766 GEOLOGY OF OHIO. 
THE UNGLACIATED AREA. 
On passing into the unglaciated portion of the State, the whole 
surface of the country immediately changes its aspect: till suddenly 
ceases to occur; no scratched stones are to be found; granite boulders 
and other transported rocks disappear, except in the valleys of the 
streams. Over the whole of this unglaciated area the streams flow in 
narrow channels cut through the horizontal strata of the coal measures 
and of the Waverly sandstone to a depth of from three hundred to five 
hundred feet, and are everywhere lined by terraces of gravel which are 
far above the present high-water mark. The Ohio River, from far 
below Cincinnati to the head-waters of the Allegheny and Monon- 
gahela rivers, a distance of more than fifteen hundred miles, occupies a 
narrow valley worn by the stream in preglacial times, and was the 
great distributer of the drift brought into it by the streams from the 
north, which all along emerged during the glacial period from the ice- 
front, and which in some places approached to within a few miles of 
the river. Upon the highlands in this unglaciated region the soil is 
shallow, and consists of the remnants of the rocks in places which have 
been disintegrated by sub-aerial agencies. 
As before remarked, in Ohio, and probably further west, the prairie 
region is seen to have been the product of the glacial period. It 
was the moving ice of that period which wore down the prominences 
and filled up the depressions to produce the dead level or gently rolling 
surface of all this prairie region. ‘The action of running streams pro- 
duces fertile intervals in narrow valleys, but the sheet of ice that 
passed over our continent ground up the rocks, and spread the detritus 
over the whole surface. In the glaciated regions of Ohio the soil is 
nearly everywhere fertile. A noticeable quality in the soil of this por- 
tion of the State is the mixture of the elements composing it. All the 
rocks to the north have contributed to its composition. In the soil of 
the glaciated counties there are found the pulverized fragments of 
various granites from Canada and of the local limestones, mingled with 
those of the neighboring shales and sandstones. All these elements 
have been kneaded together into one homogeneous mass by the moving 
ice, as the housewife kneads her flour and yeast together; and the fifty- 
six feet of till, to which we have referred, is as good soil at the bottom 
as at the top. The soil of the glaciated portion of Ohio is absolutely 
inexhaustible. 
