i 
318 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. | 
to the interior deformation of recrystallization is that of the southern 
Appalachians. When inthe Great Valley, we see that the Paleozoic rocks 
are little deformed except by joint-folds and thrust faults. As we pass east, 
deeper into the mountains, the joints and faults become closer together and 
are finally replaced by numerous closely distributed fractures. At the 
same time the rocks show more and more evidence of metamorphism— 
first by granulation, and second by recrystallization. In the cores of 
the mountains are schists and gneisses having well developed cleavage, 
and which have largely or completely recrystallized. In the valley the 
alterations affected but asmall part of the mass of the rock. The deeper 
we went into the mountains the larger was the proportion of the material 
which was affected by the alterations, and in the crystalline schists 
in the core the entire mass was modified, both in a dynamic and a 
chemical way. It is clear in this passage that for a certain distance the 
amount of energy required for deformation per unit mass increased, but 
this tendency may have been reversed in the deepest-seated zone. How- - 
ever, since this latter zone is a region of uplift and the work required for 
the raising of the superincumbent strata must be added to that required 
for the interior deformation of the rocks which we now see, no positive 
statement can be made as to whether the total energy increased or 
decreased per unit mass in the deformation of the deeper-seated rocks. 
The conclusions of the previous pages concerning the energy required 
for a given mass deformation at different depths gives a possible expla- 
nation of the concentration of superficial deformation found in mountain 
ranges. If the energy of deformation is less at the depth at which the 
crystalline schists develop than in more superficial belts, it is possible 
that the more rigid outer shell of the earth may shear over the nucleus 
in the zone at which the crystalline schists develop, the deformation being 
widely distributed. Such shearing for a considerable area may require 
less expenditure of energy than is demanded for the deformation of the 
rocks above; but during the earth movements, as a result of cooling and 
other changes,* the superficial material must certainly be deformed and 
and shortened, and at such places deformation is concentrated and moun- 
tain ranges are formed. Thissubject is, however, far removed from the 
scope of the present paper, and its discussion will be deferred to another 
time. 
MEANING OF ROCK FLOWAGE 
If the argument of the foregoing pages be true, the real meaning of rock 
flowage as deep as observation extends follows as a corollary. 
* Estimates and causes of crustal shortening, by C. R. Van Hise: Journ, Geol., vol. vi, 1898, pp. 
10-64. 
