440 
GEOLOGY OF THE FOURTH DISTRICT 
NIAGARA COUNTY, 
We find the same rocks in this county as in the preceding ones. The Medina sandstone 
forms a broad band on the northern side of the county, reaching nearly to the line of the Erie 
canal, and the Onondaga salt group forms a narrow band on its southern edge. The Niagara 
and Clinton groups form a high terrace, extending entirely across the county, and are only 
interrupted at the Niagara river, pursuing their way beyond into Canada. This remarkable 
terrace furnishes a good opportunity of examining the rocks of these groups, and no locality 
offers so good facilities for this purpose as Lockport and the gorge of the Niagara. 
Surface of the country — Streams, $-c. 
The Mountain ridge* is the most remarkable feature in the surface of this county. This 
ridge gradually rises to the westward, and at the Niagara river is about three hundred and 
fifty feet above the level of Lake Ontario, and two hundred and fifty feet above the country 
on the north. At Lewiston, the whole descent to the north is made at one offset; but farther 
east it descends by two, making two grand steps, or terraces. This double offset is produced 
by the unequal hardness of the rocks ; a stratum of sandstone causing the lower one, while 
most of the rocks below and above it to the limestone are soft. In the eastern part of the 
county, this stratum of sandstone has so far declined that it dips beneath the general level of 
the country on the north. The mountain ridge passes through the towns of Lewiston, Cambria, 
' The terms “ mountain ridge ” and “ terrace” have been used indiscriminately ; the former is the name commonly applied, though 
the latter is more appropriate. 
