488 _ The American Naturalist. [June, 
A GLACIAL ICE DAM AND A LIMIT TO THE ICE 
SHEET IN CENTRAL OHIO. ~ 
By W. G. TicHt. 
The great continental glacier of the Plistocene will ever 
present many interesting problems to the student of those 
times. Its effects may be grouped under two heads; first, the 
general and widespread results of glacial action, and second, 
the local and minor effects produced by the action of local. 
forces. 
Believing that a careful study of these limited phenomena 
will help to illustrate some of the larger problems and enable 
us to gain a better understanding of the geological history of 
Plistocene times, the liberty is taken to present a few points 
of surface geology of a very limited region. Itis hoped, how- 
ever, that the accompanying map and sections will prove of 
interest. 
Licking County lies near the center of Ohio, and is drained 
by the Licking River, which is formed at Newark by the con- 7 
fluence of three streams, The North and South Forks and 
Raccoon Creek. These streams form a hydrographic basin 
which is very nearly co-extensive with the county lines. The 
Raccoon Creek and North Fork rise in the western and north- 
ern portions, which are rather high lands; they flow through 
broad and open valleys, ranging from one-half to one mile 1n 
width, between the Waverly hills. 
The valleys are filled with drift to a depth of 100 to 150 feet, 
increasing in depth toward their lower portions until at New 
ark the gas well borings show a valley filling of over 300 pie 
These two streams are of rapid fall, ascending 250 to 350 fee : 
in the 40 to 50 miles of their lengths. 
The South Fork rises on high ground in the south-west 
portion of the county, flows south and east to near the Lic 
ing Reservoir, which lies about 125 feet above Newark, from 
this point the watercourse is almost due north to Newark. 
