GRANITE. This is one of the most abun dant rocks seen at or near the surface of the earth. It underlies the stratified rocks, and appears at some remote geological mra to have been in a fluid state from the effect of intense heat.
Granite is one of the most beautiful of rocks, and viewed mineralogically its composition is remarkable. Mica, felspar, and quartz, in distinct crystals, or else filling interstices be tween crystals, constitute the typical varieties ; but other minerals, such as hornblende, acti nolite, chlorite, talc, compact felspar, steatite, garnet, zircon, &a., enter into and sometimes considerably modify the aspect of granite, especially in colour, which varies much. Ex cept in a few cases, granite, as its name im plies, shows the grains of its component parts; the size of these varies extremely. Granite is indeed rather a name for a mode of aggrega tion than for a definite chemical or even mine ralogical structure ; and the varieties are thus too numerous to be distinctly named.
Granite is largely employed in building, especially in the more important engineering works. New London Bridge affords a beauti
ful instance of its use. It is also much em ployed in paving the London streets. When polished it presents a fine appearance; but the polishing is a work of great labour, on ac count of the hardness of the stone. Aber deenshire, Devon, and Cornwall, furnish our chief supplies of granite.
A very large block of granite, upwards of 20 feet long, and of the finest quality and colour, has lately been raised by the Cheesewring Granite Company, at their quarries, on tho Cheesewring-hill, near Liskeard, which is in tended to be sent to the Great Exhibition of 1851. The mass of stone, of which this formed a portion of the quarry, contained by measure ment the extraordinary quantity of above 4,000 cubic feet, or about 300 tons in weight.
A fine specimen of Irish 'granite is also to he exhibited, obtained from the Ballyholland quarries near Newry.