69 
trending west, which has thrown the overlying beds into a 
series of simple folds: an anticlinal directly conforms with 
the surface of the eruptive, and consists of blue garnetiferous 
schist and gneiss, with "eyes" of felspar, large crystals of 
hornblende and fractured garnets. South of this spot the 
overlying beds of gneissic quartzite can be traced, occurring 
as two perfect sigmoidal folds, the second synclinal, with a 
very sharp angle, thence passing to a shallow monocline that 
is finally lost in the zone of crushing at the contact with a 
second intrusive mass. The extreme southern exposures of 
the range occur as outlying masses of gneissic rock, the strike 
of which agrees with that of the country, and the dip is 
southerly. 
At the foot of Mount Cockburn, a low outlier of the same 
exposures consists of quartzitic grneiss, the foliation being im- 
perfectly developed, and large, lenticular "augen" of felspar 
not infrequent. The hill shows perfect parallel planes of 
jointing in direction N., 15° W., dipping 75° westerly. 
These planes are made the more conspicuous by the resulting 
fissures having become filled with detritus, in which a thick 
growth of grass and other vegetation, standing out as dark, 
prominent lines from the light-coloured gneiss behind, has 
flourished. 
To the north the augen gneiss merges on the one hand 
into a gneiss with linear foliation, and on the other into a 
crushed rock, with large, false ''pebbles" of quartz, produced 
from the original rock, surrounded by well-marked, concen- 
tric ''lines of flow" of crushed material. Shearing and com- 
pressive stresses have certainly contributed largely to the for- 
mation of the latter, and like forces have produced the augen 
gneiss, while the ultimate result of rock-crushing and shearing 
is the finely "lined" variety of gneiss. 
Striking evidence of the extreme conditions of stress that 
existed during the mountain-building processes is afforded at 
the north-eastern end of the Mann Ranges in the form of a 
series of step-faults on a fairly large scale. The country here 
consists of compact gneiss, with large, bluish orthoclase and 
folia of biotite, intruded by diorite dykes. Ten distinct, 
almost vertical, scarp-faces of gneiss, rising one above the 
other, can be seen, each surmounted by the severed portions of 
one and the same diorite dyke. The igneous rock, four feet 
in thickness, forms the floor of each step, the vertical dis- 
tances between the successive steps averaging twelve feet, 
and each fractured mass of the diorite dyke dipping about 
10° S. The several fault planes hade 10' in a direction X. 
10° E. 
