I'errace Deposits of the Jfonouf/ahela lliver. — White. 369 
which I have named lake Monongahela. The writer has often 
called the attention of geologists to a remarkable old gap in 
the divide which now separates the Ohio and Monongahela 
waters, at the head of the latter stream, just west of Salem, 
on the Baltimore and Ohio Southwestern E. R,, thirty-six 
miles west from Grafton. It is a valley 300 to 400 feet wide, 
filled with clay deposits, and separating Ten Mile creek, on 
the Monongahela side, from Middle Island creek, waters of the 
Ohio drainage. The summit of this coll, one mile west of Sa- 
lem, is 1,102 feet, A. T., while the bottom of the cut through 
it on the railroad or bed-rock under the clay-covered summit, 
is 1,081 feet, A. T. 
At the head of Rock Camp creek, another tributary of Ten 
Mile creek, which heads several miles (8 to 10 miles) north of 
Salem, there is another gap through the divide at exactly 1,143 
feet, A. T., as determined by an experimental R. R. survey. 
Also, Prof. T. M. Jackson informs me that there is a third gap 
through the same divide, one mile north from the one on the 
Baltimore & Ohio R. R., and through this the North West 
turnpike passes. 
The general elevation of the divide which separates the 
waters of Ten Mile and Middle Island creeks is 1,400 feet to 
1,500 feet, A. T. Here, then, are three gashes or wiers cut 
down 300 feet below the general level into valleys of consid- 
erable breadth from whose level summits the waters now go in 
opposite directions. 
The escape of the impounded water of lake Monongahela 
would sufficiently account for these old channels or colls. 
Curiously enough, there is another outlet at this same level 
(1,100 A. T.) near the head waters of the West Fork of the 
Monongahela, since the wide level summit at Arnold's, on the 
West Virginia and Pittsburgh R. R., is 1,095 feet, A. T., and 
the railroad is cut five to six feet below the level stretch of 
land which makes the divide between the Monongahela and 
Little Kenawha waters. This 1,100 foot divide at three or 
four different outlets from lake Monongahela, could hardly be 
a coincidence merely, but must represent the old colls tlirough 
which the surplus water of the imprisoned rivers escaped to 
lower levels during glacial times. 
