174 GEOLOGY OF OHIO. 
did not carry sand, the channel was filled with a finer sediment, now 
forming shale or fire-clay. 
Sometimes a sheet of rock is encountered in working a coal seam, 
which evidently consists of material washed into a fissure that was at one 
time opened through the coal and associated strata. Where this mate- 
rial was sand, we now find a wall of sandstone—perhaps a foot or more 
in thickness—and this is also, though improperly, called a horseback. 
Where clay was deposited in the fissure, this forms what is known as a 
“clay seam,” a troublesome but not serious impediment in mining. As 
might be expected, these sheets of clay and stone very frequently occupy 
the space between the walls of a fault. 
Duplication of Coal Seams.—We occasionally hear of a coal seam sud- 
denly swelling to two or three times its normal thickness. ‘Two marked 
instances of this kind have come under my observation. Both of these 
are in Coal No. 5, in Tuscarawas county—one in the mine of Mr. Holden, 
at Mineral Point, the other on the lands of the Zoar Community, two 
miles west of the village of Zoar, and five miles distant from the first- 
mentioned locality. The normal thickness of Coal No. 5 in this region 
is three and a half to four feet, but along the line of disturbance it is 
found to be entirely removed over a narrow belt, and on the south side of 
this it is thickened to nine or ten, and even, in one place, to thirtcen 
feet. Here it is plain that the phenomena were produced by lateral pres- 
sure, by which the coal was slipped from the fire-clay and pushed over 
on to an adjacent belt, where it is, of course, doubled in thickness. 
These interesting cases will be described more in detail in the report on 
Tuscarawas county. 
Bowlders in Coal Seams.—Quite a number of bowlders of rock foreign 
to the localities where found have been met with in the coal seams of 
Ohio. One of these is mentioned by Prof. Andrews in the Report of 
Progress for 1870, p. 78. It was a rounded bowlder of quartzite, seven- 
teen inches in its longer and twelve inches in its shorter diameter, and 
was found partially imbedded in the surface of the Nelsonville coal, at 
Zaleski. Another bowlder was found by myself in the blackband iron ore, 
which forms a parting in Coal No. 1, at Mineral Ridge, Mahoning coun- 
ty. This was some four inches in diameter, angular, and not pounce, 
and was composed of talcose slate. 
These and similar stones found in the coal I have supposed were en- | 
tangled in the roots of trees, and thus floated and dropped. The black- 
band ore which contained the bowlder found in Mahoning county is 
simply a highly ferruginous, bituminous shale or cannel, which marks a 
local and temporary submergence of the marsh where Coal No. 1 was 
