C. B. Honcood 8^ A. Wade—The Old Gnniites of Africa, 505 



felspar, and quartz elements, and local developments rich in tourmaline, 

 kyanite, and garnet. The authors state that the crystalline rocks oi 

 the eastern portion of the area described appear to be analogous in 

 every way to the rocks of the same age in Uganda, British East 

 Africa. 



In the discussion on this paper Mr. Walcot Gibson stated that 

 some of the rocks described recalled a sequence in Griqualand West. 

 In this same connexion, some recent papers by Mr. J. Parkinson 

 on the Geology of Southern JN^igeria and Western Liberia are also 

 instructive. Mr. Parkinson,' in describing the geologj- of Southern 

 Nigeria, speaks of a basement-platform of crystalline rocks, and again 

 of a basement - platform of gneiss and schists ; and he divides the 

 crystalline rocks into (1) foliated acid orthogneisses, which tend to 

 lose their foliation and pass into granites, and when coarsely-crystalline 

 have a pegmatoidal habit ; and (2) unfoliated rocks consisting of many 

 varieties of granite, of tourraaliniferous pegmatites, and of aplite-dykes. 

 The petrographical characters of the schists suggest that they were 

 originally sediments. The gneisses arc said to be intrusive in them, 

 but I suspect that later work will show that it is a younger granite 

 which is intrusive in both schists and gneisses. 



Dr. J. W. Evans, in discussing Mr. Parkinson's papers, said that 

 these crystalline rocks showed considerable resemblance to those of 

 Central Africa. 



Dealing with W^estern Liberia, Mr. Parkinson - finds that most of 

 the rocks consist of acid- gneisses (in which biotite is usually the sole 

 ferro-magnesian mineral and microcline is common), garnet-schists, 

 garnet-biotite-gneisses, granitic-orthogneisses, and foliated hornblende- 

 schists, garnet-hornblende-quartz rock, magnetite-hypersthene rock, 

 and chlorite-schists, etc. He states that the probable igneous origin 

 of many of the gneisses and associated rocks is suggested by an 

 exposure at Von on the St. Paul River, where a coarse quartz-felspar 

 vein of pegmatoidal habit cuts clearly across the foliation of the 

 biotite-gneiss, but is apparently an integral part of the complex. 

 He maintains that here also the gneisses ai'e intrusive in the schists. 



As in the Congo Free State Preumont ■* found hDematite and 

 magnetite deposits associated with the old crystalline primary rock, 

 so here, in Western Liberia, Parkinson found hoematite - schists 

 associated with the gneisses. As already noted, Voit^ also found thin 

 beds of haematite and magnetite interbedded between the gneisses on 

 the Limpopo. 



Messrs. Chalmers and Hatch, '^ in describing the geology of 



1 "The Post- Cretaceous Stratigraphy of Southern Nigeria," "The Geology of 

 the Obau Hills (Southern Nigeria)," "The Crystalline Rocks of the Kukuruku 

 Hills (Southern Nigeria)," all" by J. Parkinson:' Quart. .Journ. Geol. Soc, 1907, 

 vol. Ixiii, No. ccli, pp. 308-1". 



= "A Note on the Petrology and Physiography of Western Liberia," by John 

 Parkinson : Quart. Journ. Geol. Soc, 1908, vol. Ixiv, No. ccliv, pp. 313-16. 



■* Loc. cit. 



* " Gneiss Formation on the Limpopo," by F. W. Yoit : Trans. Geol. Soc. S.A., 

 1905, vol. viii, p. 145. 



s "Notes on the Geologv of Mashonaland and Matabeleland," by J. A. Chalmers 

 and F. H. Hatch: Geol. Mag., 1895, Dec. IV,. Vol. II, No. ccclxxi, pp. 193--203. 



