142 The American Geologist. March, 1998 
Hy 
i 
| 
Clinton 
Sh. 
Ai aygara as. 
Seo J See IL 
SECTIONS IN THE NIAGARA GORGE. 
to the farthest line of erosion fourteen feet above the foot; that 
is, the extreme erosion here was fourteen feet in fifty-five 
years. The average of fifteen measurements in the Clinton 
shale between 800 and 1,100 feet, at twenty-foot intervals, was 
13.6 feet for the extreme amount of erosion in fifty-five years, 
being three inches per year. 
Section II. was made 6,317 feet from the tunnel, in the 
Niagara shale. The foot of the cut was thirteen feet from the 
outer rail, and the greatest lateral extent of erosion, thirty- 
three feet, making the amount twenty feet in fifty-five years. 
The average amount of greatest erosion along this exposure, 
as shown by eleven measurements between 6,140 and 7,325 
feet from the tunnel, was 14.8 feet, or three and one-quarter 
inches per year. 
From this it appears that the rate at which the Clinton and 
the Niagara shale crumble away where unprotected is one and 
a half inches per year, that being the actual rate at which it 
has crumbled along the faces where measurements were made. 
