54 SIERRA DE UMANGO 
rection compared with the general flow direction of the rock. The 
feldspar grains are very altered, and belong probably all to the 
potash feldspar group. In an extreme case of pressure the aplite 
granite, or more exactly the graphic granite, has been torn off to 
a kind of a fine banded rock, like the banded hälleflinta, consisting 
of alternating layers of quartz and feldspar. The structural direction 
is moreover marked by the appearance of parallel biotite flags. 
b) DEFORMATIONS IN THE SEDIMENTARY SCHISTS. 
Among the sedimentary schists of the Sierra de Umango base- 
ment the mica schists are the most affected by the tectonical mo- 
vements. The general habit of these rocks indicates with complete 
evidence, that they must have undergone a strong kataclastic meta- 
morphism. The development of quartz lenses, folds and faults is 
found everywhere, and also microscopically the helicitic structure. 
Especially the abundant manifestations of secondary quartz-lenses 
and layers in all parts of the area are a characteristical feature of 
the powerful dynamical influence in these kinds of rocks. 
A specimen of the lustering mica schist from the western side 
of the high ridge of the Sierra de Umango demonstrates microsco- 
pically a strong folding of the mica planes, conducing in extreme 
cases to the „Slip cleavage“ (Leith). The rock mass between the 
mica planes is composed of small quartz grains. 
The forming of quartz lenses between the schist planes conduces 
to a lenticular structure, a characteristical phenomenon in the zone 
of katamorphism. This phenomenon was evidently a tertiary one 
and not contemporaneous with the granite injections, as the lenses 
never show connection with acid granitic apophyses. Sometimes 
these secondary quartz lenses are thinned out so as to form regular 
layers alternating with the mica planes, thus producing a type si- 
milar to the „Lagenglimmerschiefer“ of Rosenbusch. 
The circumstance, that the mica schist-zones are especially affected 
by the gliding and crushing phenomena, may be explained by assu- 
ya er EAS 
