found in the Potsdam Formation. 19 
haps not more than fifty feet. We have thus a bench-mark to 
test the rise not only of these strata at Beauharnois, but of their 
equivalents, wherever else they may be met with. 
Finding that this ancient sand bank was exposed at the ebb 
of tide we naturally look out for some coast to which it was 
_ related. The Potsdam sandstone terminates some twenty miles 
REESE “ip Ss 
Se FS SO 
One-thirtieth natural size. 
to the north at a very low angle against the foot of the Lat 
ide hills, which rapidly rise up 500 or 600 feet above the Silu-. 
rian plain. There is little doubt that we have in the flank of 
Boas Si —_- a _palergpeg 
_ ,0f«which is thus traceable from Labrador by the northwest, to 
the Areti distance of 8,000 miles. But though w 
those hills the ancient limit of the Lower Sil 
Mribicenigs * 
iy 
