684 REPORT—1885. 
of a compact, very dark grey rock, weathered externally to a paler 
colour. In it are scattered a fair number of crystals of black horn- 
blende (?) up to about +” in longest diameter. Except for a mere external 
film, the rock is in good condition. 
Under the microscope a clear glassy base is seen thickly crowded 
with microliths of plagioclase felspar, granules and small crystals of 
augite, and granules and grains of magnetite. Four of the larger 
crystals of hornblende are present in the slide; these have a worn, 
corroded look externally, and are black bordered; they are a rich olive- 
brown colour. There are also two crystals of light-coloured augite of 
about the same general size as the hornblende—one with fairly well 
defined angles, not black bordered; the other less perfect, with some 
appearance of a black border; also a smaller one which seems to include 
at one side a fragment of hornblende. The rock is an augite-andesite, 
containing some hornblende of anterior consolidation. 
Rocks from base of Kimawenzi, 15,000 feet (2 specimens ).—Of these rocks 
one is a dark, decomposed, compact rock like 2 (c) ; the other contains 
the same felspar, but is paler in colour. I have not had these cut for the 
microscope, 
Rocks from base of Kibo, 14,000 feet (8 specimens of rocks, 4: specimens of 
minerals.—The rocks are externally a good deal decomposed, and closely 
resemble those from the base of Kimawenzi and from the central 
ridge 2 (c). Ihave had a slice prepared from the one which seemed in 
best preservation. The base is a dark brown glass of rather decom- 
posed aspect, in which are scattered minute felspar microliths as already 
described. There are several small vesicles visible in the slide, together 
with minute circular spots of an isotropic mineral, probably yet smaller 
cavities filled up by some secondary producis. Parts of two of the 
peculiar felspar crystals already mentioned occur in the slide. Externally 
they have a rather rounded aspect, internally there are many inclosures 
of the base. They have a general resemblance to sanidine, but one 
shows rather distinctly a peculiar cross-hatched structure not unlike that 
of microcline. The mineral specimens are all pieces of separate crystals 
of this felspar, which have probably been about the same size as that 
described from the central ridge. They are, I am informed, like it, a 
variety of orthoclase, and some exhibit twinning, the composition face 
being the orthopinakoid. 
Three specimens without any label. Bad specimens of a rock very 
similar to the last described. 
As will be seen from the above notes, the collection of rocks from 
these interesting localities indicates (1) that the highest peaks of the 
Kilima-njaro massif consist of rather basic rocks; (2) that these rocks 
are all of them more or less vitreous, a glassy base having been dis- 
cerned in all that have been examined; (3) that these rocks fall into 
two groups; (a) dark, glassy, or scoriaceous rocks, never showing 
much more than a microporphyritic structure—varieties of augite- 
andesite, more or less glassy; (b) brownish to greyish rather slaggy 
rocks, containing the above-described large crystals of a glassy variety of 
orthoclase. The base is evidently not rich in silica, and does not, I 
suspect, materially differ from that of the other group, so that I should 
regard these as intermediate between the normal augite-andesites and the 
normal sanidine-trachytes, and name them provisionally orthoclase-bear- 
ing augite-andesites. Mr. Johnston’s collection is, I think, sufficiently ex- 
a 
