.">'.' Prof. T. G. Bonney. On the [Nov. 27, 



fragment. My second assistant, Lonis Carrel, who was sent simul- 

 taneously to report upon the northern side of the second summit, 

 brought back from the highest point he reached (about 14,500 feet) 

 the specimen D." (E. W.) * 



A. This is a very dark compact rock, with fairly numerous specks of 

 n greyish felspar, and with occasional minute vesicles. Under the 

 microscope the ground-mass is found to be a glass, in itself almost 

 c-olourless, bat so crowded with opacite as to appear almost opaque with 

 low powers ; in fact its true structure can only be seen in very thin sec- 

 tions and with high powers. In this also minute crystallites probably 

 of a plagioclastic felspar abound. Crystals of the same mineral of 

 larger size are also very frequent ; the larger are often about '02 inch 

 diameter, or even more, but the smaller and more frequent are not 

 much more than one-tenth of that size. The larger crystals resemble 

 in all respects those so often described, and are probably labradorite ; 

 the smaller are lath-shaped, and appear to have smaller extinction 

 angles, and so may belong to one of the species containing more silica. 

 Besides these there are a fair number of crystals of augite, some very 

 well characterised, some containing enclosures of brownish glass. 

 There are also one or two crystalline grains, partly replaced by a 

 secondary dark-brown mineral, which appear to me to be not 

 improbably olivine. There are also some small round specks of a 

 gummy-brown isotropic mineral. It is possible that these are amyg- 

 daloidal and a variety of palagonite. From the above description it is 

 evidently a little difficult to decide whether to retain this rock in the 

 augite-andesites or to term it a basalt, and a chemical analysis would 

 be necessary to settle this point. It is evidently near the border line, 

 but I prefer on the whole to class it with the augite-andesites. 



B. This specimen is a rough scoriaceous lava, weathering a dull 

 reddish to brownish colour ; it is full of small cavities, but in the more 

 compact portions little crystals of light-coloured felspar are common. 

 It is evidently so closely related to A that, as the specimen is in a less 

 favourable condition for examination, I have not had it sliced. Of 

 the two I should more unhesitatingly name this one an augite- 

 andesite. 



C. A very dark compact rock containing fairly numerous specks 

 of a light-coloured felspar. The specimen is a fragment of pris- 

 matic form, having six sides pretty clearly, though -unequally, de- 

 fined. Examined microscopically the ground-mass is seen to be 

 composed of a mass of felted microliths of plagioclastic felsp;r 

 (probably to a large extent oligoclase), with granules of augite and 

 of iron peroxide, most of which are in all probability magnetite. 

 The structure in short is one common in andesites and allied 

 varieties of "trachyte." Probably a little glass remains unin- 

 dividualised, but I have not been able to satisfy myself on this point. 



