MASS DYNAMIC ACTION. 301 
to part with their molecules than the minerals not so conditioned. Thus, 
from all mineral particles which are under one or all of these conditions, 
particles will be filed off or solution will be constantly taking place. 
Simultaneous with this, from the solution there will be deposition of 
material in more compact molecules than those dissolved at the places 
where the pressure on the mineral particles is less than the average. 
Two of the best minerals to illustrate the process are quartz and mica. 
The first recrystallizes somewhat readily, and the second develops on an 
extensive scale in the crystalline schists. That quartz occurs abundantly 
in flat individuals in the crystalline schists is well known. Moreover, 
it is known in many cases that the flat individuals are largely the equiv- 
alent of individual crystals which have had a nearly spherical form. As 
illustrations of flat grains of this mineral are the quartzes of the quartz- 
porphyries described: by Futterer* (plate 19, figure 1) and mica-schists 
from the Black Hills+ (plate 19, figure 2), which I have described. 
The many flat particles have exactly the appearance they would have 
had if the material could have been pressed out and had recrystallized 
anew as a single individual and subsequently had been somewhat 
strained. In some cases the flat individuals have a somewhat curved 
form (plate 19. figure 1; also see page 323). The explanation suggested 
by Adams for the deformation of the quartz of the leaf gneisses of the 
Original Laurentian district is movement along gliding planes, as advo- 
cated by Mtigge in reference to ice crystals. However, this explanation 
seems inadequate to explain the phenomenon above described, for two 
reasons: First, the greater dimensions of the flat quartz individuals al- 
ways correspond to the schistosity, and are wholly independent of the 
orientation of the original particles, and therefore independent of their 
gliding or other definite planes. If gliding had taken place, this must 
have occurred along definite crystal planes. Second, as shown (page 
3035), in many cases during recrystallization the material of a multitude 
of particles is built into a single particle. Hence it seems perfectly clear 
that gliding along any set of definite planes will not explain the facts. 
The phenomena are believed to be.due to solution and deposition, or re- 
crystallization, as already explained. The particles of the quartz not 
fortunately oriented at places under great stress—that is, upon the ex- 
posed parts of the grains—are taken into solution and transported to the 
borders of the fortunately oriented individuals, where less stressed, and 
redeposited ; or, the material dissolved from the more exposed part of a 
erain may be deposited on another part of the same grain. Thus the 
*Die ‘“Ganggranite”? von Grossachsen, und die Quartzporphyre von Thal im Thuringer Wald, 
by Karl Futterer: Heidelberg, 1890, pp. 27-47. 
+The pre-Cambrian rocks of the Black Hills, by C. R. Van Hise: Bull. Geol. Soe. Am., vol. i 
1890, pp. 222-226, 244. 
5) 
XLV—Butt. Geo. Soc. Am., Vou. 9, 1897 
