GEOMORPHOLOGY _ 113 
Ree ver 
affected by the tangential pressure, not only in the immediate vici- 
nity of the gliding planes, but also in the form of a regional ka- 
taclasis more closely described in a foregoing chapter. These dy- 
namical deformations do not seem to extend eastward and outward 
the Umango area. 
ob) A LEVELLING PHASE SUBSEQUENT TO THE TERTIARY FOLDING PROCESS. 
FORMATION OF A MOUNTAIN GRAVEL CONGLOMERATE. 
The above treated tertiary tangential movements have intensely 
affected not only the crystalline schists and the granites, but also 
the sediment cover of the continental series. It has also been sta- 
ted, that these movements belong to an older epoch than the almost 
vertical dislocations now dissecting the Umango area in different 
directions and causing the actual alpine relief. A closer proof of 
this statement shall be made here and it will be clear, that an ero- 
sion phase lies between the two dislocation periods. 
In the middle part of the Sierra de Umango ridge, on the very 
crest line, here at a somewhat lower level than farther southward 
there is a cap of a heavy conglomerate, extending downward on 
the slopes. The conglomerate rests partly on the crystalline base- 
- ment, partly on the steeply inclined sandstone strata of the Pirca- 
»graben“ and of the ,intermontane“ sandstone zone. 
The whole appearance of the conglomerate, the high position 
and the situation in a relatively sunken area of the actual ridge 
and also its great thickness indicates, that it must have formed in 
former times a widespread gravel cover, extending over a more 
continuous surface, but was brought to the actual position and 
extension by a later uplift and subsequent erosion. This erosion is 
still working with great power, and in a relatively short time all the 
conglomerate here will be worn away. 
This conglomerate corresponds doubtless to an erosion phase 
following immediately after the folding-diastrophism. Before a clo- 
ser examination of this erosion and its results is made, it may be 
