DETRITIC FORMATIONS 79 
the sandstone and the slate of the zone have been intensely torn 
to a mylonitic mass of grayish colour. Following the fault farther 
northward in the direction of the Corral Martinez (lying on the 
eastern border of the zone) there always meet the same lower 
Gondwana rock series, downpressed and torn along the dislocation 
line. In some parts, however, the rocks have remained more un- 
broken and there the original lithology can be studied. In the vici- 
aE: 
Fig. 12. The „intermontane sandstone zone“ (dotted), strongly dislocated. In the background the 
Cerro Villa Union. Sketch from the eastern slope of the Sierra de Umango ridge, toward 
the SE. \ 
nity of the Corral Martinez the writer has observed a vertically in- 
clined part of a clayish slate, apparently a pelodite. The rock ex- 
poses (reminding of the quaternary banded clay in the Baltic basin 
of Fennoskandia) a conspicuous alternation of clayish and sandy 
layers in quick succession. In the sandy layers, (corresponding to 
the „summer“-deposits) I discovered carbonized remains of plants 
with an air of a Gondwana flora. Thinned and torn coal seams 
are outcropping some hundred meters to the south of this locality. 
