410 REPORT ON NATIONAL MUSEUM, 1886. 



with the microscope, though they are indistinguishable to the naked 

 eye. Those granites which contain hornblende also frequently contain 

 mica, but it is noticeable under such circumstances that the mica is 

 always the dark variety, and an example of a granite which contains 

 both hornblende and muscovite is unknown.* Although epidote is a very 

 common constituent of our granites in the form of microscopic crystals, 

 the cases in which it occurs as chief accessory are quite rare. So far as 

 observed it is always of a green color, and wheu present in any quan- 

 tity is readily noticeable on this account alone. The pink granite of 

 Dedham, Mass., is the most marked example of epidotic granite now 

 quarried, though in several other cases, as the biotite-epidote gneiss of 

 Lebanon, K. II., the mineral is frequently present in such quantities as 

 to appear in greenish blotches on a polished surface. Tourmaline gran- 

 ites occur only in veins, and, so far as is known to the writer, never in 

 sufficient abundance to warrant the opening of quarries to work them 

 exclusively. 



In texture the granites vary from extremely fine and homogeneous 

 rocks to those in which the individual crystals are several inches in 

 length. Porphyritic structure is common, and is produced by the de- 

 velopment of larger crystals of orthoclase in the finer groundmass of 

 quartz and feldspar. The color of granites is dependent largely upon 

 the abundance and kind of accessory minerals and the color of the pre- 

 vailing feldspar. Ordinarily the muscovite granites are very light gray 

 in color, the biotite and hornblende granites light to dark gray, or 

 semetimes almost black on a polished surface, as is the case with the 

 hornblende-biotite granite of Saint George, Me. In the red and pink 

 granites the color is due to the red or pink orthoclase. which is the pre- 

 vailing constituent. 



(3) USES OF GRANITE. 



Since the earliest times granite has been used by all civilized nations 

 for monumental and other purposes where great strength or durability 

 was required. But while the enduring properties of. the rocks have 

 caused them to be eagerly sought, their great hardness and consequent 

 poor working qualities have caused them to be used in works of the 

 more simple and massive kind, where but little carving and dressing 

 were necessary. In past ages the cheapness of life and labor in great 

 part counter-balanced these difficulties, and hence are found works of 

 most elaborate design executed in this refractory material ; works which 

 with the present high valuation set upon labor could never be executed 

 but with the aid of greatly-improved machinery and methods of work- 

 manship. The ancient Egyptians, to whom human life and labor were 

 matters of minor importance, have left a profusion of temples, obelisks, 

 and pyramids, whose surfaces are often carved and polished in the finest 

 and most delicate manner, although constructed of material so obdurate 



Hawes Lith. of New Hampshire. 



