1897 - 98 .] Bocks from the Antarctic Regions. 69 
forms {110}, {010}, and {100}, is brown in the interior, green on 
the exterior, when viewed with rays vibrating parallel to the mean 
axis of elasticity. The spaces between the above-mentioned idio- 
morphic constituents are filled up with allotriomorphic quartz and 
orthoclase. 
The pink varieties of granite owe their colour to the presence 
of fairly large, but for the most part allotriomorphic, individuals of 
pink orthoclase. The well-formed crystals of white felspar, which 
enter so largely into the composition of the grey granites, are com- 
paratively scarce. Hornblende is entirely absent. Quartz is 
abundant, and although never perfectly idiomorphic, it frequently 
indents the orthoclase in such a way as to show that it was in part 
formed before the growth of the felspar had ceased. The most 
important difference between the pink and the grey granites lies 
in the fact that the former are more largely composed of the 
minerals belonging to the second period of consolidation, that is, 
of quartz and orthoclase. 
The tuff is a fine grained, green rock, the true character of 
which can only be determined by microscopic examination. It 
consists largely of crystals and crystalline fragments of water-clear 
felspar. The individuals are generally untwinned, less frequently 
composed of binary twins, and still less frequently striated. Next 
in importance to the felspars are small lapilli of a volcanic rock of 
andesitic character. The section shows also several grains of a 
pale-coloured augite, one of brown hornblende, and some of iron- 
ore. Chlorite, partly in the form of vermicular aggregates, occurs 
as a secondary product, and gives the characteristic colour to the 
rock. 
The fragments of vein-quartz call for no special description. 
They may very well have been derived from the sedimentary series 
which furnished the specimen of radiolarian jasper in which veins 
of white quartz occur. 
2. Cape Adair. 
Two out of the three pebbles are formed of a vesicular olivine 
basalt composed of magnetite, olivine, augite, a basic plagioclase, 
and brown glass. The magnetite occurs in well-formed octahedra 
and in crystalline groups. It is found as inclusions in the olivine 
