260 
[Assembly 
gregate." Within the layer of 8 inches, are two others more compact, 
of about an inch thick. These have been broken in many places, so 
that the parts no longer hold their original parallels, the enveloping part 
showing but few signs of disturbance. 
In the material which covers the gypsum of the upper range, the arch- 
ing is but perceptible, owing to its soft nature, whilst in the lower range 
the arching is common, and formed of harder, fine grained and a com- 
pact material. A considerable portion of all the arches resemi)le in 
fracture the material of which the porous rock is composed. These 
facts show that a hardening or consolidation of the matter of the arch- 
ing took place before the gypsum wholly separated from the mass in 
which it must have been diffused, or, in other words, before it acquired 
the form in which we find it. On the contrary, where the arching does 
not exist, the particles which compose it, when pressed upon by the 
forming plaster, would have retired to the place of the least resistance, 
as is instanced in the material which encloses the two thin layers in the 
eight inch bed of the water lime of Chittenango. 
There are two localities in which the porous rock is found in greater 
thickness than elsewhere met with, and merit examination from the con- 
nection with the immediate salt region. 
The one is on the road from Amboy and Bellisle to the turnpike, a 
few miles west of Syracuse, immediately back of the tavern, and in the 
rise to the top of the hill. The other is on the Footsheet road, ascend- 
ing from Syracuse to Mr. Jeptha Colvins. 
At the first locality, towards the bottom of the hill, there are about 
twenty feet of these dark porous layers, and of configurations frequently 
met with elsewhere, probably belonging wholly to common salt or else 
to sulphate of lime, not having yet determined. To these others suc- 
ceed, and then those with vertical fissures, with a few small thin shelled 
bivalves, similar to those of Bull's quarry, also a few small fucoides. The 
terminal mass is the " vermicular rock," from four to five feet thick. 
The locality near Syracuse is of greater interest, for besides the two 
porous masses of the hill to the west, there exist at no great distance 
below the upper porous rock, a series of highly crystalline aggregates, 
wholly different from every product yet met with in the Third District, 
if we except the dykes noticed in the last report, and a few thin ones 
yet to be mentioned, which are found near Ludlowville, above half a 
mile east of the village. The description of these crystalline rocks, 
