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 Ahorseback. 

 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 tjiree 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 thirteen 

 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. 



Boivlders 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 coalj 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 rounded, 

 and was composed of talcose slate. 



These and similar stones found in the coal I have supposed were enr 

 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 



