ONONDAGA SALT GROUP. 
121 
Owing to the deep denudation in the direction of Seneca and Cayuga lakes northward, the 
whole group has been removed to so great a depth as to offer no evidence of its existence. 
Along the line of the Erie canal, the middle division appears a short distance before reaching 
Clyde. The third division, with the higher range of plaster beds, appears at Seneca falls, 
and along the outlet of the lake for three miles eastward. Extensive beds of gypsum are here 
exposed in both banks of the gorge, the largest on the north side. The surrounding mass is 
a light ashen friable marl, with a few thin strata of impure limestone towards the top. Where 
exposed alone, it has the character of a loamy clay, containing some carbonate of lime ; and 
in the vicinity of the masses of gypsum, contains some of that mineral disseminated through 
it. The enclosed masses of gypsum are somewhat conical, though often irregular from the 
encroachment of the enclosing rock. The marl and gypsum are both stratified, the lines of 
division in the former often extending through the latter. There is usually a considerable 
admixture of earthy matter in the gypsum, and it appears as if segregated from the mass 
during its consolidation, by a well known law of attraction among particles of the same kind. 
The following woodcut is an illustration of the largest mass seen along the outlet below 
Seneca Falls village, and gives the usual appearance of the beds of the upper division, as 
exhibited in the Fourth District: 
45. 
1. Compact granular gypsum, with lines of stratification. 
2. Soft decomposing gypseous marl. 
3. A lateral extension of the bed, with a greater admixture of argillaceous matter. 
Along the outlet of Canandaigua lake, in the town of Phelps, we find a good exposure of 
the higher range of plaster beds. The general appearance, and the character of the succeed¬ 
ing masses, are like the same at Seneca Falls. The marls are mostly ash colored, with a 
few strata of more siliceous character which are bluish. The only beds explored are those 
[Geol. 4th Dist.] 16 
