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These eruptive beds begin at 738.2 meters above tide, near the 20th 
kilometer from Minas, and succeed one another in sheets (some of 
which exhibit the columnar structure) of 20 to 50 metersin thickness 
up to 1850 to 1400 meters in the summits of the Serra Geral, 25 
kilometers distant from Minas. 
It isthe presence of these eruptives in such bold relief that ren- 
ders the ascent of the Serra Geral so difficult at most points across 
Santa Catharina and Rio Grande do Sul, since the rapid erosion of the 
streams cuts away the softer underlying Triassic and Permian heds, 
and thus tends to perpetuate the almost vertical face of the eruptives, 
This ancient scismic activity which poured out over South Brazil 
such immense masses of eruptives appears to have been contempo- 
raneous with the outflows of doleritic diabase and basalt which penetrate 
the Triassic beds of South Africa, India, and elsewhere in the southern 
hemisphere and may also have been contemporaneous with the great 
eruptions wich followed the close of the Triassic period in the northern 
hemisphere. 
The effect of these dikes of diabase upon the adjacent strata in 
the way of metamorphism from heat is not very great. The sill of 
diabase nearly 2 meters in thickness which was intercalated between 
the Barro Branco coal and an overlying sandstone on Rio Passa Dois 
in Santa Catharina, merely reddened the sandstone, and gave the 
plant remainsin the accompanying roof shales of the coal an anthra- 
citic appearance. 
The vertical dike found in the mines of the S. Jeronymo Company 
in Rio Grande do Sul has affected the coal hy partially coking it for 
only 3 to 4 meters distant. 
Where sandstones in contact with diabase were nearly pure 
silica, they were partially vitrified, but when they contained much 
aluminous material, very little change can be noted. 
The occurrence of these dikes will not interfere seriously with 
coal mining operations in Santa Catharina or Rio Grande do Sul, 
except where the surface gives very distinct evidence of their pres- 
ence, since otherwise the dikes are thin and of small importance. 
Not much time was available for the field study of these interesting 
eruptives, but a few samples of them were collected, and submitted 
to Dr. G. P. Merril, the accomplished Head Curator of Geology in 
the United States National Museum, Washington, D. G., who has 
kindly prepared the following notes upon the samples in question. 
