50 SIERRA DE UMANGO 
The structures of the white intrusives, occurring more to the west - 
(in the high ridge of the Sierra de Umango etc.), will be treated of - 
later on, as they all belong to secondary structures of Öyramira 
origin, caused by the tertiary movements. 
D) KATACLASTIC STRUCTURES OF THE BASEMENT ROCKS, 
PRODUCED PRINCIPALLY BY LATER (TERTIARY) 
OROGENETIC MOVEMENTS. 
As will be shown! later on, the whole Sierra de Umango area | 
was affected during tertiary times by orogenetic movements. In an 
earlier phase these manifested themselves by a tangential pressure 
from the} west, causing am. o. the folding-tectonic in „the inter- 
montane zone“. It will also be shown, that the Umango area forms 
a part of „Foreland“ or „avant pays“ to the andean chain. 
These eastward pushing tangential movements produced not only 
different disturbances in the continental sandstone cover. The — 
crystalline basement was also strongly affected and a regional kata- 
clasis developed in it. The following petrographical description 
may be a study of the crushing phenomena of the rock minerals, 
referring to the well known researches of Leith.” 
It might be supposed, that some of the below described secondary | 
structures may originate from an earlier diastrophic period than 
the tertiary, for instance, from the same phase, when the white 
granite was intruded. It seems, however, probable, that the kata- | 
clasis developed during this period, was brought to recrystallisa- 
tion by the subsequent intrusion of the white granite. 
The tertiary tangential pressure released along NNE running over- 
thrust planes and broke up the Sierra de Umango crystalline base- 
1 Tertiary tectonics, in Part II. 
1905. 
2C.K. Leith, Rock cleavage. U. S. Geol. Survey. Bulletin 239. Washington 
