PYROCRYSTALLINE LIMESTONE. 
81 
also; but when in its most characteristic condition, it is more 
like a furnace slag than a crystal. Many pieces look as if 
while softened they had been drawn out or extended. Some¬ 
times, again, the quartz has assumed a globular form, or 
the shape of a slag or of a bead. Notwithstanding, however, 
the similarity of the masses of quartz to furnace slag, it may 
not prove that those forms and conditions are due to heat; for 
globular quartz has been found in the calciferous sandrock, in 
which case it can not be referred to heat as a cause. Still, in 
the case of primary limestone, the circumstances are such as to 
favor the views I have expressed, and that the appearance of 
the masses referred to may be regarded as evidences of the fact. 
Crystals imbedded in this rock often contain large particles 
of limestone in their interior. Pyroxene, quartz, phosphate of 
lime, and brown tourmalin are rarely free from this substance. 
The cavities containing the limestone are never angular, but 
always rounded. The imperfections of the crystals are due 
mainly to this cause. All the large crystals especially are sub¬ 
ject to these faults, even the zircons, spinel]cs, and corundums 
are liable to them. I have noticed three districts in northern 
New York where this rock forms the most striking feature in 
the geology of each: 1. That of Jefferson and St. Lawrence 
counties, which has been already referred to; 2. Essex county, 
near lake Champlain, which may be traced, with very slight 
interruptions, into Warren county, forming a belt which runs 
northeast and southwest; and 3. Orange county. This last 
district extends into Sussex county, New Jersey, and forms a 
remarkable series of minor belts, which are prolonged to the 
southwest. In these three districts the limestone is very coarse 
and crystalline. Its true structure is like that of granite, and 
the lamination is generally obscure. Another and independent 
belt belongs to the Hoosick Mountain range. The beds crop 
out at intervals from Canada to Long Island sound. Their 
form is oblong, and the structure of the masses crystalline. 
They are in gneiss, and very frequently in close relation with 
hornblende. These beds are laminated, partaking of the structure 
