48 
GEOLOGY OF THE FOURTH DISTRICT. 
From many circumstances, it would appear that the lower part at least of this deposit was 
thrown down rapidly. The quantity and uniform nature of the mass show but one source 
for the material for a considerable period of time, there being no alternation or intermixture of 
different substances. If we consider the condition of the water rendered turbid by such a 
quantity of mud, and highly colored by the iron, it is not surprising if organic forms did not 
exist. 
In the grey sandstone (second division), animal organic remains are abundant in some places, 
though the forms are not numerous. At Medina, in the upper part of this mass, shells of 
Lingula, Pleurotomaria and Cytherina occur in great profusion. These likewise occur at 
other places, but less abundantly. At that place, in the bed of the stream above the falls, the 
Pleurotomaria are crowded together in such numbers as to constitute almost entirely a distinct 
stratum several inches thick. The Lingulae and Cytherinas are scarcely less abundant, forming 
the greater part of the stratum. In other places these all disappear, except the Lingula, which 
preserves its place much longer than the others. Some portions of the rock where these fos¬ 
sils occur is tinged with red, and on decomposing becomes brown, but never of the deep color 
of the mass above or below. 
The following are the more common forms found in this rock, at Medina and Lockport: 
c. 
1 & 2. Pleurotomaria pervetusta, (a cast.) 
3. Cypricardia alata. 
4. Orbicula parmulata. 
5. Lingula cuneata. 
C & 7. Bellerophon trilobatus, (a cast.) 
8 & 9. Cypricardia orlhonota, (a cast.) 
Besides the fossils figured, the Cytherina is abundant; there is also a small shell resembling 
the Nucula? laevis of Murchison, and an undescribed Avicula, with one or two other shells, 
and, rarely, fragments of Orthoceroe. Those figured in the woodcut, with the exception of the 
Orbicula, are associated at Medina, and we find the same at Lockport. The individuals like 
Nos. 3 and 8 are more abundant at Lockport than elsewhere. 
In the upper division, the only fossil known is the Dictuolites Beckii of Conrad (Plate I. 
fig. 1). This is one of the most interesting fossils found in the rock, often covering large 
surfaces with its strong rigid branches and beautiful interlaced rootlets. A remarkable pecu¬ 
liarity of this fossil is the angular or reticulated structure presented by the branches, so unlike 
