286 REPORT OF NATIONAL MUSEUM, 1899. 



hydric acids, like the Saxon "greisen." Others regard them as 

 resulting from the very slow cooling of granitic material injected in a 

 pasty condition, brought about by aqueo-igneous agencies, into rifts of 

 the preexisting rocks. It must be remembered that the high degree 

 of dynamic metamorphism which these older rocks have undergone 

 render the problems relating to their origin extremely difficult. 



Localities. From what has been said regarding occurrences, it is 

 evident that mica deposits are to be looked for only in regions occupied 

 by the older crystalline rocks. In the United States, therefore, we 

 need only look for them in the States bordering immediately along 

 the Appalachian range and in the Granitic areas west of the front 

 range of the Rocky Mountains. 1 In the Appalachian region south of 

 Canada mica mines, worked either for mica alone or for quartz and 

 feldspar in addition, have from time to time been opened in various 

 parts of Maine, New Hampshire, Connecticut, Maryland, Virginia, 

 North Carolina, and perhaps other States, but in none of them, with 

 the exception of New Hampshire and North Carolina, has the business 

 proven sufficiently lucrative to warrant continuous and systematic 

 working. Indeed, were it not for the increased demand lately arising 

 for the use of mica in electrical machines it is doubtful if any but 

 the most favorably situated mines would remain longer in operation 

 in the United States. This for the reason not so much that foreign 

 mica is better as that it is cheaper. 



In Maine muscovite has been mined in an intermittent manner along 

 with quartz and feldspar at the well-known mineral localities at Paris 

 Hill and Rumford, Oxford County; Auburn, Androscoggin County; 

 Topsham, Sagadahoc County; Edgecomb, Lincoln County, and other 

 counties in the southeastern part of the State. In New Hampshire 

 the industry has assumed greater importance. The mica-bearing belt 

 is described by Prof. C. H. Hitchcock as usually about 2 miles in width, 

 and extending from Easton, in Graf ton County, to Surry, in Cheshire 

 County; being best developed about the towns of Rumney and He- 

 bron. The mica occurs in immense coarse granite veins in a fibrolitic 

 mica schist (Specimen No. 63029, U.S.N.M.) of Montalban age, and is 

 found in sheets sometimes a yard in length, but the more common sizes 

 are but 10 or 12 inches in length. Immense beryls, sometimes a yard in 

 diameter, and beautiful large tourmalines occur among the accessory 

 minerals. Mines for mica were opened at Graf ton as early as 1840, and 

 as many as six or eight mines have been worked at one time, though 

 by no means continually. Other mines have been worked in Groton, 

 Alexandria, Graf ton, and Alstead, in Graf ton Country; Acworth 

 and Springfield, Sullivan County; Marlboro, Cheshire County; New 

 Hampton, Belknap County, and Wilmot, Merrimack County, though 

 only those of Groton are in operation at date of writing (1894). 



1 The region of the Black Hills of South Dakota is an important exception. 



