lines every ten feet. 
To give a knowledge of the situation of the basin with reference 
to the whole anthracite region, a sheet is added with a general 
map of the northeastern corner of Pennsylvania, on a scale < 
nearly five miles to an inch, showing all the different fields im 
their relative position. On the same sheet there are eleven col- 
umnar sections, on a scale of 300 feet to an inch, to show the coal 
beds of the different basins and their relation to one another. 
It is striking here how variable is the number of coal beds in the 
different sections and at what variable distances apart. The sheet 
has further a list of the 340 collieries in operation, with their 
yield in 1881, amounting in all to thirty and one-half millions of 
tons. 
_The total annual yield of anthracite year by year from the be- 
ginning is given on a separate sheet, divided, too, in separate 
the kind published for many years by Mr. P. er 
Vith such enormous drafts upon the fixed deposit of coal the 
very weighty question presses forwar w long before the 
ow large the amount of coal is that we are drawing upon 5 
for on the underground map the actual extent of the Mammoth 
Coal Bed and of its comparatively small portions hitherto worked 
out is given, and the HA phic sections show by what thickness 
pite of its inclina- 
tion at different points and even of its overturned condition 1» 
