474 Prof. T. G. Bonney and Miss C. A. Raisin. 



similar but slightly darker). In the latter, enclosures, probably haema- 

 tite, are rather frequent, which apparently lie in the pinacoidal planes.* 

 We find also some plagioclase felspar, a little pseudobrookite, rutile, 

 and pyrite. The rock has suffered from pressure, which has caused, 

 locally the formation of a chlorite, and possibly of some secondary 

 felspar. 



Another specimen from the same locality seems to be a schistose 

 form of a similar rock. It consists mainly of a blackish, glittering, 

 fibrous hornblende, and thus is very dark green in colour. Its sur- 

 faces are somewhat slickensided and are covered with films of green 

 copper ore. A few elongated grains of clear felspar or quartz appear 

 on microscopic examination, but the slice consists almost entirely of 

 hornblende in rather elongated prisms, with a very definite orienta- 

 tion. This is markedly dichroic, changing through bluish-green 

 (c axis) to grass-green (b axis), or almost colourless (a axis) ; it con- 

 tains occasionally small crystals of rutile, rather impure, arranged 

 along the cleavage planes. A system of parallel planes extends con- 

 tinuously across the crystals of the slice whatever their orientation, 

 roughly making angles of 70 and 110 with the foliation. Even in 

 a grain of (?) quartz lines of enclosures seem to continue the direc- 

 tion of these planes. The rock is now a hornblende schist, but it was 

 probably produced by pressure from one closely allied to a pyroxenite. 



Piedmontite Schist. We come next to specimens of Piedmontite 

 schist, all from near the Gargo glacier. One from the left bank or 

 moraine shows in a rich purple compact matrix a number of dull white 

 spots, rather fragmental in aspect. These exhibit a slight orientation, 

 and traces of divisional surfaces are perceptible, cutting this at an 

 angle of rather more than 35. Quartz, white mica, and piedmontite, 

 the first being the most, the second the least, abundant, and some 

 felspar, are the principal minerals shown in the slice. The quartz 

 contains enclosures, generally minute but variable in size, occasionally 

 with bubbles. The piedmontite occurs in more or less clustered grains 

 or irregular short prisms. With ordinary transmitted light the mineral 

 exhibits a great variety of tints, from rather dull pale orange or straw 

 colour to a rich purplish-pink or strong orange-red, inclining some- 

 times to a burnt sienna, sometimes to a more purple hue. On testing 

 for dichroism, we find in sections parallel to the orthodiagonal the 

 colour changes from pale pink (parallel to b axis) to rich pink (c axis, 

 as stated by Levy), and in sections more or less transverse from pale 

 yellow to burnt sienna, and in some sections from deep amber (a 

 axis)f to a rich pink or slightly orange-purple. 



* These might be similar to the enclosures in schillerised pyroxenes described by 

 Professor Judd, which, however, consist of mixtures of limonite and other oxides. 

 See 'Quart. Jl. Geol. Soc.,' 1885, TO!. 41, pp. 379, 381, 384, &c. 



t ' Les Mineraux des Roches,' p. 184. 



