234 



Prof. T. G. Bonne}'. 



ary origin. Rock fragments are not common in the first (interior) 

 specimen (vii) ; one, however, is probably an altered shale, and another 

 possibly a limestone. This is bordered by a pale, pyroxenic mineral 

 piercing into the grains of calcite. In the second specimen (vi) frag- 

 ments are rather common ; among them are those of diabase, ranging 

 from fine to coarse, one specimen of the latter, originally, perhaps, an 

 inch in diameter, showing an ophitic structure ; felspar and augite both 

 being rather altered, seemingly by infiltration, and one small fragment 

 resembles a subcrystalline limestone. Specimen (v) does not materially 

 differ, but seems to contain more carbonate than the others. The dark 

 streaking is due to grains of iron oxide or serpentine with much opacite ; 

 rock fragments are few and small. Specimen (iii) from the thin vein 

 contains a few very small rock fragments, mudstone or shale, more or 

 less altered, possibly also a compact diabase. The " country rock " is a 

 mudstone, consisting of small chips of quartz and felspar, variable 

 in size, embedded in a dusty matrix, including a carbonate, which is 

 more abundant within about a fiftieth of an inch from the junction. 

 This part is slightly stained, but I was unable to detect any signs of 

 contact metamorphism. Specimens (ii) and (iv) are generally similar, 

 but the former contains some small rounded bits of varieties of diabase, 

 and one may represent a crystalline limestone. The veins are filled 

 with calcite and other secondary products, and are bordered by a very 

 thin film of a brown micaceous mineral, like that described as often 

 permeating the "blue." Both specimens suggest micromineralogical 

 changes, such as might be produced by the passage of hot water. 



Other specimens of the sedimentary rock in the immediate neigh- 

 bourhood of the blue have been forwarded to me by Mr. Trubenbach. 

 One, from the adit on the southern side of the section mentioned above, 

 is a grey mudstone, containing a flattish rectangular pebble, of a dark 

 green compact rock. Two others are from No. 2 mine, or about 700 

 yards to the south-west. One, struck in the shaft at a depth of 200 feet, 

 is a conglomerate, composed of well-rounded rock fragments, with some 

 scattered grains of quartz. Each of the former is bordered by a zone 

 of a crystalline carbonate (impure calcite), and the interstices are 

 filled, sometimes by a clearer variety of the same, but more often by 

 some minutely granular secondary product. Of the rock fragments, one 

 is a subcrystalline dolomitic limestone ; two, perhaps, are chalcedony; the 

 remainder are igneous ; the majority being varieties of diabase, some- 

 times rather decomposed ; the rest trachytes, mainly andesites. Their 

 general aspect and the not unfrequent presence of vesicles (now filled 

 with viridite) suggest that they have been furnished by lava-flows. 

 Another specimen, obtained in the same working at a depth of 400 feet, 

 is a rather f elspathie diabase, not unlike one of the varieties in the 

 conglomerate. It is a good deal decomposed, is not improbably from 

 a lava-flow, but does not call for a minute description. 



