OCCURRENCE OF COAL WITH UNUSUAL CONDITIONS 325 
accumulations extended for considerable distances along the front 
of the sand deposit but only to a width of a few feet, and were 
intertongued with and accumulated simultaneously with the adja- 
cent sandstones; that each deposit of coal mud in course of time 
was covered and its growth checked by the advancing sands while 
a new one formed a few feet beyond at the new edge of the sand, to 
be later covered in turn; that after the whole series had accumu- 
lated, the organic mud was compressed in the process of coal 
formation until its thickness was only about one-fifteenth its 
original thickness, and that the readjustment necessitated in the 
surrounding sediments by such local contraction was accommodated 
largely by the soft shales underlying the coal and sandstone. 
It is worth while, also, to call attention to the general conditions 
at the time of formation of the deposit. The marine limestone, a 
few feet below the coal, is known to persist over two or three adja- 
cent counties, and, if properly identified as the Lower Mercer, it 
extends over much of eastern Ohio and northwestern Pennsylvania. 
It marks a period of cessation from deposition of the sandstones 
and shales, with coals, which constitute most of the Coal-measures, 
and which, when fossiliferous at all, are only plant-bearing; it 
marks the prevalence of marine conditions over a large part of the 
northern Appalachian coal basin. The uniform thickness and 
character of this limestone bed indicate that it is the result of an 
abrupt subsidence which dropped the entire area far enough below 
sea-level to give open marine conditions. The phenomena caused 
by transgression and regression, resultant on a slow subsidence 
from above sea-level, appear to be entirely lacking. That open 
marine conditions, probably in shallow water, prevailed, is shown 
by the diversity of marine life forms present and the abundance of 
species and individuals which is commonly found, in central Ohio 
at least, at this horizon. 
The limestone is succeeded abruptly in central Ohio by gray 
argillaceous shales between to and 20 feet in thickness—the shale 
below the coal seam under discussion. These quite commonly 
carry a marine fauna in their lower part. How rich this fauna 
is, is shown by the presence of 57 species from the shale at this 
locality in the collection of the writer’s father, Mr. Eber Hyde. This 
