100 
GEOLOGY OF THE FOURTH DISTRICT. 
little influence. In many places, however, for a small extent, the surface is clayey, and even 
extremely so, as if the materials of the lower rock had been deposited upon the higher. An 
example of this kind occurs a little west of the village of Lockport, where the limestone is 
covered by a clayey soil, while, a mile or two further east, the soil is a light loam. The 
latter character also prevails in some places near Rochester, and at other points along the out¬ 
crop of this limestone. This character of the soil, together with the rapid drainage to which 
it is subjected, from the fissures or joints in the limestone, as well as the proximity of the rock 
to the surface, has given rise to a different growth of timber, which everywhere marks the 
limestone terrace. While the country on the north and south sustains a forest of maple, 
beech, elm, ash, and the associated forest trees ; that along this limestone is indicated by oak, 
chesnut, and others of the same nature. 
Following the slope of the limestone southward, the soil becomes more clayey, and the 
surface more level. 
Organic Remains of the Niagara Group. 
One of the most striking features of this group, and particularly of the shale, is its vast 
number of organic remains. Shells and trilobites are the most abundant forms, though several 
species of Crinoidea are common. Corals of different genera and species are the predomi¬ 
nating forms in the limestone, while shells and trilobites are rare. In this group in the Third 
District, organic forms are rare, few species only being known ; while they become more 
abundant in Wayne county, constantly increasing in a westerly direction as far as Lockport. 
Along the Niagara river the means of examination are limited, notwithstanding the fine natural 
section; but in all accessible localities, the same fossils are found as elsewhere. 
We have, in the shale of this group, no less than six species of Trilobites and nine species 
of Crinoidea, with as many shells, which occur in no other group within the district, and have 
not been seen in any other rock elsewhere in the State. 
The partial or entire decomposition of the corals in the limestone has, in a great measure, 
prevented their affording the characteristic distinctions they otherwise might have done. 
TRILOBITES. 
Among the Trilobites, the following are known as characterizing the shale at Rochester, 
Lockport and other places. Two other species are known in this group, which will be found 
figured in a lithographic plate at the end of the volume, and there is still a third form which 
has not been described. 
