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CRYSTALLINE BASEMENT 97 
4 The abyssal character of the rocks dominates westward to the very 
border of the Andes, where suddenly clastic rocks appear. The 
limit between the crystalline area and the clastic series of this part 
of the Andes may thence be represented by a great fault line. 
A similar contrast exists between the lithological composition of 
the Sierra Pié de Palo and the near lying parts of the Precordillera. 
The rocks forming the area of the pampean underground and 
the „Sierras pampeanas“ and lying under the cover of the conti- 
nental formations, are quite different in their lithology but as mentio- 
ned of a strong metamorphic habit. The age of the various members 
‘is evidently also different. A recapitulation of earlier and later 
_ views on this matter may be justified. 
The first opinion, according to Stelzner (1876) was, that all 
the crystalline rocks outcropping in the „Sierras pampeanas“ belong 
| to the precambrian. This author divides the whole complex into 
two principal lithological groups: 1) an inferior gneissic, intensely 
‘granite intruded and of distinct abyssal character, and 2) a superior 
schistose, of evidently sedimentary origin as a whole and only to 
a limited extent intruded with granite. This Stelzners opinion 
| must be considered quite a correct one, regarding the general litho- 
logy and the relative position of the named complexes. But another 
question arises, when regarding the age of all these rocks. 
According to Stelzners descriptions and sections from the Sierra 
de Famatina it is quite evident, that he considered all the quartzitic 
and argillitic schists of this range as of precambrian age, but that 
the relation of these rocks to the fossiliferous siluric strata of Potrero 
de los Angulos remained an undissolved problem. Concerning the 
discovery of silurian fossils Stelzner says, that he prefers not 
enter into discussion about the fact, that silurian rocks were found 
to the east of the Sierra de Famatina ridge, i.e. far away from the 
Silurian outcrops in the axis of the „Anticordillera“ (today named 
the „Precordillera“*). In order to dissolve this problem Stelzner 
had to few observations. 
