I A) THE BASIS OF SEDIMENTATION OF THE CONTINENTAL 
| STRATA. 
The sub-Gondwana denudation. 
The great variety of crystalline rocks composing the ,Umango 
structure" plays, as mentioned, the part of a basement supporting 
a mighty series of detritic, continental strata. Evidently a very 
great hiatus corresponds to the unconformity between these two 
lithological elements. It may therefore be assumed, that the denu- 
dation which produced this unconformity, must have been conside- 
table as shown from the great areal exposition of the Famatina ba- 
_ tholith of today, with all its melted and mingled rocks originated 
_ by the abyssal injection phenomena. 
_ The still visible remnants of the basis of sedimentation of the 
~ continental strata in the Umango area and surroundings are pre- 
served only where the overlying strata have been recently re- 
moved by erosion, or where steep, crosscutting profiles are exposed. 
In all other parts the basal plane has been completely destroyed 
_ in consequence of later tectonical disturbances in the region, or it 
is concealed by still overlying strata. The following exposures may 
be mentioned: 1) Arroyo Blanquito, on the western side of the 
Cerro Villa Union to the south. Here the plane is steeply dipping 
_to the SE and overlaid with the lower Gondwana sediments. It 
ee 
2 
appears also on the SE side of this mountain, in the Quebrada de 
los Lagares. Some leagues to the south in the high western profile 
_ of the Cerro Bola, described by Bodenbender (1911), the plane is 
not visible, because hidden beneath piedmont accumulations. 2) Cerro 
~ ee 
