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APPENDIX. No. VI. 
My Dear Sir, British Museum, Nov. 5th, 1817. 
In compliance with your desire, I have examined the specimens of 
rocks that were collected in the late expedition to Congo, and presented by 
the Lords Commissioners of the Admiralty to the British Museum. These 
specimens are all from the banks of the narrows of the Zaire, and are few in 
number ; but they suffice to prove that the rock formation which prevails on 
the banks and islands of the lower parts of the-river is primitive, and greatly 
resembles that beyond the ocean to the west: a circumstance which adds to 
the probability that the mountains of Pernambuco, Rio, and other adjacent 
parts of South America, were primevally connected with the opposite chains 
that traverse the plains of Congo and Loango. As vou have already given, in 
your “ General Observations,” a satisfactory view of the broad geological 
features of the country along those banks, as far as they could be collected 
from the narratives of Captain Tuckey, and Dr. Smith, I shall confine myself 
to a few desultory remarks which offer themselves upon comparing the obser- 
vations of these gentlemen with such of the specimens as have their respective 
localities affixed to them. 
The specimens from the Fetish rocks exhibit a series of granitic compounds, 
in which the feldspar predominates: and most of them, especially the fine- 
grained varieties, contain dissemimated a great quantity of minute noble 
garnets, some of them pellucid, others opaque, and of a reddish brown colour ; 
and all belonging to the trapezoidal or leucite modification. Similar garnets 
also abound in the mica slate of Gombae. A few specimens of a siliceous rock, 
nearly compact, being composed of confluent particles of quartz, mtermixed 
with minute scales of mica, are likewise ticketed as obtained from the Fetishes. 
This insulated group of rocks seems to represent a miniature of the stupendous 
granitic bulwark, which arises from the plain on the north side of the river 
Coanzo, near Cabazzo (the capital of Matamba), and of which an account, 
together with a good representation, has been given by Father Cavazzo. We 
