GEOLOGICAL SOCIETY OF LONDON. 
131 
below tlie Whirlpool, must have been 300 feet higher than the 
present bed, so as to form a barrier to that body of fresh-water, 
in which the various beds of fluviatile sand and gravel above- 
mentioned were accumulated. This barrier was removed when 
the cataract cut its way back to a point further south. The au- 
thor also remarks that the manner in which the fresh-water beds 
of the Whirlpool and Goat Island come into immediate contact 
with the subjacent Silurian limestone, shows that the original 
valley of the Niagara was shaped out of limestone as well as 
drift ; hence he concludes, that the rocks in the rapids, above 
the falls, had suffered great denudation while yet the falls were 
at or below the Whirlpool. Mr. Lyell thinks that the form of 
the ledge of rock at the Devils Hole, and of the precipice 
which there projects down the river, proves the falls to have 
been once at that point. An ancient gorge, filled with stratified 
drift, which breaks the continuity of the limestone on the left 
bank of the Niagara, at the Whirlpool, was found to be con- 
nected with the Valley of St. David^s, about three miles to the 
north-west ; this ancient valley appears to have been about two 
miles broad at one extremity, where it reaches the great escarp- 
ment of St. David^s, and between 200 and 300 yards wide at the 
other end, or at the Whirlpool j its steep sides did not consist 
of single precipices, as in the Ravine of Niagara, but of succes- 
sive cliffs and ledges. After its denudation, the valley appears 
to have been submerged and filled up with sand, gravel and 
boulder clay, 300 feet thick. The author passes to the general 
consideration of the boulder formation on the borders of Lakes 
Erie and Ontario; and in the Valley of St. Lawrence, as far 
down as Quebec. Marine shells were observed in this drift in 
several localities — at Montreal, attaining a height, probably, ex- 
ceeding 500 feet above the level of the sea. Similar shells were 
found as far south as the western and eastern shores of Lake 
Champlain ; they are all northern species, and imply a former 
colder climate. Rocks, in contact with the drift, are smoothed 
