MISSISSIPPIAN-PENNSYLVANIAN UNCONFORMITY 107 



bear evidence of a more or less westerly slope toward the ridge. 

 They are clearly hills bordering a valley, and are conclusive evi- 

 dence of former dissection to a depth of nearly 200 feet. This same 

 hill and valley topography of the Cuyahoga is found all through 

 eastern Trumbull and northern Mahoning counties, with the 

 conglomerate often absent, and with the Sharon coal lying close 

 above the Cuyahoga. 



One of the finest exposures of the unconformity occurs in Mineral 

 Ridge, south of Niles, and near the Mahoning-Trumbull line. 

 A deep east-and-west ravine cuts through a north-and-south 

 Cuyahoga ridge finely exposing the contact, showing the horizontal 

 shale and flaggy layers of the Cuyahoga, overlain by the steeply 

 inclined strata of the Pennsylvanian. The slope of the Cuyahoga 

 is toward the east, and at an angle of about 25 , is ragged or stair- 

 step like, and is directly overlain by 2 or 3 feet of crude, mixed 

 sandstone, without lamination or bedding planes, which grades 

 quickly into a bluish shale, then to a carbonaceous shale which 

 carries the well-known and formerly much- worked bed of iron ore. 

 The ore is a highly ferruginous limestone, which is certainly the 

 Lowellville limestone. Directly above the ore is a bed of coal — 

 the Mineral Ridge coal — which lies only 8 feet above the Cuyahoga. 

 The sandstone, shale, ore, and coal all lie at the same steep angle 

 above the Cuyahoga. 



I have stated above that the Sharon conglomerate bears evi- 

 dence of being a stream deposit. This appears from its position, 

 its constitution, and its structure. In some places it is little else 

 than a mass of quartz pebbles which range in size from coarse sand 

 to half the size of the fist. Commonly the stratum is an alterna- 

 tion of sand beds and pebble layers, of constant variation both 

 horizontally and vertically. Bottom-set, fore-set, and top-set 

 beds are common. The sudden change from sand to gravel, and 

 the very variable structure of the sand beds, all of which may be 

 repeated several times in a single rock face, can be accounted for 

 only by stream action. There is not any feature of the con- 

 glomerate that stream action does not produce. On the other 

 hand, the writer is unable to conceive of any other agency capable 

 of producing a like stratum. 



