110 
G. T. PRIOR. 
consists mainly of fragments of vesicular basalt-glass imbedded in a base of angular 
grains of orange-yellow palagonite with a little magnetite and small felspars ; in parts 
this framnental material is cemented with calcite. In the fraernents of basalt-e;lass, 
all of which have been converted into palagonite, magnetite has separated in fairly 
distinct crystals, and the felspar- laths and olivine-grains which the glass contains are 
fresh and unaltered. 
The tuff from Castle Rock is of similar character ; in the fragments of basalt- 
glass, however, much purplish augite, besides olivine and felspar, has been developed ; 
the felspar also occurs in thin, broad plates as well as in laths. In the basalt-glass of 
the tuff from Cape Crozier, on the other hand, no felspar has been developed, but it 
shows sharply defined crystals of olivine and purplish augite. 
The tuffs from the “ Bare Rocks ” at Hutton Cliffs in Erebus Bay differ remarkably 
from the others in appearance and general character. They are of a dull-green colour, 
Fig. 62. — Kenyte with Poephyeitic Anoethoclase, booldeb from Tuetle Back Island. 
(Natural Size.) 
and are much more compact, so much so that it is not easy with the unaided eye to 
recognise their fragmental nature. They have the appearance of greater age than the 
other tuffs, and show under the microscope that they have been much altered. They 
consist mainly, like the other tuffs, of a very vesicular basalt-glass, but in this case the 
glass has been converted into a dull-green chloritic or serpentinous alteration -product 
instead of into yellow palagonite, and most of the crystals and mierolites of augite and 
olivine have been obliterated ; only rarely is seen a fragment of vesicular basalt-glass 
in which small prismatic purplish augites can be recognised. The tuff contains larger 
fragments of a less glassy non-vesicular basalt, showing under the microscope lath- 
shaped felspars and magnetite in skeleton-crystals, with green altered ferromagnesian 
minerals. 
Kenytes (Trachydolerites, Alkaline-basalts, Rhomb-porphyries). 
From the slopes of Mount Erebus and the islands in Erebus Bay come the 
remarkable rocks mentioned on p. 102. These are distinguished from the basaltic 
