PYROCRYSTALLINE LIMESTONE. 
79 
words, the mass was erupted through cracks or fissures in the 
rock. 
It contains scapolite, hornblende and pyroxene, spinelle, 
octahedral iron, fer-olgiste, graphite, mica, talc, phosphate of 
lime, brown tourmalin, serpentine, &c. The districts of this 
variety of limestone are limited. In St. Lawrence and Jefferson 
counties it occurs just within the band of the lower Silurian 
rocks; in Essex and Clinton counties, at Moriah and near Clin- 
tonville; also in the western parts of Essex and eastern part 
of Hamilton counties, in the vicinity of the Adirondack iron 
works; in Canada West, also, twenty miles west of Ogdens- 
burg. This district is identical with that of St. Lawrence and 
Jefferson counties. The granite of the Thousand islands lies 
between the two districts, and is entirely destitute of limestone 
of this kind and the minerals it contains. In Orange county, 
New York, and the adjacent part of New Jersey, Sussex county, 
primary limestone, containing spinelles and most of those min¬ 
erals already noticed, forms a band of considerable extent. 
The red oxide of zinc, sapphire, and chondrodite are minerals 
which have not as yet occurred elsewhere, excepting the latter, 
which is found in small quantities only in northern New York. 
Fig. 9. 
a Potsdam and Calciferous Sandrock, 1 1 Hornblende, 2 2 Limestone, 3 3 
Gneiss, 
In structure this rock scarcely differs from granite. It is 
subject to disintegration, and suffers more from the action of 
atmospheric agents than granite. It has been maintained that 
