APPENDIX. No. VI. 487 
are told by this author, that the name given to it by the Portuguese, is id 
Presidio (the fortress), and that the natives call it ‘“‘ Maopongu,”— a word 
which, making but little allowance for national difference of expressing the 
same sound in writing, is pretty like that of “ M’wangoo,” synonymously 
added to the sketch given of the Fetish rock by Captain Tuckey. 
Boka M’Bomma, according to the same gentleman’s account, consists en- 
tirely of shistus; but his own specimens from the S., S.E., N-E., and S. W 
parts of that island, are stratified granite or gneiss, in which the feldspar exists 
in very small proportion, and which, on the S.W. side, passes into a beauti- 
fully resplendent silvery variety, stained, towards the surface of the blocks or 
separated pieces, by brown iron ochre, It is in the variety of this gneiss from 
the last-mentioned part of the island, that laminar particles of a dark brown 
colour are seen, some of them exhibiting traces of the regular octohedral form, 
and which appear to be an iron oxydule. There is also, among the specimens 
from Boka Embomma, a fragment of primitive green-stone with embedded 
garnets. 
The specimens from the creek of Banza M’bomma exhibit a mixture of fine 
granular hornblende and quartz; some of them are real hornblende-rock, and 
contain disseminated garnets. These specimens, among which there are also 
some varieties of reddish massive quartz, not unlike milk-quartz, were col- 
lected by Mr. Tudor. 
Besides these primitive rocks, and those from Chesalla, near the Banza, 
which latter affords two varieties of gneiss with black and with yellow mica, 
we have, from the same neighbourhood, and particularly from the Chimoenga 
cliffs, a few specimens of sandstone: it is coarse-grained and ferruginous; its 
colour is grayish, and yellowish, with here and there some purplish specks ; and 
it appears to belong to the oldest formation of this rock. The plain on which 
the banza is situated, is covered by a bed of clay, which, according to a label 
accompanying the specimens, is two feet thick. It is of an ash-gray colour, 
and perfectly plastic. j 
The quartz mentioned by Captain Tuckey and Professor Smith, as being 
found in large masses, on the summit of Fidler’s Elbow, belongs to the variety 
called fat-quartz : the fragments have mica adhering to them, and are here and 
there stained of a blood-red colour. Some specimens of brown-ironstone, 
massive and friable, have likewise been found on this hill. A ticket written by 
