454 - 
geology OF THE FOURTH DISTRICT. 
piece of solid marl, having its faces and edges grooved or striated as in the pseudomorphic 
crystals of common salt. The grey marl is also traversed by seams of gypsum, generally 
flesh-colored or reddish, in such quantities that the whole is ground and sold for plaster. Both 
the green and grey 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 ele¬ 
vation 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 frac¬ 
tured, as if upraised from beneath, and at the depth of four or six feet, is found a flattened, 
spheroidal mass of gypsum, quite disconnected with the surrounding rock. This gypsum is 
fine-grained, compact, contains no selenite, and in general appearance is quite different 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 color, after 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 become 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 finishes a great part of that mineral in Monroe county. Jt 
will doubtless be explored, after the supply along the Canandaigua 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 Manchester, 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, pro¬ 
ducing no disturbance in the surrounding strata, while the lines of stratification in the marl 
pass through the beds of gypsum, and in several instances where one or two thin courses of 
hard argillaceous limestone occur in the former, these also are continued through the latter, 
the intervention of the rock merely breaking the continuity of the plaster, without otherwise 
affecting it. In this series, the force of aggregation or chemical attraction seems not to have 
been sufficiently powerful to separate the gypsum from all surrounding materials, consequent¬ 
ly we find it much intermixed with the marl; and wherever the attraction of particles was 
stronger than in either of these, as in the limestone, the strata continued their course through 
the mass, scarcely interrupted at all. The greater tenacity of the latter may have prevented 
the mobility necessary to an entire separation of particles, and from this cause in part may 
arise the admixture of substances. 
