194 
GEOLOGY OF THE FOURTH DISTRICT. 
0 
York and Leicester, and the shore of Lake Erie at Eighteen-mile creek, as the most impor¬ 
tant and interesting points, and which will give all the desired information of this group in the 
Fourth District. 
Thickness. — The thickness of this group on the eastern limit of the district cannot be less 
than 1000 feet. There are a few undulations in the strata which may mislead in the esti¬ 
mation, to a small extent. Each of the members noticed thins gradually toward the west, 
until on Lake Erie it is less than half that amount. The whole thickness visible at this point 
is about one hundred feet. The Moscow shale, which in the eastern part of the district is 
fifty or sixty feet thick, is on Lake Erie 15 feet thick, and the lower members have diminish¬ 
ed in equal proportion; the shale of Ludlowville, known by the great numbers of Avicula, 
Cypricardia, &c. is scarcely a foot thick in the west. 
Mineral contents of the rock. — From the nature of the rock, and the absence of all distur¬ 
bances and intrusive rocks, it will be presumed that there are few simple minerals. Those 
which do occur are usually in the concretions ; crystallized carbonate of lime and baryta, and 
sometimes blende and galena occur in these bodies. Iron pyrites occurs in all situations, and 
from its decomposition result sulphate of alumina and sulphate of iron. 
The presence of blende, galena and other minerals proves that, under more favorable cir¬ 
cumstances, these rocks might have been somewhat metalliferous ; but being, in its present 
state, an unaltered mechanical deposit, the substances of this kind which it contains are dis¬ 
seminated through the mass, and the quantity is so minute as to be unappreciable while so 
diffused. 
Springs. — From the generally impervious nature of the rocks composing this group, it 
gives origin to numerous springs which rise to the surface in all situations. Wherever the soil 
is thin above the rock, the place is manifested by a wet or damp soil; and though there are 
few prominent and important springs, yet the water is carried to the surface, and oozes out 
over large spaces. Water is easily procured by digging wells in all situations where this rock 
underlies the surface, unless it be too deeply covered with alluvion. This is the condition in 
some parts of Bloomfield, Ontario county, where the rock has been deeply excavated, and 
the space afterwards filled with an immense deposit of northern drift, which rises into innume¬ 
rable hills and long ridges. From the great number of low conical hills clustered together in 
these situations, they are known by the name of the “ Hopper hills." 
Agricultural characters of the group. 
The soil resulting from the decomposition of these rocks, when unmixed with foreign ma¬ 
terials, varies from a tolerably pure marly clay to clayey loam ; but the prevalence of northern 
drift over a large part of the surface occupied by this group, has essentially modified the cha¬ 
racters of the soil covering it. The sandy calcareous portion of the shale has given origin to 
a clayey loam, which, in some places in the eastern part of the district, remains nearly un- 
