384 
GEOLOGY OF THE FOURTH DISTRICT. 
The great difference in elevation between Lake Ontario and Lake Erie, and the occurrence 
of the Cataract of Niagara, form one of the most striking features in the topography of Wes¬ 
tern New-York. The difference in elevation of the upper great lakes is comparatively small; 
they being nearly in the range of the strike of the strata, while the passage from Lake Erie to 
Lake Ontario is directly across the line of dip* Lake Erie is three hundred and thirty-four 
feet above Lake Ontario, and the greater part of the descent from one to the other is overcome 
by the rapids and falls of the Niagara river in the space of one mile. 
The series of limestones forming the Helderberg mountains in the eastern part of New- 
York, extend westward throughout the whole length of the State, gradually diminishing from 
the thinning out of some of the members ; and crossing the Niagara at the outlet of Lake 
Erie, they extend far westward into Canada, and form, for many miles, the southern shore of 
Lake Huron, and the eastern shore of Lake Michigan. This limestone dips to the south, 
passing beneath the water, and forming to some extent the bed of Lake Erie. It forms the 
second great terrace south of Lake Ontario, over the outcropping edge of which, on the north, 
we descend to a low, level country, underlaid by the shales and marls of the Onondaga salt 
group, which extends for fifteen or eighteen miles. Beyond this point there is a gradual and 
almost imperceptible ascent for seven or eight miles, when we come to the edge of the first 
great terrace overlooking the present valley of Lake Ontario. From this we plunge down for 
two hundred and fifty feet, over the outcropping edges of various strata, which here terminate 
abruptly, to the low table land bordering the lake. From the base of this escarpment, the 
plateau, on which Lewiston and Queenston stand, slopes almost imperceptibly to the level of 
the lake, which is seven miles distant, and one hundred and twenty feet lower. 
A great portion of the country for twenty miles north of the southern terrace is so low and 
level, that a rise in the river for thirty feet would inundate an extent of many miles on both 
sides.t The ascent from this low country toward the north is very gradual; but when we 
arrive at the edge of the great terrace above Lewiston, the elevation is thirty-eight feet above 
Lake Erie. The accompanying section from Lake Erie to Ontario, presents an outline of 
this portion of the country. 
This great terrace and escarpment, through which the Niagara makes its way into the valley 
of Lake Ontario, is known in New-York as the Mountain Ridge, and in Canada as Queenston 
Heights. It continues to the westward of Niagara river, curving around the head of Lake 
Ontario, and thence trending westerly, some of its members extend beyond the Mississippi 
river. To the eastward, it is distinctly traceable as far as the Genesee river; beyond which, 
it merges in the general level, and the rocks forming it disappear almost entirely, from thinning 
out, before reaching the Hudson river. The abrupt termination of these various strata upon 
the face of the escarpment, prove conclusively the extent and effect of denuding agency upon 
* The geological positions of Lake Superior and Lake Ontario, the highest and the lowest of this chain of lakes, correspond 
very nearly with each other. 
f By means of the dam at Black-Rock, the water is taken from Lake Erie into the Erie canal, and carried through the Tona- 
wanda creek, descending the terrace at Lockport by a cutting of less than thirty feet. 
