1251 
of granites, intrusive in rocks of probably old-palaeozoic. For in- 
stance by B. P. pr Oniverra, and according to a communication to 
the present writer by GONZAGA pr Campos also in the State of Sao 
Paulo granites have distinctly metamorphosed old-palaeozoic rocks. 
As with the old granites, still too little is known of the petrographic 
features of the Brazilian young granites to compare them with those 
of South-Africa. 
Alkali-rocks. 
First of all we refer to places, where alkalirocks occur at or near 
the opposite coasts, as in Brazil in a number of places in the Serra 
do Mar’) (Itatiaya, Serra do Gericino, Serra de Tingue, Cabo Trio) 
and in Africa near the coast of Liideritzland, and near Cape Cross 
to the North of Swakopmund.®) It is most likely that similar rocks 
occur out of these better known regions in a number of other 
localities near the coasts. We know e.g. already pyroxene foyaite 
from Angola and much farther northward different alkali-rocks, from 
the Los Islands (9°13’ N.East). 
Abyssal-roeks and the related dyke- and effusive-rocks are associated 
with each other. They are in South-West Africa sy enites, nepheline- 
__syenites, essexites, and theralites with phonolites, tinguaites, boston- 
ites, camptonites, monchiquites alnoites. Similar rocks aré known to 
occur in the Brazilian coastal region, we cite only the well-examined 
foyaites, essexites, phonolites, and basic dyke-rovks, besides tinguaites 
and bostonites in and near the State of Rio de Janeiro. The associa- 
tion with the related effusive rocks points in both regions to the 
circumstance that the alkalirocks are in part intrusive into their 
own effusive rocks and that they have crystallized at a small depth 
below the earth’s surface. Erosion caused the volcanoes to disappear, 
which formerly existed near the two opposed coasts of the Atlantic 
Ocean, as they now arise near the Kast-African Lake-region, where 
also alkali-rocks are of frequent occurrence. Farther removed from the 
two coasts alkalirocks exist in various localities. We confine ourselves 
to mentioning only two largest eruptive provinces, hitherto examined 
on both continents, viz that of Pocos de Caldas *) in the South of 
the State of Minas Geraes, and the that of the Pilandsberg *) in the 
district of Rustenburg (Transvaal). These two large provinces, the 
1) O. E. Dersy. On Nepheline rocks in Brazil. 1. c. 
*) E. Kayser. Bericht über geologische Studien während des Krieges in Süd- 
West-Afrika. Abh. der Giessener Hochschulegesellsch. [l, 1920, blz. 18, 
5) O. E. Dersy. loc. cit. 
4) H. A. Brouwer. Geology of the alkali rocks in the Transvaal. Journ. of 
Geology, 1917, XXV, p. 741 sqq. 
