136 GEOLOGY OF OHIO. 
have been made by Prof. J. J. Stevenson. It is now established that 
the coal vegetation grew where we find it. A coal seam is literally a 
buried swamp, a fossil peatbog. The facts illustrating this mode of 
origin, for the Sharon coal in particular, have been set forth with great 
clearness by Newberry in his reports upon that seam. But.there are 
equally convincing facts in regard to many of the other seams, all of 
the, proofs, for example, that the sea was near at hand while these seams 
were growing. 
It is not an uncommon thing to find a coarse sandstone, and some- 
times a decided conglomerate, directly overlying a seam of coal. But 
strong currents would be required for the transport of this kind of 
material, and such as belong to the sea. 
The Mercer coals, the Brookville coal in part of its Ohio develop- 
ment, and the Upper Clarion coal are all covered by marine limestones, 
charged with the various forms of the life of the Carboniferous seas. 
These limestones very often come directly down upon the coal, 
making the roof of the seam. ‘These facts certainly show that the sea 
was near at hand when the slight depression occurred that terminated 
the growth of the coal swamp. 
) 
So also the presence of bowlders in the coal requires the neighbor- 
hood of the sea to account forthem. There is in the Geological Museum 
of the State University, at Columbus, a bowlder of metamorphic sand- 
stone, apparently derived from the Cambrian rocks of the Appalachian 
border to the southward, that was taken from the thick coal at Shawnee, 
just above the second slate. The coal was normal in all respects above 
it. The bowlder weighs not less than 200 lbs. The surface of the 
bowlder appears glaciated, and ice transport would seem almost a neces- 
sity for such a block. But this would imply the near presence of the 
sea. The occurrence of bowlders in the body of the coal is rare, but 
there are several instances on record in Ohio geology. (See Report of 
Progress, 1870, p. 78.) | 
The Freeport coals seem to have had a somewhat different history. 
Their limestones, as has been already stated, are not distinctively 
marine. They probably originated in fresh or at least in brackish 
water. They are charged with but one constant and characteristic 
fossil, and that is the almost microscopic form spirorbis. They may 
well be termed spirorbis limestones. But all the facts point to a fresh- 
water rather than to a marine origin for this fossil. 
