ONONDAGA SALT GROUP. 
125 
two ranges of plaster beds, occurs on Allen’s creek at Garbutt’s mills. The upper part 
of the section on page 119 is constructed from this locality. The lowest range of beds is 
best developed on the north side of the creek, where the rocks are covered with only a 
small depth of soil. The surface is raised into small rounded hillocks of a generally uniform 
height, and with depressions communicating over a considerable space, giving the appearance 
as of little mounds of earth. After removing the soil to a small depth, the rock appears, pre¬ 
senting the same convex or rounded contour as the surface above. The strata are usually 
thin, and present an appearance as if broken up by some elevating force from beneath. 
Below the rock lies a spherical mass of gypsum, upon every side of which the strata dip 
till they assume their original horizontal position. The proximity of these masses however 
is often so close that the strata continue undulating, being depressed between and elevated 
above the beds of gypsum. The woodcut below represents a section of two beds of gypsum 
at this place. 
49 . 
The elevation and breaking yp of the strata was doubtless caused in part by the expansion 
of the gypsum during solidification, (it being more or less crystalline,) while the strata above 
were partially indurated. In the lower beds, where the surrounding mass of rock is princi¬ 
pally a soft marl or shale, no such evidence is perceived, except perhaps in a slight degree. 
(See woodcut, page 123.) In this case the surrounding mass was probably in a yielding con¬ 
dition at the time of the solidification of the gypsum, and consequently the particles of the 
one gave place to the other, presenting no evidence of force. This is further proved by the 
continuation of a semi-crystalline siliceous stratum through a bed of gypsum, while the marls 
above and below, though doubtless originally equally continuous, have been displaced to give 
room to the gypsum, which with a stronger tendency to concentration, has accumulated into 
flattened spheroidal or low conical masses. Wherever the carbonate of lime was in such 
proportion as to induce a tendency to crystallization, the strata appear to have become in 
some degree consolidated before the gypsum ; on the other hand, where the proportion of 
argillaceous greatly predominated over the calcareous matter, the tendency to crystallization 
was lessened or entirely prevented, and the gypsum consolidated before the surrounding mass. 
The same operations appear to have gone on here, as we often perceive in artificial com¬ 
pounds, where the tendency to crystallization is much stronger in one body than in another. 
These beds of gypsum are usually from four to eight feet below the surface; few being 
worked at the latter depth, the expense being too great. There is sometimes an appearance 
of a third range of beds, but this is not continuous. The rock above is so much broken as 
freely to admit the surface water, and thus broad fissures are often worn in the softer marls; 
and sometimes even in the mass of gypsum. 
