— 225 ~— 
(76636) Bassalt, Passo Fundo, Rio Grande do Sul. Dark gray to brown gray 
compact and fine-grained rocks, the lighter varieties thickly studded by small 
brown red spots of iron oxide. The microscope shows them to be normal basalts. 
The rust colored spots noted are seen to form borders, or halos, around the 
magnetite granules, indicating a further oxidation of the ferrous iron to the con- 
dition of hematite. 
(76642) Andesite. Passo Fundo, Rio Grande do Sul. A dull brown gray, com- 
pact rock thickly studded with rounded areas of all sizes up to 5 mm. or moro 
tilled with colorless quartzes. 
Under the microscope a dirty brown irresoluble base evidently a partially 
devitrified and decomposed glass, with numerous Jathshaped colorless secretions 
which are too highly altered for satisfactory determination but which were 
once evidently feldspars. Iron oxide and chloritic products abundant. Three 
samples, one of which lacks the amygdaloidal cavities and sbows greenish 
augites and highly altered plagioclase, Evidently an altered andesite. 
(76643) Basalt, Taquarembo, Rio Grande do Sul, A compact dark brown-gray 
rock with one of the constituents sufficiently developed to be determined by the 
unaided eye. Under the microgcope a dense aggregate of clustered augites and 
olivines with lath-shaped feldspars and the usual iron ores. 
(76644) Basalt. Val de Lena, Rio Grande do Sul. Essentially the same as 
No. 76643. 
(76645) Andesite. Dike cutting Coal, Sao Jeronymo Mines, Rio Grande de Sul. 
Dense dull green gray rocks with abundant minute whitish phenocrysts. Under the 
microscope so highly altered that the original mineral composition is determined 
only by the outline of the pseudomorphs. A dense greenish microlitic base 
carrying abundant small phenocrysts of feldspar rarely sufficiently preserved to 
show twin striae or give other than the polarization colors of the same. The 
structure, as a whole, is andesitic rather than basaltic. 
(76646) Basalt, Uruguayana, Rio Grande do Sul. A brown vesicular rock, 
much oxidized but showing under the microscope the normal basaltic composition 
and structure. 
In the state of Sdo Paulo, Dr. Derby finds what he thinks is a 
much younger series of eruptives which resemble ‘‘ash beds’’ and come 
above the great diabase sheets, but the writer did not note any such in 
the states of Parana, Santa Catharina or Rio Grande do Sul. 
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