CRYSTALLINE BASEMENT 19 
4 of the sedimentary types, that the quartzitic and mica schists occupy 
Pe. > = 
: the lower, the great limestone banks the higher stratigraphical levels. 
‘a 
E72 
The question about the relations of the Umango sedimentary 
series to the geological structure of the surrounding countries and 
the problem of the age of these rocks will be treated of below. 
Discussion of the Geology of the Umango „pregranitic“ sedimen- 
tary pile. | 
As seen, the series are composed principally of three types 
of rocks, representing the three principal members of products 
of subaerial decomposition by chemical way: lime, silex and argile, 
with some transition products especially between the two later. It 
may be presumed, that the basement of the sedimentation was gra- 
dually sinking, because the limestone banks occur in the higher 
_ horizons. The continental surface, from where the decomposed 
material derived, was probably an ancient one, composed of acid 
‘silicate rocks, as for instance the old precambrian terranes. It is 
_ probable from the heavy masses of quartz-sediments in the Umango 
area, that many acid rocks really occurred in this terrane. The 
complete lacking of conglomeratic layers in the Umango series and 
also of other traces of stratigraphical breaks makes it very probable, 
that the sedimentation proceeded quite uniformly. 
Above was stated, that in consequence of the intense metamor- 
phic changes in the Umango series it is impossible to determine 
the age of the rocks by way of fossils. One will arrive at a defi- 
nite conclusion with this question by comparing the Umango rocks 
with others occurring in the neighbourhood. 
Above it was already stated, that the schists of the Umango 
area show a great resemblance with the similar metamorphic schists 
oi the Nevado de Famatina. Whilst the last are considered by 
Bodenbender of cambrosilurian age and are intruded by the 
same granite (the Famatina batholith), both in the Umango and in the 
- Famatina, and older granites do not appear in the Umango, it seems 
