No. 276.] 
305 
piece of solid marl, having its faces and edges grooved or striated as in 
the pseudomorphic crystals of muriate of soda.* The gray marl is also 
traversed by seams of gypsum, generally flesh coloured or reddish, in 
such quantities that the whole is ground and sold for plaster. Both 
the green and gray marl rapidly disintegrate and form a tough clayey 
soil. 
The second series is developed near Port Gibson, and also about a 
mile distant, at an elevation of twenty-five or thirty feet above the Erie 
canal. An argillaceous limestone appears on or near the surface in 
low knolls or hillocks; this rock, on removal, is found to be fractured, 
as if upraised from beneath, and at the depth of four or six feet, is found a 
flattened, spheroidal mass of gypsum. It is always of this form, and quite 
disconnected with the surrounding rock« This gypsum is fine grained, 
compact, contains no Selenite, and in general appearance is quite diffe- 
rent from that last described. The surrounding fractured rock is in thin 
layers from four to six inches thick, which break into pieces from one 
to three feet square. The surfaces present numerous little seams or 
cracks, similar to those produced in clay on drying, and the sides of 
these are all smooth, and appear worn as if by the passage of water. 
This character is very constant, so far as has been observed, and serves 
better than any other to distinguish the rock. The external colour, af- 
ter weathering, is that of common clay; on fresh fracture, it is bluish, 
often nearly black. Water is with difficulty obtained along the extent 
of this formation ; the fractured rock beneath admitting the percolation 
of water so rapidly as entirely to drain the soil, the little hillocks be- 
come in summer too dry to support vegetation. Very little gypsum 
has been obtained from this series in Ontario county, though it seems 
to be the same which furnishes a great part of that mineral in Monroe 
county. It will doubtless be explored after the supply along the Ca- 
nandaigua outlet in Phelps, becomes exhausted. 
The third series embraces the gypsum which is extensively quarried 
in the town of Phelps, between Vienna and the town line of Manches- 
ter, along the Canandaigua outlet. West of this point, one or two 
masses are seen in the bank of the outlet; and with this exception, and 
a single bed recently opened near Victor, the town of Phelps furnishes 
all the gypsum from the county. This with its associated rocks are 
very similar in character to those on the Seneca outlet. It occurs in the 
same irregularly shaped or somewhat conical masses, producing no dis- 
turbance in the surrounding strata; while the lines of stratification in 
* Their form, however, is less regular, and they occur much lower in the series, 
[Assera. No, 275 ] 39 
