196 The A^nerican Geologist. Marci., isss 
The terrace upon which the better portion of Cincinnati is built 
represents one of these enlargements of the lower set of glacial 
terraces. Another appears at Portsmouth, at the mouth of the 
Scioto, and another just below Marietta, at the mouth of 
Muskingum. No other appears in going up the river, until 
reaching the vicinity of Big Beaver creek, which is the first 
stream of importance which comes into the Ohio from the glaci- 
ated region between Marietta and Pittsburgh. The boulderj' ter- 
race at the mouth of the Beaver is about 130 feet above low- 
water mark. 
But the trough of the Ohio has been eroded to a considerable 
depth below its present bottom, and has been filled with gravel, 
in places at any rate, up to the hight of the terraces just men- 
tioned. At Cincinnati the rock bottom is. more than 100 feet 
below the present bottom. The Tuscarawas river and Beaver 
creek have likewise been filled up for more than 100 feet abov« 
their rock bottom. 
The present channel of the Ohio I'iver occupies a comparativel}' 
narrow trough or gorge worn through parallel strata of limestone 
and sandstone to an average depth, estimated from the rock bot- 
tom to the rock shell of the ancient base-level, of about 800 feet. 
The rocky shelf marking this ancient base-level is faiz'ly distinct 
in the whole upper portion of the Ohio and of its tributaries. 
The narrow gorge or trough eroded in it is probably not less than 
1,200 miles long, as the river runs, while the gorges of the tribu- 
taries would almost double the amount. Now the bordering rockj^ 
shelf of the ancient base-level is covered at various places with 
extensive water deposits containing considerable granitic material, 
both in the shape of gravel and small pebbles and occasionally 
of boulders of considerable size. That the water making this 
deposit was iceladen is evident from frequent angular fragments, 
from one to three feet in diameter, which are mingled with the 
finer stratified material. These upper terraces are therefore 
clearly of glacial age. For as there is no granitic material in 
place in the upper Ohio valley, it could onl}- be derived from the 
debris brought by glacial ice into the valley from Canada or the 
Adirondacks. 
The question raised by the facts here summarily stated is 
whether or not this vast erosion of the trough of the Ohio below 
the level of the upper gravel terraces was preglacial or intergla- 
