230 EDWARD B. MATHEWS 
and therefore differs from that of the other types. This mesh, 
however, is not as coarse as that in the smaller, probably second- 
ary, microclines present in the same slides, and in the altered 
granites more fully described elsewhere. Perthitic intergrowths 
with albite are not prominent in the majority of the sections, but 
are very abundant in the slides representing some of the 
Fic. 8.—Cripple Creek type of the granite. 
granites from the vicinity of Seven Lakes. The microclines of 
this locality are twinned parallel to the basal pinacoid, according 
to the Manebach law, and differ only in size and occurrence 
from the large and beautiful amazonstone and orthoclase so well 
known from this area. The perthitic lamellae meeting at the 
composition face (001) form an angle of 147° and in each case 
lie a few degrees from the vertical axis in obtuse @ (parallel to 
a steep positive orthodome).* 
‘In color and texture this rock resembles the well-known granite from Red 
Beach, Me., described in the Tenth Census, and it is probable that if similar rock 
can be found where the conditions of quarrying and transportation are favorable it 
will prove of economic interest. 
