No. 200.J 327 
LOCAL AND ECONOMICAL GEOLOGY. 
Monroe County. 
Surface of the Country^ Streams^ ^c. 
The general elevation of the northern part of this county is about 
three hundred or three hundred and fifty feet above Lake Ontario.— 
All that portion of the county south of the canal maintains about this 
elevation, if we except the diluvial hills, which rise to the height of 
from fifty to one hundred feet. On the north of the canal the surface 
declines gradually, and almost imperceptibly, to the lake shore; on the 
east side of the Genesee it is more uneven than on the west. In the 
northern part of the county, particularly north of the ridge road, the 
surface is remarkably even. We here find scarcely an undulation or 
depression disturbing the uniformity, except the channels of the present 
streams. 
East of the Genesee, particularly in the vicinity of the Irondequoit 
creek and bay, the country is very much broken into deep ravines and 
high ridges. These ridges or hills are composed chiefly of fine sand, or 
sandy loam, with strata of pebbles or boulders near the bottom. Most 
of the boulders in these hills are from the rocks in the vicinity, those of 
the primitive rocks being comparatively few in number. In this and 
some other respects the diluvium along the Irondequoit diflfers from that 
of any other part of the county. There have been vast accumulations 
of diluvial matter about the head of Irondequoit bay, and along its 
shores. It appears as if at one time this had been a great water course, 
and that some inundation of sand, gravel, &c. had filled it up and 
changed the direction of the stream. The sand of these- hills is stratifi- 
ed, and the strata often curved, or inclined at different angles. The 
banks of the bay are high, with deep ravines scooped out by the action 
of the smaller streams. 
The bed of the Irondequoit at Penfield, is much lower than the bed 
of the Genesee at Rochester and farther south. From examining the 
surface of the country this seems the most natural course for the Gene- 
see, and it may at one time have flowed in this channel. The Ironde- 
quoit is now a small stream, pursuing its course in a deep valley of de- 
nudation, showing that some more powerful agent was formerly active 
in this quarter. 
Farther south and distant from the streams, through the towns of 
Penfield, Perrinton, Mendon, &c. the diluvial hills are of moderate 
elevation, giving a gentle undulating appearance to the country. In 
