THE 
GEOLOGICAL MAGAZINE. 
MEW SERIES) DECADENV.” VOle Vil 
No. XII.— DECEMBER, 1910. 
ORIG EIN AL ARErteEhmS- 
I.—Tue ReLaTion BETWEEN THE FOLIATED AND NON-FOoLIATED Rocks 
oF SourHERN Nierrta, West Coast, AFrica. 
By Joun Parkinson, M.A., F.G.S. 
CONTRIBUTION by Messrs. Horwood & Wade’ to the 
GeotocicaL Macazinr for November, 1909, calls attention 
(p. 505) to certain papers by me on the relation between the gneisses 
and schists and the later granites of Southern Nigeria. 
Since these papers were published in 1907 I have had the 
opportunity of visiting the western parts of Liberia, a considerable 
proportion of the littoral of the Gold Coast Colony, and on two 
occasions have spent some time in Southern Nigeria. These 
expeditions have served to impress upon me the close resemblance 
existing between the crystalline rocks of these widely scattered 
regions, a resemblance so marked as to suggest a common origin. 
The following notes on the petrology of the Oban Hills in Southern 
Nigeria may throw some light on the relation between the schists, 
the gneisses, and the granites of this part of West Africa. 
A study of the crystalline axis of the Oban Hills shows that, while 
the rocks may be conveniently grouped under certain heads, yet this 
arrangement must remain largely an artificial one. Acid ortho- 
gneisses occupy by far the greater portion of the central part of the 
area, and are, as it were, represented or replaced by a number of 
granite bosses westward in the neighbourhood of the Iyangita, an 
important tributary of the Calabar River. A short investigation 
shows that the gneisses include a variety of types, the mutual 
relations of which prove that they differ in age the one from the 
other to at least some extent. I have grouped these together into 
a single series: firstly, on account of their general petrographical 
similarity; secondly; on account of similarity in habit, e.g. the 
frequent occurrence of a streaky or of a banded structure; and, 
thirdly, on account of the occurrence of special but widely distributed 
petrological types, e.g. a garnet-granulite. 
In addition, comparison of a suite of specimens in the field shows 
that rocks petrographically granites pass by insensible gradations into 
these gneisses. Whatever the agent which produced the foliation 
in the one, it was clearly non-operative during the solidification of 
1 “The Old Granites of Africa.’’ 
DECADE V.—VOL. VII.—NO. XII. 34 
