104 K. A. DALY— METAMORPIIISM AND JTS PHASES 



crystalline schists, is truly inexplicable by pure dynamic nietaniorphisni. 

 Tlie parallelism is found, whether or not the dips are persistently low or 

 high or persistently changing across-comitry. Since new metamorphic 

 minerals seem to be regularly elongated at right angles to the metamor- 

 phosing stress, the schistosity produced by intense orogcnic movements 

 (tangential force) will be parallel to bedding only in comparatively rare 

 and narrow belts. Prevailing parallelism in a terrane of variable dip is 

 therefore a good indication that dynamic metamorphism has not con- 

 trolled tlie recrystallization. Elementary as it is, this principle has been 

 wonderfully neglected in most of the recent discussions of regional meta- 

 morphism. 



A fourth argument, connected with the last, has independent power. In 

 the Shuswap terrane, in the Precambrian of eastern North America, and 

 in many other schist areas the crystallinity or degree of metamorphism 

 is, to a large extent, not directly related to the amount of crustal deforma- 

 tion. ]\Iany vertically dipping schists are practically identical in habit, 

 including size of grain, with neighboring, little- deformed schists of the 

 same chemical composition. For this fact the assumption of load meta- 

 morphism, active before the mountain-building, offers the only explana- 

 tion yet proposed. 



Of course, a rock series already recrystallized by load metamorphism 

 may be affected by later alterations of dynamic origin. Beautiful ex- 

 amples are visible among the Shuswap rocks (Daly, 1915, plate 21). 

 Such superposition of metamorphisms may thus obscure the whole prob- 

 lem of origins. In fact, its solution has doubtless been retarded because 

 special students of metamorphism have so largely worked in fields where 

 schists and gneisses happen to have been much dislocated since the re- 

 crystallization of those rocks. Most w^orkers have not sufficiently can- 

 vassed the question as to what w^as the condition of each rock formation 

 before upturning. The proof of recrystallization in zones of intense 

 dynamic stress has too easily led to generalizations as to the genesis of 

 the rest, often the greater part, of the same terrane, where crustal defor- 

 mation has been less or w^here its causal connection with the visible meta- 

 morphism can not be demonstrated. 



Finally, the fully significance of load metamorphism is not understood 

 until its relation to the doctrine of uniformitarianism has been made out. 

 Koenigsberger (1910, page 651) and Pies and Watson (1915, page 203) 

 deny that deep burial has caused regional metamorphism, on the ground 

 that many Paleozoic and younger strata, though once covered by thou-, 

 sands of meters of rock, have not been changed to crystalline schists. 

 The present writer (1912, page 479) has observed a nearly complete ab- 



