Five feet below this,
again, was a third forest with large stumps of Lepidodendra, Calamites, and
other trees.
BLENDING OF COAL-SEAMS.
Both in England and North America seams of coal are occasionally observed to be
parted from each other by layers of clay and sand, and, after they have been
persistent for miles, to come together and blend in one single bed, which is
then found to be equal in the aggregate to the thickness of the several seams. I
was shown by Mr. H.D. Rogers a remarkable example of this in Pennsylvania. In
the Shark Mountain, near Pottsville, in that State, there are thirteen seams of
anthracite coal, some of them more than six feet thick, separated by beds of
white quartzose grit and a conglomerate of quartz pebbles, often of the size of
a hen's egg. Between Pottsville and the Lehigh Summit Mine, seven of these seams
of coal, at first widely separated, are, in the course of several miles, brought
nearer and nearer together by the gradual thinning out of the intervening
coarse-grained strata and their accompanying shales, until at length they
successively unite and form one mass of coal between forty and fifty feet thick,
very pure on the whole, though with a few thin partings of clay.
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