126 
GEOLOGY OF THE FOURTH DISTRICT. 
The dome-shaped elevations are said by the inhabitants not to appear till after the settlement 
and clearing of the country, and it is a general opinion that the gypsum continues to form at 
the present time. It is even asserted that stone walls have been overturned, and the founda¬ 
tions of buildings elevated by this process. Since the rocks must have become consolidated, 
and the gypsum formed, long anterior to the settlement of the country, as is evident from 
its appearance in the banks of streams, which excavated their channels long before the present 
vegetation flourished, these apparent phenomena must meet some other explanation. In the 
natural state of the country, the great accumulation of vegetable matter would prevent the 
prominent appearance of these little mounds, even if they existed. Since, however, we know 
that the surface water is rapidly drained off in these depressions, readily finding its way be¬ 
tween the strata and through the fissures, it carries with it a small quantity of the soil, which 
is repeated at every successive rain. As a natural consequence, the original inequalities of 
the surface of the strata are gradually developed, and in some places the more elevated parts 
become denuded of the soil which covered them. 
Beyond this point, there is a considerable space in the western part of Monroe county, 
where no beds of gypsum are known. 
In the north part of the towns of Leroy and Stafford in Genesee county, the lower range 
of beds appear, and are extensively worked at a few places. There is no evidence of the 
higher range of beds through these towns, or at any point farther west, and it seems probable 
that they have discontinued. In this county, the second range appear to be as well developed 
as elsewhere in the district. These beds are overlaid by the porous rock, which is so strongly 
marked in the Third District; here, however, the pores are rarely larger than a pin’s head, and 
usually compressed. This character is well developed at several beds, though not so obvious 
in all. The quality of the gypsum varies very much, the most easterly beds being very im¬ 
pure, and if not protected from the weather, will soon crumble down. Farther west the 
gypsum is more pure, and in some of the beds entirely free of foreign admixture, furnishing 
a good material for hard-finished walls. The same appearance of the surface is presented 
as in Monroe county, and it is sought for as an indication of the existence of the gypsum. 
The masses are all more or less spherical, and the strata above are elevated and broken as 
before described. 
Throughout the whole width of Erie county, this formation is covered to so great a depth 
with drift or alluvion, that there are only one or two places known where the rocks of the 
lower divisions are seen. The principal point is on the farm of Mr. Martin, in the north part 
of the town of Clarence. The rock is that portion coming between the two ranges of plaster 
beds; it consists of several thin strata of limestone, with cavities of the size of flax seeds, 
several often communicating, forming linear ones. A few incipient hopper-shaped cavities 
were observed, but their forms were quite indistinct. Some portion of the rock here exposed 
exhibits a tendency to a concretionary or contorted structure, presenting abrupt curvatures of 
the laminae, which could only have resulted after deposition. The surface of the strata 
presents the appearance before referred to, as if hacked with an axe, being the result of a 
weathering of the joints upon the surface. 
