288 ASBESTOS AND ASBESTIFORM MINERALS— MEltlilLL. vol.xvih. 



At the second locality above mentioned, the asbestos (fibrous 

 authophyllite, Analysis 9) occurs along a slickeusided zone between a 

 schistose actinolite rock on the north, and a dark, massive, impure ser- 

 pentine on tlie south. Soil and decomposition products obscure the 

 outcrops, so that observations are limited to an abandoned shaft and 

 a few shallow prospect holes. The evidences of movement are every- 

 where abundant in the form of slickeusided, pinched-out masses of 

 serpentine, sometimes more or less fibrous. The anthoi>hyllite occurs 

 only along the line of disturbance, and in two forms — the one fibrous, 

 asbestos-like, and of a white color; the other also fibrous, but in com- 

 pact masses, with sharp cross fracture, so that tlie material as taken 

 out bears a striking resemblance to a fine-grained hard wood, sawed and 

 split for the fire. The color of this variety is a dull yellowish brown; 

 translucent. By beating, it is readily reduced to a fibrous condition, 

 though the fibers are brittle. On weatliering it appears to undergo a 

 spontaneous fibration quite suggestive of the Balta "amianthus" 

 described by Professor Heddle (ante, p. -80). What the origin of this 

 serpentinous rock ma}' have been, is not liere apparent, but from its 

 locality it seems safe to assume it to be an altered form of the gabbros 

 or peridotites described by Williams.' This being the case, the closing 

 remark nuide by Dr. Williams in his paper, thongh referring to a 

 different locality, is at least suggestive. He says: '• It seems ])ossible 

 that the asbestos deposits of Baltimore County [e. g., like the one near 

 Elysville) may likewise be the results of the alteration of original 

 Ijyroxenic masses." 



Just below the western edge of the lower bridge of the Baltimore and 

 Ohio Railroad across the Patapsco, at this same place, is another, the 

 thu'd deposit, which has come under the writer's observation. This, 

 though small, offers some interesting distinctive features. 



The rock here is a granular, micaceous, magnesian limestone, occur- 

 ring in narrow beds intercalated in the gneiss, and standing nearly on 

 edge, with an approximately east and west strike. As exposed, the 

 rock is locally traversed at varying angles across the bedding Avith 

 sharp joint planes, in some cases so fine as to be scarcely distinguish- 

 able, the walls being in almost perfect contact, or again separated from 

 one another by a slight space, so far as observed never exceeding an 

 inch, and usually much less. The walls of these Joint planes are ver- 

 tically grooved and striated, indicative of a relative movement in this 

 direction, wliieh was, however, presunuibly slight. In nearly every 

 case noted, the walls of these joint planes are sporadically coated with 

 thin fihiis of a pure white asbestos-like mineral, which fills the entire 

 space, and is always arranged Avith its fibers lying in a direction 

 parallel with the striations, or line of movement. Optical examination 

 shows the mineral to be orthorhombic. Chemical analysis (Xo. 40) 

 .shows it to be a mineral of somewhat anomalous composition, and 



1 Bull. No. 28, U. S. Geol. Survey, 1889, p. 59. 



