No. 200. J 
305 
mation of gypsum, by a decomposition of the limestone, but there is 
very little pyrites now remaining in the rock. The masses of gypsum 
are sometimes stained on their edges with iron, and bog ore is of fre- 
quent occurrence in the neighborhood. Hydro-sulphuretted springs are 
common, and the water of some wells is of similar character. The wa- 
ter of some of these springs corrodes iron rapidly. In the town of 
Eyron, Genesee county, there is a spring arising from this formation, 
containing free sulphuric acid. 
Immediately surrounding each mass of gypsum we find layers of 
loamy clay, called ashes by the workmen. This ashes contains disse- 
minated particles, and sometimes scarcely aggregated, friable masses of 
gypsum. We have in this "ashes" precisely what would remain of 
the argillaceous limestone, should we abstract the calcareous matter by 
sulphuric acid, or any other process. 
It is said by the inhabitants, that the small elevations indicating the 
presence of gypsum are not observed till after the country has been 
cleared of its forests, or in places where there has never been trees grow- 
ing. These changes in the contour of the surface are observable from 
one year to another. In some places a mass of gypsum has formed un- 
der a building, altering the level of its foundation and disturbing its equi- 
librium. Points on the surface which are now but slight elevations, 
will in a few years become more elevated. However unaccountable 
these circumstances may appear, I have no reason to discredit the asser- 
tions of numerous respectable authorities. 
In some places, where the rocks of this formation approach the sur- 
face, they are decomposed into a clayey marl, much resembling the or- 
dinary clays, and it has sometimes been used for similar purposes. This 
marl, however, contains too much carbonate of lime for the common 
purposes of clay. In some places, where this rock is calcareous, the 
surface is cracked or furrowed in every direction, like a bed of wet clay 
drying in the sun. These furrows are water- worn, and give a singular 
appearance to the rock. 
The gypsum beds are commonly from four to eight feet below the sur- 
face; sometimes two tiers of beds are found, one overlaying the other. 
The crevices and fissures in the rock above the gypsum admit large quan- 
tities of water, and we often find a water-worn cavity or fissure in the 
bed of gypsum, and the channel through which the water escaped below. 
By this means any iron from decomposing pyrites might be carried off. 
[Assem. No. 200.] 35 
