278 PROCEEDINGS OF THE AMERICAN ACADEMY 



cracks in the feldspar, and is clearly the light-green, soft substance 

 already mentioned. The larger sheaves, occupying the whole thickness 

 of the thin section and the veins, permit some optical determinations 

 on the mineral. Examining it with the polarizer, it shows a marked 

 dichroism, being deep bluish-green, when the longer axis of a needle 

 coincides with the shorter diagonal of the nicol, and light, faintly brown 

 or greenish-brown when at 90". Between crossed nicols some of the 

 needles become dark when the longer axis is pai-allel to a nicol-plane ; 

 but there often appears to be an angular difference of several degrees. 

 It seems, therefore, considering its softness under the needle, and its 

 optical qualities, to be possibly a monoclinic chlorite. Wliere th(5 

 change has gone very far, only fragments of the feldspar remain, sur- 

 rounded and penetrated by the chlorite and granular quartz. 



One or two crystals were seen having the contours of feldspar indi- 

 viduals sharply defined, but consisting of granular quartz, showing 

 aggregate polarization, and containing apatite needles and the chlorite. 

 They appear to be pseudomorphs of quartz after feldspar. Witii the 

 chlorite occurs a yellowish-green chloritic mineral, consisting of closely 

 packed minute spheres, made up of spicules or folitc, radiating from a 

 centre ; they are double-refracting, but show no absorption. 



As a rule the augite crystals have disappeared, as such ; but, in places, 

 individuals are observed which are in one part perfectly fresh, and in 

 others show the stages of change. Where fi-eshest, they are transparent, 

 almost colorless, with a smoky tinge, and have many irregular fractures, 

 and, in places, parallel cracks, indicating cleavage. 



AVhere they are apparently perCectly fresh, the principal foreign 

 particles they contain are minute ones of a bluish-gray color or, in the 

 larger grains, deep sapphire-blue, and have a narrow, dark rim. These 

 are often in sharply defined rhombic prisms, but more generally of 

 irregular shape, and sometimes connected by hair-like necks. They 

 are almost always arranged in warped planes, in some of which they 

 are much scattered, in others closely packed. A linear arrangement 

 was also observed. 



Besides these, the pyroxene contains slender straight rods, which are 

 opaque and black, possibly because of their slender proportions. They 

 are in groups of parallel rods, two groups in places, intersecting each 

 other, and eacli group being parallel to a different axis. These grou^js 

 of rods become in places the skeleton of a curious structure ; the rods 

 in parallel rows being connected by a bottle-green substance, so as to 

 form parallel uneven planes, like brush-fences, in which the rods repre- 

 sent the posts, and the bottle-green substance the brush, interwoven hori- 



