34 SIERRA DE UMANGO 
tains biotite megascopically visible in small torn spots, irregularily 
scattered through the rock mass. Microscopically (see Plate II, fig. 2) 
there are proois of a strong kataclasis, with the most intense — 
granulation of the quartz component, the last as a kind of cement 3 
filling up the spaces between larger fragments of feldspar. This q 
latter mineral is viz. lesser crushed than the quartz, an usual phe- 4 
nomenon of the kataclasis processes of quartz-feldspar rocks. The 4 
dynamic influence is also shown by the development of an undu- 
lating extinction of the feldspar, frequently in association with a 
„undulating perthite“, especially in the more elongated corners of i 
the mineral. Generally it seems to be a plagioclase, although 2 
a closer determination is impossible. Mafic minerals are present to — 
a small extent, essentially minute biotite spots. 
This extremely crushed granite seems to be very common in the 
Sierra de Safiogasta, and also in other parts of the granite body ~ 
according to the observations of Bodenbender (1916). The corres- 
ponding dynamic processes probably occurred during the tertiary — 
diastrophic periods. 
In the above mentioned Quebrada de Tambillos on the western 
slope of the Nevado I discovered also a finegrained aplitic type. 
The quartz appears in handspecimen dark and well individualized, 
and the feldspar has a reddish colour. Mafic minerals seem to be 
completely absent. No microscopical examination were made of this 
rock. It develops distinct contact lines to the surrounding types of 
granite, and may perhaps be of a somewhat younger date. 
Regarding the occurrences of porphyric varieties in the batholith © 
Bodenbender (1916) mentions a quartz porphyric type from the 
highest part of the Nevado. I know also such specimens from my 
route over the Pampa and Tocino passes. Their occurrences may — 
possibly correspond to a higher crustal horizon, because there are - 
in the vicinity fossil bearing rocks of the intruded schist mass. 
A granite type with great feldspar phenocrysts (granite-porphyry) 
extends over some wider areas on the eastern part of the intrusive 
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