WESTERN: COAL MEASURES AND INDIANA COAL. 547 
Colonel WHITTLESEY stated that the representations of Central Ameri- 
He could not say, however, how true to the originals the copies were. 
Western Coat MEASURES AND InpIANA Coat. —By PROFESSOR 
Cox. 
Tue study which I have given to the geology of the West, has 
led me to conclude that the Carboniferous rocks embracing the 
coal beds, both of the Appalachian and Western coal fields, were 
formed in two great depressions that gave rise to large inland 
seas. These seas communicated on the south and west with the 
ocean, which then extended far up the Mississippi valley and coy- 
ered most of the southern states as far north as the thirty-fifth 
parallel. 
A high ridge or plateau of Silurian rocks, capped in places 
with the Devonian, and lying in a northeasterly direction across 
the states of Tennessee and Kentucky, and along the western bor- 
der of Ohio and the eastern border of Indiana, separated these 
two seas from each other, and spreading out over the northern por- 
tion of the two latter states, extendéd into Pennsylvania on the 
east, and Illinois and Iowa on the west, forming an almost unbroken 
chain along their northern shores. 
In these seas were formed the Sub-carboniferous rocks, and, as 
the water became shallow from the accumulated sedementary ma- 
terial that went to build them up, a barrier was formed, which 
shut out the ocean and cut off the source of salt water supply. 
Facilitated, also, by the drainage from a large surface area, the 
waters of these seas became less and less brackish, and the condi- 
tions necessary for the accumulation of the coal vegetation were, 
in this way, brought about so gradually that many marine forms 
of life continued to exist and by degrees accommodated them- 
selves to the new condition of things 
That marine forms of life are brought to adapt themselves to 
fresh water habitudes, under favorable conditions, has been shown 
by the researches of Dr. William Stimpson, who found by deep 
dredgings in Lake Michigan, species of marine crustacea in great 
abundance; and similar discoveries had previously been made of 
marine forms of life by dredging in the large fresh water lakes of 
Europe. 
AMER. NATURALIST, VOL. V. 35 
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