ANTHRACITE COAL MEASURES. 243 
geologists, as already stated, are contained in for- 
mations of the period of the graywacke group. 
They extend, according to Professor Rogers, more 
than 42,000 feet in depth. It will be recollected 
that we described three distinct mountain ranges, 
extending through the Middle and Southern States, 
as, 1. The Blue Ridge System on the east; 2. The 
Alleghany on the west ; and between these, 3. The 
Appalachian^ consisting of a wide belt of parallel 
mountain ridges, with deep intervening valleys. 
Now it is the rocks of this region that constitute 
the oldest fossiliferous group of the United States, 
and that contain the anthracite coal ; and because 
they are next in the descending order to those con- 
taining the bituminous coal, they are regarded as 
equivalent to the class of strata in Europe known 
as the graywacke group. But whether they are 
or not is of no great consequence. The anthracite 
coal-fields embraced in these strata, so far as yet 
discovered, lie chiefly to the northeast of the Sus- 
quehanna River. If we trace a parallelogram, one 
line following the Kittatinny or Blue Mountains 
from the Water Gap of the river Lehigh to the Sus- 
quehanna, another from that mountain up that last 
river to its north branch, and a third along the north 
branch and its tributary, the Lackawanna, till we 
reach a point almost due north from the point we 
started from, we shall then enclose nearly all the 
genuine anthracite seams hitherto discovered in 
Pennsylvania. Then, to form a correct idea of the 
situation of the coal, we have only to imagine that 
a set of strata, conglomerates, grits, shales, and thick 
beds of anthracite, were deposited on some wide 
and nearly horizontal plain, and not collected, as ap- 
pears to have occurred with many coal-fields, into 
troughs or basins previously formed. Then con- 
ceive the whole of this level once to have been con- 
verted into an undulating surface of valley, hill, and 
mountain, by some general disturbing canse. We 
