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; 

 iior 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. 



* X4ieut. Mather's Geology. 



