MASS DYNAMIC ACTION. 299 
It has been noted that in the production of the characteristic texture 
and structure of the crystalline schists, that the original textures and 
even structures may be destroyed, whether they be those of sedimentary 
or igneous rocks. In passing from an areaof molecular dynamic action 
to an area of mass dynamic action all stages of obliteration of the orig- 
inal textures and structures and the development of the new textures 
and structures may often be traced. In an intermediate stage the larger 
particles or more refractory minerals may show the textures of the orig- 
inal rock, the matrix of the same rock, however, having the texture of a 
recrystallized rock. In instances of extreme alteration no trace of the 
original texture remains even in those cases where the rocks were coarse 
conglomerates or coarse porphyritic igneous rocks, and the secondary 
structure may traverse the original structures or the latter may be wholly 
obliterated. 
Thus mass dynamic action stands in sharp contrast to molecular 
dynamic action, in so far as textures and structures are concerned. By 
mass dynamic action there is a tendency to destroy old textures and to 
produce a characteristic texture the more important features of which 
are mineral particles of uniform size and parallel orientation, and there 
is a tendency to destroy old structures and to produce a characteristic 
slaty or schistose structure. Under conditions of molecular dynamic 
action the original textures and structures are preserved, although they 
may be somewhat modified or. emphasized by the unequal size and lack 
of orientation of the mineral particles. 
Theory of recrystallizaton.—In the process of recrystallization all the 
forces described (pages 275-277) are at work. 
In the deep-seated zone where the process occurs the temperature is 
considerably higher than at the surface, because of the increase of tem- 
perature due to depth, because of heat resulting from mechanical action, 
and in many districts because of heat derived from intrusive igneous 
rocks. Water occupies all the openings to those of subcapillary size. 
Moreover, this water has about the temperature of the adjacent rocks, 
and is therefore extremely active. ‘Taking the ordinary gradient, the 
temperature at a depth of 3,000 meters would be 100° C., at 6,000 meters 
200° C., and at 9,000 meters 300° C. At these temperatures the material 
would ordinarily be water and not steam, for the pressure of the super- 
incumbent column of water is more than sufficient to prevent it from 
passing into the condition of a gas. However, as a result of the heat of 
mechanical action or of igneous intrusion, or both, the temperature at a 
given depth may become so high that the water may at least locally and 
for short times be in the form of water vapor. 
As a result of the mechanical forces the mineral particles are either 
