Arthur Holmes — Petrology of North- Western Angola. 229 



3. Barrat, M. "Sur la geologie du Congo francais " : C.R., Oct. 1884; 



Ann. des Mines, p. 379 (map), 1895. 



4. Choffat, P. "Coup d'ceil sur la geologie de la province d ' Angola " : 



Comm. da Dir. dos Trab. geol. Portugal, vol. iii, p. 84, 1895. 

 "Materiaux pour Petude stratigraphique et paleontologique de la province 



d'Angola " : Mem. Soc. Phys. Hist. Nat. Geneve, vol. xxx, No. 2, 1888. 

 Bibliographie giologigue du Portugal et de ses colonies, ser. vni 



(1906-7) ; " Communicoes" du Service geologique du Portugal, vol. vii, 



1909 ; Ser. ix (1908-9), vol. viii, 1911 ; Ser. x (1910-12), vol. ix, 1913 ; 



Ser. XI (1913), vol. x, 1914, esp. p. 17, No. 44. 



5. Cornet, J. " Geologie du Congo occidentale " : Bull. Soc. Beige Geol., 



vol. xi, 1897. 



6. MacHugh, J. J. " Reconhecimento as minas de cobre do Zenza e do 



Bembe " : Boletim de Agricultera — Governo geralda provincia de Angola, 

 No. 6, pp. 265-9, 1909. See also J. F. Barradas. 



7. SOUSA, Pereira de. " Contribution a Petude petrographique du nord 



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Geol., p. 86, 1899 ; p. 353, 1902. 



3. Notes on - the Geology of North- Western Angola. 



As indicated in the adjoining sketch-map, this part of Africa is 

 characterized by three well-marked belts. The middle belt consists 

 of a complex of gneisses and schists through which later intrusions, 

 chiefly of granulitic granite with their attendant pegmatites, and of 

 diabase, have penetrated. On this typical Archaean basement lie the 

 Cretaceous and Tertiary beds of the coastal plain, and the old 

 sedimentary formations which form the plateau of the interior. 



Archcean Complex. — The oldest rocks of the territory, as elsewhere 

 in the equatorial coast lands of Africa, are represented by schists, 

 crystalline limestones, and sediment gneisses. Between the Tertiary 

 beds of Landana and the French frontier at Mayambe, mica-schists, 

 quartzites, quartz-epidote and epidote schists, and felspathic sediment 

 (arkose) gneisses occur, with local bands of chlorite, hornblende, and 

 haematite schists. Generally underlying the schistose rocks, but 

 showing intrusive contacts in places, is a vast foundation of gneissose 

 granites (primary granite gneisses of some authors) with interfoliated 

 hornblende gneisses and anrphibolites. The gneissose granites contain 

 albite, oligoclase, and microcline, an association of felspars which is 

 highly characteristic of the oldest granites throughout Africa. The 

 lithological features of these gneissose and schistose rocks justify one 

 in assigning them to the Archaean. Intrusive into the fundamental 

 complex is a series of granulitic granites which are well exposed 

 near Ncuta. Diabase dykes and sills which have suffered uralitization 

 are found near Ncuta and Belize. The)' appear to be younger than 

 the Palaeozoic sedimentary rocks which appear near the French 

 frontier, for similar diabase intrusions penetrate the old sedimentaries 

 where they cross the Congo to the south-east. In this district, the 

 Belgian sphere of the lower Congo, Cornet has recognized a similar 

 succession. The Matadi schists are intimately associated with 

 gneisses and amphibolites, and the whole complex is intruded upon by 

 the Boma granites. 



