120 
GEOLOGY OF THE FOURTH DISTRICT. 
visible within a short distance on the north side of Black creek. In an excavation half a 
mile east of Churchville, some loose masses of the Niagara limestone were found, but no 
rock of this group. 
In the northern towns of Genesee county, the lower portion of this group were seen in se¬ 
veral places, mostly however as excavated from wells. The depression along the line of the 
Tonnewanta creek, which is near the northern margin of this formation, prevents any expo¬ 
sure of the rock. Along the whole distance to the Niagara river, the surface is deeply co¬ 
vered by drift, and it is only in a few points or from artificial excavations that the mass 
becomes visible. 
2. The prevailing features of the second division of this group are a green and ashen marl, 
with seams of fibrous gypsum, and red or transparent selenite, and often embracing nodules 
of compact gypsum. This occurs in the vicinity of Lyons, and at numerous points farther 
west. It crops out on the road some distance northeast of Newark, and at Lockville it has 
been excavated from the bed of the canal for the construction of the enlarged locks. Here it 
contains seams and small irregular masses of reddish lamellar gypsum. Its general charac¬ 
ter at this place is a greenish grey compact argillaceous marl, which crumbles rapidly on 
exposure, and forms a tenaceous greenish clay. Near Newark the mass is variegated with 
red, and red spotted with green, and some portions are of a light ashen color. It is marked 
by the presence of reddish and transparent lamellar gypsum, and seams of fibrous gypsum. 
The same occurs farther west, and is seen in the banks of the canal near Palmyra. 
Thence to the Genesee river it is scarcely seen upon the surface, but has been found in 
digging wells. 
Westward, we find the same rock in Bergen, Byron, Elba and Alabama, in Genesee 
county. About one mile north of Bergen Centre the greenish gypseous marls are excavated 
along the line of the railroad. In digging wells in the same neighborhood, these marls with 
fibrous gypsum and selenite are usually encountered, and it generally requires that they be 
penetrated to a considerable depth before a permanent supply of water can be obtained. This 
character is the prevailing one through the counties of Monroe and Genesee. 
There are few points where a natural exposure of these rocks can be obtained, and it is 
principally from artificial excavations that we have any knowledge of their character. 
Throughout its whole extent in Erie county, there is scarcely a natural exposure of the 
rock, and the depth of the drift is so great that it is only in a few points that excavations 
have been made to any considerable depth below it. 
3. The third deposit embraces all the gypsum beds of the district which are of economi¬ 
cal importance. Although this mineral occurs in the deposit below this, as before stated, in 
seams and small nodules, yet it has never been discovered in quantities of any importance, 
and there is no probability that much will be found. The greater part of this division con¬ 
sists of grey or ash-colored marls and shales, with thin bedded shaly limestones, which are 
usually of the same color, though sometimes much darker. 
