344 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 15 
Grande do Norte,’ forms the northern edge of the great Archean 
‘‘Brazilian Complex,’’ which consists mainly of granite and gneiss, 
with syenite, quartz porphyry, diabase, and gabbro, as well as various 
schists. There is no record of any areas of alkalic rocks along this 
stretch of coast, but the island of Fernando Noronha, near Cape San 
Roque, is composed of phonolite. The land to the north of the Gulf of 
Guinea, which according to Wegener formerly adjoined the north 
coast of South America, seems to be of rather simple petro- 
logical character, in this resembling the American counterpart.® 
The basal Archean rocks are mostly granite, but we know little of its 
chemical characters. There occur also various other plutonic rocks, 
such as diorite, gabbro, and diabase. Detailed petrographical infor- 
mation regarding this region is rather scanty, but a number of definite 
and significant facts stand out. The granites of French Guinea and 
Dahomey are decidedly alkalic and different from the granites of 
the Guianas. The distinctly sodic tendency of the Nigerian granites 
is shown by the presence of riebeckite and cassiterite, and tourmaline- 
bearing granite occurs in Southern Nigeria. In Nigeria also are 
Tertiary volcanic rocks, among which are phonolite, trachyte, and 
limburgite, and very peculiar, highly sodic lavas, including nephelinite, 
leucitite, and hauynophyre, are found at the Etinde Volcano near 
the coast of British Kamerun. This littoral region has a decidedly 
sodic tendency, quite distinct from that of northeastern South America, 
and appears to be connected with a similarly sodic region to the 
north about Lake Chad and Sokoto. Another feature of this region 
which is not found in the American one is the comparative abundance 
of rocks of the ‘“‘charnockite series” in the Ivory coast, French Guinea, 
and Liberia. These rocks are characterized by abundant hypersthene, 
running from hypersthene granite to norite, and greatly resemble the 
charnockite series of India. It thus seems to be evident that grave 
petrographical and chemical discrepancies exist between the rocks of 
the Guiana-Ceard coast and that of Guinea. 
The igneous rocks of the eastern coastal states of Brazil, from 
Parahyba to Parand, belong mostly to the somewhat monotonous 
Brazilian complex, and are largely granitic, with some syenite and 
pyroxenite (as in Bahia) and dikes of diabase. At various points near 
the coast, in southern Bahia, Minas Gerdes, Rio de Janeiro, Sao Paulo, 
5 Cf. J. B. Harrison, The geology of the gold fields of British Guiana, 1908; J.C. Branner, 
Outlines of the geology of Brazil, Bull. Geol. Soc. Amer. 30: 190-337. 1919, with a geologic 
map. 
6 For some account of the British portions of this region see F. R. C. Reed, The geology 
of the British Empire, London, 1921, pp. 140-155. 
