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 Falls, 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 ina 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 les 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 Cornglom- 
erate is narrow, and its thickness is much diminished. In Wayne and 
Holmes counties it is very irregular, generally thin, and often wholly 
