424 
GEOLOGY OF THE FOURTH DISTRICT. 
west or northwest wind brings few materials from that quarter. When the lake is higher 
than usual, even the low beaches are worn down, and the materials transported to other pans 
of the shore. 
The bank of the lake, from the Genesee river to the eastern boundary of the county, is 
from ten to thirty feet high. From ihc Genesee to the western line of the county, the shore 
is generally low, or raised into a beach a few feet above the lake. During the rising of the 
lake, which occurs at intervals, the beaches and sand-bars are removed, to be deposited in 
other places, and to fill up the mouths of streams. It therefore becomes a matter of import¬ 
ance to protect the shores from such effects, and from the loss of land thus sustained. To do 
this, trees and shrubs should be permitted to grow on the banks, and shrubs with strong 
roots might be planted to effect the same object. 
Boulders—Erratic Blocks* 
Boulders of different rocks are abundantly distributed over some parts of the county. They 
are most abundant north of ihe mountain ridge, and over the gypseous rocks in the south part 
of the county. In many places the surface is literally covered with them for a considerable 
extent, and again for a mile or two few are seen. These boulders are of the primitive rocks, 
as granite and gneiss, and of sandstone from the lower formation. Granite and sandstone are 
the prevailing boulders, but rounded and angular fragments of rocks of every formation, in the 
district, are found on the surface, some of them immediately above the original rock, and others 
at no great distance from it. The predominance of felspar is observed in all the granite 
boulders ; many of them being of that variety called Labrador felspar. This felspar is very 
indestructible, and masses of that rock form some of the largest boulders in the county. 
Some of the spherical masses are eight or ten feet in diameter. These are in many places 
so abundant as to be broken up and used for building materials. 
Soil. 
The prevailing soil of Monroe county is a gravelly loam; but we often find clayey loam, 
sand, etc. extending over considerable areas. Approaching the Genesee river on either side, 
the soil is more sandy ; this character prevails, also, along the Irondequoit. In some places 
the different soils blend into each other, and in others are quite distinct, or their limits are 
defined by the small streams. Sometimes changes of this kind are remarkable, where on 
crossing a stream the character of the soil is entirely different. The sandy soils are not defi¬ 
cient in carbonate of lime, and the sand from several feet below the surface is apparently as 
* We cannot, with propriety, restrict the term boulder to a rock distant from its original formation; for in the southern part of 
the State, rounded masses of the red sandstone arc boulders ; while masses of the same form are found on the limestone a few 
rods south, and in the soil above the original rock, which by that definition are not boulders. 
