306 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. | 
quartz in the quartz-porphyries described by Futterer* (plate 19, figure 1) 
and in many other rocks in which the feldspars have either been gran- 
ulated or little affected. 
At this time I shall make no attempt to compare the various minerals 
with one another with reference to ease of recrystallization. There are 
all gradations, from calcite, which can be easily recrystallized in the 
laboratory by the passage of water through finely powdered material 
under very moderate pressure, to the more refractory minerals, such as 
feldspar. 
Since some minerals when strained recrystallize much more readily 
than other minerals, it follows that a formation composed chiefly of one 
class of minerals may be largely recrystallized, while an adjacent set of 
rocks composed of another set of minerals may be only partially re- 
crystallized. One formation might thus show complete granulation or 
other important strains, while the recrystallization of the adjacent for- 
mation, because of the greater mobility of its mineral particles, might 
nearly keep pace with the deformation. One rock might show the textures 
and structures of the crystalline schists with more or less residual strain 
effects, while an interlaminated rock might so readily recrystallize as to 
take on a granolitic texture after movement had ceased. As an illustra- 
tion of this are the closely associated gneisses and marbles of the Adiron- 
dacks and of the Hastings series of Canada. Many of the gneisses show 
marked strains in various localities, while interstratified with these are 
coarsely crystalline marbles, showing no other strains than those of poly- 
synthetic twinning and similar phenomena, which may have been de- 
veloped by the slight stresses to which the material was subjected in 
section cutting in the laboratory. 
No better example is known to me of the influence of the character of 
the material upon the gradations and relations between granulation and 
recrystallization than the Algonkian rocks of the Black Hills,t described 
in volume I of this Bulletin. There conglomerates, quartzites, mica- 
slates, mica-schists, and mica-gneisses occur in intimate relations to one 
another. Nearly every phase of deformation, from that of granulation 
as a dominant process to that of recrystallization, is represented. : 
Water content.—Absence of water is favorable to granulation ; presence 
of water is favorable to recrystallization. Ifa series be so dense or is of 
such an origin as to contain comparatively little water, even if other 
conditions be favorable, deformation by granulation rather than by re- 
crystallization may occur. Another series in every other respect under 
*Adams, op. cit., pp. 47, 48. 
+ The pre-Cambrian of the Black Hills, by C. R. Van Hise: Bull. Geol. Soc, Am., vol. i, 1891, pp. 
214-229. 
