328 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
intrusive material is soabundant and widespread, and its metamorphos- 
ing effects through water and magma in various proportions so profound, 
that the phenomena may be said to be regional. 
SUMMARY OF CONCLUSIONS 
The foregoing paper is adapted from a treatise. Notwithstanding my 
endeavors to make the paper short and simple, I find it has become 
somewhat complex, because it has been necessary to make many quali- 
fications to the simple, general propositions. I here repeat some ot the 
more fundamental principles stripped of qualification : 
(1) The chemical alterations which rocks undergo vary greatly under 
different conditions. The more important of these variable conditions 
are water content, temperature, pressure,’and movement. 
(2) The outer part of the earth, of which we have definite knowledge, 
may be divided into two physico-chemical zones. In the upper of these 
the reactions take place with the expansion of volume and with the lib- - 
~ eration of heat, as end results. In the lower the reactions take place 
with contraction of volume and with the absorption of heat, as end re- 
sults. Some of the more important reactions in the upper zone are 
hydration, oxidation, and carbonation; some of the more important 
reactions in the lower zone are dehydration, sulphidation, and silication. 
(83) The alterations under mass static conditions preserve previous 
textures and structures, but may go so far as to completely recrystallize - 
the rocks. The alterations under mass dynamic conditions are different 
in the zone of fracture and the zone of flow. In the former the rocks are 
broken into fragments, and the alterations of the fragments are those of 
mass static conditions. In the zone of flow the alterations obliterate 
previous textures and structures and produce crystalline schists which 
have characteristic textures and structures. 
(4) Rock flow is partly accomplished through mechanical strains, but 
mainly through continuous solution and deposition of the material of 
the rocks by the agency of the contained water. During the flow the 
rock is at all times almost wholly a solid, yet it responds like a plastic 
body to deformation without loss of its crystalline character because of 
the continuous adaptation of the mineral particles, while in large part 
retaining their integrity, to new forms by recrystallization. 
(5) The energy required to produce a given mass deformation in- 
creases downward to the bottom of the belt of granulation. In the zone 
of flow by recrystallization the energy required to produce a given mass 
deformation is less, probably much less, than that in the lower part of 
the zone of fracture. 
