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first with a diameter of about 25 to 30 k.m., the second of about 
30 k.m., are both remnants of volcanic centres of large extent. In 
both provinces the effusive-rocks include phonolites, leucite-rocks, 
voleanic breccias and tuffs; among the abyssal-rocks foyaites and 
syenites are known. In both provinces aegirine or aegirineaugite is 
a common dark constituent and tinguaites occur as independent rocks 
or as marginal zone of nephelinesyenites. 
Volcanic rocks and intrusive dolerites. 
The volcanic rocks of the Stormberg-series, whose lavas are widely 
spread over the whole of South-Africa, point to a volcanic episode 
in the mesozoic history of this country. At the same time and 
shortly after this the instrusion of the so-called Karroo-dolorites 
took place, which occur chiefly as dykes and intrusive sheets. Near 
the westeoast the Kaoko-formation, composed of horizontal sandstones 
and augiteporphyrite, extends over a wide area between 18° and 
AS Lad, 
In Brazil similar rocks have a great extent. Dykes and intrusive 
sheets of diabase occur in various places in the states of Minas 
Geraes and Sao Paulo in rocks of permian and of triassic age. Just 
as in South-Africa a thick series of voleanie rock occurs in the 
upper series of the Sta Catherina System, which is the equivalent 
of the South-African Karroo-System. These rocks are considered to 
be of Jurassic age and cover large surfaces in the States of Rio 
Grande do Sul, Santa Catharina, Parana, Sao Paulo and Matto 
Groso, even parts of The Argentine, Urugay and Paraguay. 
Rocks like those in the above-named Kaoko-formation in South- 
Africa occur also in Brazil near the opposite coast in the Southern 
States of Santa Catherina, and Rio Grande do Sul. In both regions 
these formations overlie for the greater part archaean rocks. 
Kimberlites, Alnoites, etc. 
The frequent occurrence of these rocks in South-Africa as far as 
in the Congo State is well-known, in connection with the occurrence 
of the diamond in some of these rocks, especially in some diamond- 
pipes which are generally filled up by a volcanic breccia of 
serpentinised ultrabasic material. 
Suchlike rocks have been known long since in Brazil. They 
have been described by Hussak ') as picriteporphyrite. He points out 
a certain resemblance between the diamond-bearing deposit of Agua 
Suja in West-Minas Geraes and the Kimberlites of South-Africa, 
while later on Kimberlite was recognized in dykes in the State of 
1) E. Hussax. Uber das Vorkomen von Palladium und Platin in Brasilien. Zeitschr. 
f. prakt. Geol. XIV, 1906, blz. 284 e.v. 
