CRYSTALLINE LIMESTONE. 79 
blende schist. It would appear that the fusion of 
clay slate, whether primary or secondary, is, under 
various circumstances, capable of generating either 
the common trap rocks or the hornblende slates ; 
nor is it, perhaps, difficult to explain, by a more 
gradual cooling, and, consequently, a slower crys- 
tallization, the particular causes which may have 
determined the latter rather than the former effect." 
2. Crystalline Limestone, 
Crystalline limestone is a common rock, of which 
statuary marble is a variety. It forms extensive 
beds in several of the primary rocks, especially mi- 
ca slate, with which it is often intermixed. It oc- 
curs more rarely in granite than in gneiss, and when 
it is met with it is coarser grained than when found 
in mica slate or common slate. Crystalline lime- 
stone is granular, contains no organic remains, is 
imperfectly translucent, and usually of a white col- 
our, though sometimes clouded with black, yellow, 
or red. A bed of this rock extends, with few in- 
terruptions, 700 miles in length, beginning in Cana- 
da, passing through Vermont, the western part of 
Massachusetts and Connecticut, thence through 
New-York, New- Jersey, &c., to Virginia, and is 
extensively quarried in a great many places, and 
supplies most of the marbles used in this country.* 
3. Quartz Rock. 
Quartz rock is an aggregate of grains of quartz, 
which are either in minute crystals, or, in many 
cases, slightly rounded, occurring in regular strata, 
associated with gneiss, mica slate, &c., into which 
it often passes by an imperceptible gradation. 
Quartz rock sometimes forms high mountains, as 
Monument Mountain in Stockbridge, Mass., which 
is more than 1000 feet high ; also some of the ranges 
of the Rocky Mountains. 
* Lieut. Mather's Geology. 
