108 GEOLOGY OF OHIO. 



present is in large part due to the action of the cause we are now con- 

 templating ; and we are justified in concluding that in these two geol- 

 ogical periods similar causes produced similar effects. 



In Ohio the outcrop of the Carboniferous conglomerate forms a narrow 

 belt, which enters the State from Pennsylvania about the middle of the 

 eastern line of Trumbull county ; the formation having here a thickness 

 of from fifty to sixty feet. Thence it extends in a line from three to five 

 miles in width to the township of Howland ; thence follows along down 

 on either side, or forming the bottom of the valley of the Mahoning to and 

 below Youngstown. Here it is greatly diminished in thickness, varying 

 from six inches to twenty feet, and in some places is even scarcely percep- 

 tible. From the valley of the Mahoning the outcrop of the Conglomer- 

 ate passes north and west through the southern part of Trumbull county, 

 forms the banks of the Mahoning at Newton Palls, thence trends north- 

 ward in a sinuous line through the eastern margins of Portage and 

 Geauga counties, until its northern extension in two or three prominent 

 headlands reaches over the line of Lake county. Little Mountain, near 

 Chardon, is an island of the Conglomerate, and the one which ap- 

 proaches nearest to the Lake, above which it rises to the height of 750 

 feet. From this point the Conglomerate stretches away south and west, 

 occupying a large area, which includes the greater part of the counties of 

 Geauga and Summit, and the north-west corner of Portage. Throughout 

 this region it underlies the highlands drained by the Cuyahoga and 

 Chagrin, reaching out toward the north-west in a great number of prom- 

 ontories and islands, which form the divides between the branches of the 

 streams I have mentioned, and which owe their isolation and relief to 

 the excavation produced by this system of water-courses. The bed of 

 the Cuyahoga lies in the Conglomerate throughout nearly all of its 

 course to Cuyahoga Falls. Here it is cut through by the stream, and 

 the cascades are produced by the water flowing over conglomerate 

 ledges ; thence, to the south line of Cuyahoga county, the Conglomerate 

 forms the summits of the cliff bordering the valley on either side. In 

 all this section of the State it is generally about 100 feet in thickness, 

 being thickest in Parkman and Nelson, where it is 175 feet. It is 

 usually composed of very coarse materials, lying in thick beds. Of these 

 the lowest, with a thickness sometimes of twenty feet, is often a mere 

 mass of pebbles, from half an inch to two or three inches in diameter, 

 with just enough sand to fill the spaces between them. 



South and west of Medina county the area underlaid by the Conglom- 

 erate is narrow, and its thickness is much diminished. In Wayne and 

 Holmes counties it is very irregular, generally thin, and often wholly 



