The Grit. 
225 
ground mass is not homogeneous, and varies not only in com¬ 
ponent minerals but in the size of the fragments. Each grain 
of the structure is clearly seen; then there becomes an individ 
uaiity of structure which contrasts markedly with the confused 
twisted fibrous structure of the light schists. Long distinct 
planes of schistosity are not a feature of the sericite schists, be¬ 
cause of the very nature of the ground mass. Cleavage be¬ 
tween individual flakes is perfect, and while the flakes are 
perfectly oriented they are by no means on continuous planes, 
but are rather twisted into a feltlike mass. So cleavage 
planes are not continuous. On the other hand the coarser 
ground mass made up of crushed grains of quartz does allow 
for the passage of continuous planes. 
Thus it is that the coarser and more brittle rock shows clearer 
evidences of cleavage. Long narrow augen of perfect lenticu¬ 
lar shapes are included in the light sericite schists. These 
augen are now made up wholly of sericite but the outlines of 
the augen are clearly discernible because of the different ar¬ 
rangement and coarser character of the sericite there than that 
in the ground mass. Probably the augen were made up of a 
mosaic of coarser feldspathic fragments, broken down from a 
large inclusion or fragment in the original rock. The coarser 
materials of the augen were altered into coarser and more ir¬ 
regularly arranged flakes of sericite. 
As is so characteristic of these schists there are numerous 
little folds lying diagonally across the schistosity at an angle of 
about 60°. These extend fully across the section and are visible 
at intervals throughout the length of the sections. The crests 
of the folds are from .1 to .2 cm. apart on the average, their 
height is from .03 to .05. The slight puckering of the light 
schist is in sharp contrast to the coarser but more infrequent 
ones of the dark schist. The folds in the latter rock are 
usually at least .5 cm. apart from crest to crest. There will be 
a series of folds and then an undisturbed area of 5 cm. or more 
in breadth followed by a series of folds again. 
The difference in the ingredients of the two rocks accounts for 
this contrast in method and closeness of folding. The sericite 
flakes readily move over each other and quickly adjust them- 
15 
