460 SA(WMIES: INR SIMMVBIN IGS 
At Crystal Lake, on Hough’s Peak, Plumas county, California, is a con- 
glomerate that is immediately associated with slate. Slaty cleavage is well 
developed in the latter, and also in the conglomerate. The greater diameters 
of the flattened pebbles are always in the cleavage planes. The harder peb- 
bles are less elongated than the softer ones, and are frequently fractured, the 
fractures being diagonal to the cleavage. 
The probable explanation of the phenomena is that the cleav- 
age develops in the normal planes and the fractures develop in 
the shearing planes, as explained by Becker. At the same depth 
and pressure the softer parts of the rock were under conditions 
of flow and the hard pebbles under conditions of fracture. 
Keith makes the following statement : 
Near Blowing Rock, N. C., is a mashed porphyritic granite in which por- 
phyritic crystals of feldspar are flattened in various degrees, and their 
greater diameters are upon the average parallel with the secondary structure. 
In many cases the feldspar crystals are fractured in a direction diagonal to 
the cleavage, and in some Cases in a single feldspar crystal there are two sets 
of diagonal fractures approximately at right angles to each other and each 
inclined about 45° to the cleavage. 
The phenomena therefore correspond precisely to the idea of 
a pressure normal to the cleavage, which at the same time pro- 
duced fractures in the more rigid feldspar crystals along the 
maximum shearing planes. As in the slate described by Diller, 
the weaker matrix was under conditions of flowage at the same 
depth that the more rigid feldspar crystals were under condi- 
tions of fracture. 
It is a very common phenomenon in slates and schists, both 
macroscopically and microscopically, for the direction of the 
secondary structure to wrap around the harder particles. As a 
hard grain or pebble is approached the cleavage structure in the 
matrix opens out on each side of the grain, envelops it, and 
closes in again beyond it. The structures nowhere intersect, 
although upon opposite sides of a particle near the ends they 
converge, and in passing toward either end they turn and become 
parallel. They would intersect if continued in their original 
direction. While the cleavage of the matrix, where there are 
many harder particles, constantly varies in direction, it nowhere 
intersects. Its average direction is the same as that of other 
