PETROLOGICAL ABSTRACTS AND REVIEWS 275 
CONTROLLING FACTORS OF EACH ZONE 
Gecreeracre) oereeeeg) | PgCrRS | Veena, | aptecomanan Ere 
Upper zone. .| Moderate — Slight Great Mechanical 
Middle zone.| Greater — (—) | Greater Very Chemical (Vol. law, 
great Riecke prin.) 
Deep zone...| Very great —=- «| Very great. | ess Chemical (show re- 
crystallization 
with retention of 
form) 
TABLE OF ROCKS OF EACH ZONE 
Upper zone. Quartz phyllite, sericite phyllite, lime phyllite, chloritoid schist, 
chlorite schist, talc schist, serpentine, epidote fels, and topfstein. 
Middle zone. Muscovite schist, muscovite-biotite schist, biotite schist, garnet- 
staurolite-actinolite schist, nephrite-glaucophane schist, mica 
gneiss, hornblende gneiss, garnet gneiss, epidote gneiss, marble, 
quartzite. 
Deep zone. _Biotite gneiss, pyroxene gneiss, stillimanite-cordierite-garnet 
gneiss, granulite, garnet-mica schist, garnet fels, eclogite, 
jadeite, augite fels, marble, quartzite. 
II. The various conceptions which assign the origin of crystalline 
schists to the agency of eruptive rocks can be grouped as: 
1. Those which regard gneisses as primary unaltered eruptive rocks. 
2. Those which ascribe the crystalline schists to the result of the 
metamorphic action of igneous rocks on sediments. 
Crystallization of magmas under differential pressure or piezo- 
crystallization (Weinschenk) and the deformation of igneous rocks while 
still charged with hot juvenile waters (Becke) have been suggested as 
processes which might explain the first. 
Direct contact metamorphism, injections of the intrusive, mainly 
along parallel zones into the intruded rock, the action of mineralizers, 
and the absorption of the intruded by the intrusive rocks have been 
advanced by various writers as processes by which gneisses and schists 
have developed through the agency of igneous rocks. Michel Levy has 
pointed out that the alteration of sediments into schists and gneisses 
adjacent to contacts is not confined to recrystallization, but that there 
is a zone of impregnation which becomes regional with depth. Slow 
recrystallization has little effect on texture as contrasted with forcible 
injection of the intrusive and partial absorption of the older rock. 
Occasionally, the contact between a slate and granite is marked 
by series of parallel injections of the granite into the slate, while masses 
