BELVIDERE SERPENTINE 441 



The parallel and radiate arrangement may be found in the same sec- 

 tion. According to Rosenbusch, the parallel arrangement is regarded as 

 the chrysotile variety, while the radiate is characteristic of picrolite and 

 the divergent phase of the metaxite variety. The parallel and diver- 

 gent structure is fairly well shown in sections numbers 7 and 57, from 

 pit number 2, United States company. Section 42 shows a very good 

 case of the divergent and interlaced arrangement, while the lamellar or 

 antigorite variety is well illustrated in sections 43 and 58. 



Lamellar and bastite serpentine. — While most of the sections from the 

 serpentine area show the characteristic fibrous aggregates common to 

 thoroughly serpentinized rock, there are in certain sections some addi- 

 tional features, which are believed to throw some light on the probable 

 origin of the original mass. Some of these features are shown in sections 

 51 and 69. It is not uncommon to find a series of parallel laminae mak- 

 ing up an individual crystal. In some cases grains or stringers of mag- 

 netite may be distributed along the partings. In all cases parallel and 

 perpendicular extinction is obtained. These individuals appear like 

 secondary masses derived from an orthorhombic pyroxene, probably 

 some such mineral as enstatite. In other words, the secondary mass is 

 bastite, a pseudomorphous product which is so common in members of 

 the gabbro family. It would thus seem probable that the original rock 

 from which the serpentine was derived was a massive igneous rock in 

 which an orthorhombic pyroxene formed an essential member (see also 

 section 57). 



Discussion as to Origin 



contact phenomena 



The locality yielding the most important facts bearing upon the prob- 

 able origin of the rock from which the serpentine waslderived is the con- 

 tact on the Tucker property. The contact is clear and well denned, as 

 shown in the accompanying photograph of a block (plate 76, figure 1), 

 showing both the serpentine and undoubted amphibolite and the marked 

 line between them. As seen in thin-section, it is very clearly defined. 

 Near the line of junction the serpentine is almost isotropic. When ex- 

 amined, however, in parallel polarized light and under a sensitive tint 

 there appear minute fibrous and block-like individuals, which suggest an 

 actual crystalline structure. At the immediate contact the serpentine 

 assumes, under cross-nicols, a d^ep ultra-blue color. This area includes 

 a part of the absorbed edge of the amphibolite, for the individual com- 

 ponents of the amphibolite may be traced by gradations into the blue 

 areas, where they finally lose their optical characteristics. In other 



