The ''Augeir -Gneiss Area. — Luf/iicr aiul Hies. 255 
lies, therefore containing much feldspar, such as a granite or 
aplite. The result of the metaniorphic action seems to have 
been the production of agneissic structure caused by pressure, 
together with a granulation of the minerals resulting from 
shearing, the unsheared portions of the rock remaining as 
" augen." The evidences of this metamorphic a(!tion appear 
as strains, bending, breaking and wavy extinction in the lar- 
ger individuals, and in the granulation of the other consti- 
tuents. This idea of the origin of •' augen '^ structure based 
entirely on crushing and shearing, seems to be also held by 
Kemp, Callaway, Lehmann and others as already noted. 
There is nothing to prove that the strains in the -'augen" 
occurred subsequent to the forces which produced the crushed 
groundmass. 
Concerning the porphyritic aspect assumed exclusivel}^ by 
the feldspar, two theories suggest themselves: 1st. involving 
the idea of segregation advanced by N. H. Winchell and 
J. G. Goodchild, both already mentioned; and, 2d, that the 
quartz being more brittle than the feldspar would crack more 
easily, although it might be urged that the feldspar would 
give way first on the account of its cleavage.* The fu- 
sion point of quartz being far above that of orthoclase the 
latter might become softened by the heat, produced by dyna- 
mic action, while the former was still hard and brittle. The 
softened orthoclase would then accommodate itself to tlie 
strain of shearing by being drawn out. 
While this latter theory is at variance witli that i)ut fortli 
by Lehmann. for the formation of feldspar '-augen" in the 
Saxon granulites, it does not seem quite manifest how a piece 
of feldspar could be pulled out into a lenticular shape witli- 
out being first softened (but not necessarily fused). Further- 
more it would not seem that the presence of cracks is a posi- 
tive proof against a former softened condition of the feldspar 
*In this connection it is well to remember that the theoretically i>er- 
fect cleavage of feldspar is often only made apparent, by the rending 
effect of grinding, in very thin sections. 
