8 Captain Bayfield on the 
ing fact. Any diminution which may be, must be almost 
imperceptibly gradual, and it would require constant, ac- 
curate, and regulatly recorded observations during a great 
number of years, to render the fact indisputable. The streams 
which discharge into Lake Superior amount to several hun- 
dred in number, aud the quantity of water supplied by them, 
is many times greater than that discharged at the Falls of 
St. Mary, the only outlet. There is however no reason to 
imagine, from this circumstance, that the quantity of water 
increases, for it is absolutely necessary that there should be 
a supply very far exceeding the discharge, to replace the im- 
mense expenditure arising from the evaporation from so 
extensive a surface. 
8. The surface of Lake Superior is about 623 feet above 
the tide water ofthe Atlantic Ocean. Of this height, 565 
feet, the elevation of Lake Erie, has been ascertained by 
the United States’ Engineers, when leveling for the Great 
Western Canal of New York, 22 4 feet have been also mea- 
sured as the amount of the Fall of St. Mary's Rapids. Of 
the rest, which is merely estimation, 30 feet have been allow= 
ed as the difference of level between Lakes Erie and Huron; 
and we think that 10 feet are not too much for the whole 
descent of the River St. Mary’s, exclusive of the Falls. 
Having now mentioned these preliminary matters, which 
although not strictly geological, are in some measure con- 
nected with that subject, and are besides intrinsically inter- 
esting, we proceed to take a rapid and general view of the 
various rock formations. 
9. Lake Superior is situated by the southern side of 
that great chain of Hills composed principally of rocks of 
the inferior or submedial orders,* which to the eastward, 
forms 
* it will be perceived that we adopt the arrangement of the 
Revd. W. D. Conybeare in his Introduction to the Geology of 
England and Wales, 
