MOLECULAR DYNAMIC ACTION. 291 
Williams and Bascom,* which are completely devitrified. In the papers 
of these authors many similar instances are cited. 
REORYSTALLIZATION OF MINERALS UNDER MASS STATIC CONDITIONS 
To the metasomatic recrystallization of minerals the same principles 
are applicable as to the devitrification of glass. The chief difference is 
that the process of solution and re-deposition is presumably slower upon 
the average for minerals than for glass. The original molecular arrange- 
ment is closer, more regular, and harder to break up. 
So far as the minerals are for any reason in a state of strain, this is 
very favorable forsolution (see pages 300, 301), and the process under such 
circumstances goes on at a comparatively rapid rate. 
The minerals under mass static conditions, at least within the zone of 
observation, are usually rearranged or recrystallized according to the first 
part of van’t Hofi’s law, with the liberation of heat, as, for instance, by 
hydration or carbonation. In so far as the minerals are buried to some 
depth, and consequently under considerable pressure, there is a tendency 
to change to minerals of a higher specific gravity. The depth at which 
the pressure is sufficient, without mass dynamic action, to produce de- 
hydration, and to substitute silicon dioxide for carbon dioxide, is uncer- 
tain, but that these reactions occur is certain; for no lower limit can be 
assigned to recrystallization under mass static conditions. 
That the recrystallization of great masses of sedimentary and igneous 
rocks may go far toward or quite to completion under mass static 
conditions is so well known that the fact need not here be emphasized. 
One of the best illustrative American localities is that of the Kewee- 
nawan series of the Lake Superior region. Asshown by Pumpelly + and 
Irving,{ the more porous lavas of this series have in many cases largely 
recrystallized. The less porous ones show extensive alterations. In vari- 
ous regions even great dense igneous masses have been profoundly affected 
or completely recrystallized throughout by metasomatic change. 
However, as subsequently seen, the rocks which have recrystallized 
under conditions of molecular dynamic action or mass static conditions 
are easily discriminated from those which have been recrystallized under 
mass dynamic conditions. 
* The voleanie rocks of South Mountain in Pennsylvania and Maryland, by G. H. Williams: Am. 
Journ. Sci., vol. xliv, 1892, pp. 482-496. 
The ancient voleanie rocks of South Mountain, Pennsylvania, by Florence Bascom: Bull. U.S. 
Geol. Survey, No. 136, 1896, p. 124. 
} Metasomatic development of the copper-bearing rocks of Lake Superior, by Raphael Pumpelly : 
Proe. Am. Acad. Arts and Sciences, vol. xili, 1878, pp. 253-309. 
{The copper-bearing rocks of Lake Superior, by R. D. Irving: Mon. U.S. Geol. Survey, no. v. 
1883, pp. 87-91. 
