300 REPORT OF NATIONAL MUSEUM, 1899. 



Mode of occurrence and origin. Concerning the associations, occur- 

 rence, and origin of the fibrous structure of these minerals existing 

 literature is strangely silent. It is known that all occur only in regions 

 occupied by the older eruptive and metamorphic rocks. It is prob- 

 able that in the fibrous forms the mineral is always secondary, and the 

 fibrous structure due in part, at least, to shearing agencies; that is, to 

 movements in the mass of a rock whereby a mineral undergoing crys- 

 tallization would be compressed laterally and drawn out along a line of 

 least resistance. This is, however, not the case with the fibrous varieties 

 of serpentine, which undoubtedly result from the crystallization in 

 preexisting fractures, or gash veins, of the serpentinous material. 

 The process is evidently the same as that which is seen in studying, 

 under the microscope, thin sections of olivine-bearing rocks which 

 have undergone hydration. The asbestos in Alberene, in Albeinarle 

 County, Virginia (Specimen No. 62550, U.S.N.M.), occurs in thin, 

 platy masses along slickensided zones in the so-called soapstone 

 (altered pyroxenite) of the region, the fibers always running parallel 

 with the direction of the movement which has taken place. At 

 Alberton, Maryland, the fibrous anthophyllite (Specimen No. 62604, 

 U.S.N.M.) occurs along a slickensided zone between a schistose acti- 

 nolite rock and a more massive serpentinous or talcose rock, which 

 is also presumably an eruptive peridotite or pyroxenite. The fibration 

 here runs also parallel with the direction of movement as indicated by 

 the slickensided surfaces. 



Localities. As already stated true hornblende asbestos occurs only 

 in regions of eruptive and metamorphic rocks belonging to the paleo- 

 zoic formations. The same is true of anthophyllite. Fibrous ser- 

 pentine occurs sporadically with the massive forms of the same rock 

 which is, so far as known, almost invariably an altered eruptive. The 

 three forms are therefore likely to occur in greater or less abundance 

 in any of the States bordering along the Appalachian system, but are 

 necessarily lacking in the great Interior Plains regions, reoccurring 

 once more among the crystalline rocks of the Eocky Mountains and' 

 the Pacific coast. The principal States from which either the true 

 asbestos or anthophyllite has been obtained in anything like commer- 

 cial quantities are Massachusetts, Connecticut, New York, Maryland, 

 Virginia, North Carolina, South Carolina, Georgia, and Alabama, 

 though it has been reported from other Eastern as well as several of 

 the Western States. Fibrous serpentine (chrysotile, or amianthus) 

 occurs in small amounts at Deer Isle, Maine; in northern Vermont; at 

 Easton, Pennsylvania; Montville, New Jersey; in the Casper Moun- 

 tains of Wyoming, and in Washington. It is known also to occur in 

 Newfoundland. The chief commercial sources of the material are, 

 however, Canada and Italy. The Canadian source is in a belt of ser- 

 pentinous rocks extending more or less interruptedly from the Ver- 

 mont line northeastward to some distance beyond the Chaudiere 



