41 G REPORT ON NATIONAL MUSEUM, 188G. 



color. Besides biotite, the rock contains small amounts of hornblende 

 and microscopic apatite and zircon crystals.* It takes a good and last- 

 ing- polish, and is well adapted for all manner of ornamental work and 

 general building purposes. The stone has been used so extensively all 

 over the country, that to cite special cases seems superfluous. 



A granite closely resembling that of Vinalhaven is extensively quar- 

 ried at Hurricane Island, some 3 miles distant, in a southwesterly direc- 

 tion, and is used for similar purposes. The structure of the stone here 

 differs in different parts of the quarry. In one portion it lies in com- 

 paratively thin sheets, while in another there occur immense masses of 

 solid rock, extending downward for 50 feet without perceptible jointing. 

 A block of 80 tons has been moved, and a mass 80 by 10 by 25 feet was 

 loosened in the quarry. Natural blocks 500 feet long, 20 feet wide, and 

 50 feet deep occur. 



The celebrated quarries on Dix Island, in Knox County, from whence 

 was obtained the granite for the United States Treasury building at 

 Washington, including the monolithic columns, 31J high by 3 feet in di- 

 ameter, are at the present writing (1885) abandoned. Nearly the whole 

 island has been quarried over and large bluffs entirely removed. The 

 rock is rich in quartz, and therefore quite hard, but is a good and safe 

 working stone. It has been very extensively used in New York City, 

 Philadelphia, and Washington, I). C. 



To give a special description of each and all the quarries of biotite 

 granite to be found upon the coast would extend this work far beyond 

 the prescribed limits. A complete list of them is to be fouud in the 

 Museum catalogue. 



Muscovite biotite granites. — The granite of Augusta and Hal- 

 lo well has long been justly celebrated for its beauty and fine working 

 qualities. It is a fine, light-gray rock, the uniformity of whose texture 

 is often broken by the presence of large white crystals of microcline 

 which inclose small, rounded grains of quartz. Biotite and muscovite 

 occur in abundance, and in about equal proportions, but in small flakes, 

 the muscovite appearing as small, silvery- white glistening particles on 

 a broken surface of the rock. Under the microscope three feldspars 

 are readily distinguished- -orthoclase in imperfect crystals' and irregu- 

 lar grains, an abundance of plagioclase, and microcline in large plates 

 filled with cavities and iuclosures of muscovite and quartz. In the thin 

 sections the quartz iuclosures are usually circular in outline and are 

 pierced in every direction by minute thread-like crystals of rutile, in 

 polarized light showing up in strong contrast with the beautiful basket, 

 work structure of the inclosing microcline. All the feldspars are quite 

 fresh and pure. A few apatite crystals are present, together with occa- 



* In Hitchcock's " r£ei>ort on the Geology and Natural History of Maine," 18G2, p t 

 2G5, the Vinalhaven rock is referred to as a " peculiarly fine-grained syenite of good 

 color," etc. In none of the specimens received at the Museum from this locality, 

 however, does hornblende play more than a secondary part, and in the majority of 

 cases does not appear at all. Hence all are classed as biotite-grauites. 



