1249 
chroie amphibole, the colour ranging from dark brownish green to 
light brownish yellow, without large extinction-angles; of ore, 
cancrinite, analcite, fluorite and little calcite. 
Trachyte. 
The grey, compact rock was collected from a lava flow more 
than 100 M. in thickness, near the facenda D. Eugenia. 
A microscopic examination shows beside portions, in which crystal- 
line constituents with weak birefringence are scarcely visible, other 
parts, in which distinctly felsparlaths without polysynthetic twins 
and with nearly parallel extinction, have been largely developed. 
There are also larger felsparcrystals; in sections normal to the acute 
bissectrix they present a rather small axial angle. Some of the larger 
felspars exhibit polysynthetie twins with small extinction-angles. 
Parts with a more or less regular form and consisting of muscovite 
flakes remind somewhat of liebeneritepseudomorphs after nepheline. 
However, sometimes quartz occurs in large quantity mixed with 
muscovite flakes. The quartz, which we take to be a secondary 
product, also occurs scattered in the rock. Finally pyrite must be 
mentioned as one of the composing minerals. 
Resemblance between the Eruptive Rocks of Brazil 
and those of South Africa. 
Rocks, rich in alkalies, some of which have been described above, 
are of frequent occurrence in Brazil as well as in South-Africa, and 
the various types in both regions show many points of resemblance, 
which will be discussed in detail lower down. This resemblance 
exists also with regard to other eruptive rocks. On a journey through 
Brazil in 1920 I was struck by the marked resemblance of some 
groups of sedimentary rocks with which [ got acquainted in South 
Africa in 1910. Anyhow the differences are not greater than are 
known for adjacent regions of the African continent at a much 
shorter distance. 
As the principal groups of eruptive rocks whose resemblance in 
composition and geological aspect will be discussed below, we mention: 
1. Old granites, intrusive in rocks of probably archaean age. 
2. Younger granites, intrusive in deposits of Devonian age and 
older than permo-carboniferous rocks. 
3. Younger rocks, rich in alkali, (nephelinesyenites, aikalisyenites 
with accompanying abyssal- and effusive rocks). 
4. Jurassic volcanic rocks and intrusive dolerites (the determination 
