DETRITIC FORMATIONS 91 
al 
It may also be assumed, that the lowermost horizon of the con- 
‘tinental series in this part of the Republic is represented by a lower 
“permian glacial formation. Probably this was deposited over a per- 
piety levelled surface, consisting of the crystalline schistose and 
q granitic rocks. Already above is stated, that the degradation process 
down to this surface apparently was going on, during a long 
lasting erosion period,! because abyssal rocks are exposed in the 
sal 
surface to a vast extent. This erosion work was naturally accompa- 
‘nied by an uplifting movement of the ground. The plutonic meta- 
morphism, the results of which are now exposed in the surface, 
must thence have occurred a long time before the lower permian. 
The basement cutting plane must thence at least be of pre-per- 
mian age. 
In the Umango area there are remnants of the lower permian 
tillite, as said, only in the Cerro Guandacol profile and at Carrizal. 
‘In all the other localities, where the continental strata are resting 
directly on the basement, either the yellowish sandstone lies lo- 
west, or the red triassic (or cretaceous?) one. The tillite beds (cong- 
lomerate and graywacke) have thence been extensively destroyed 
by erosion before the sedimentation of the red beds, or even be- 
fore the formation of the yellowish sandstone and shales of the 
lower Gondwana. These last named carrying in some parts re- 
mains of a Glossopteris-flora? (Cerro Bola, Cerro Guandacol, Corral 
Martinez) are in the Umango area generally of no great development, 
propably destroyed to a large extent by at least a pretriassic denu- 
dation. The mightiest layers do occur in the Cerro Guandacol profile, 
and a remarkable development is also visible on the southeastern 
slope of the Cerro Villa Union. No other occurrences of these 
1 If this deeply reaching erosion proceeded in all parts of the pampean sierras 
as one phase or was interrupted in some regions by a period of diastrophism, is 
not closer investigated. 
2 According to Kurtz the species Neuropteridium validum should be cha- 
racteristic of the lower Gondwana. 
