SEPT. 19, 1923 WASHINGTON: COMAGMATIC REGIONS 345 
and probably in Espirito Santo, highly sodic rocks occur, including 
trachyte, phonolite, tinguaite, limburgite, jacupirangite, and nephe- 
lite syenite. The rather extensive occurrence of monazite sands 
along the coasts of Bahia? and Espirito Santo indicates the presence 
of sodic syenitic rocks in the hinterland. The islet of Trindade, about 
1300 kilometers east of the coast, is composed of phonolite, according 
to Branner;’ this occurrence is probably comagmatically connected 
with that of phonolite at the Island of Fernando Noronha off Cape 
San Roque. South of Brazil phonolitic rocks occur in Paraguay and 
possibly in Uruguay and eastern Argentina. ‘The occurrence of vast 
sheets of plateau basalt in Parand and other southern states of Brazil 
and in Argentina will be discussed later. 
Along the west coast of Africa, south of Guinea, and opposite Brazil, 
. Uruguay, and northern Argentina, the dominant igneous rocks appear 
to be mostly granitic and gneissose, belonging to the African ‘‘funda- 
mental’ complex.’’ Although comparatively little is known of this 
stretch of coast yet here and there some occurrences of possibly sig- 
nificant rocks are known. Thus, trachyte, phonolite, and trachydol- 
erite are found on the island of Sao Thomé and they are also probably 
represented on Fernando Poo, where the lavas are mostly basaltic. 
These islands lie in the Bight of Biafra at the northeast angle of the 
Gulf of Guinea where Cape San Roque would fit in. Sodic lavas, 
aegirite trachyte, phonolite, and nephelinite, occur in Angola, as well 
as a series of sodic plutonic rocks, including nephelite syenite and 
shonkinite. Representatives of a fairly well-defined charnockite 
series; ranging from hypersthene granite to norite, are met with in 
Benguela. Neither sodic nor charnockitic rocks seem to have been 
found farther south in the Southwest Africa Protectorate. In the 
Transvaal there are large areas of nephelite syenite and other sodic 
rocks described by Brouwer, Shand, and others; but these would appear 
to belong to the Indian Ocean region rather than to that of the Atlantic. 
There are thus found on, both sides of the Atlantic, southward from 
Cape San Roque on the west and from the Bight of Biafra on the 
east, lines of isolated occurrences of sodic rocks, both plutonic and 
voleanic, which have been intruded into or poured out over continental 
basement complexes of apparently quite similar granitic and gneissose 
rocks. Alkalic, chiefly sodic, rocks occur also in the intervening 
Atlantic, as at Fernando Noronha and Trindade near Brazil and at 
Ascension and St. Helena in the southeastern Atlantic. This corre- 
71 found monazite sand at a bathing beach near the city of Bahia, but observed no 
syenite in the prevailingly diabasic rocks of the neighborhood. 
§ J. C. Branner, Bull. Geol. Soc. Amer. 30: 300. 1919. 
