DIASTROPHISM AND. THE FORMATIVE PROCESSES 410 
mass to the side of it and belowit. The accommodation may take 
place by differences in the amount of wrinkling on the two sides, 
differences in the extent of elongation and schistosity, or differ- 
ences in some less clearly defined type of rock flow. It may be 
merely a zone in which, as one goes from the undeformed region 
into the crumpled mountain belt, folding rapidly becomes more 
pronounced and an increase in schistosity becomes marked. The 
dividing belts may be vaguely outlined or they may be more 
sharply defined. 
Because the wedge shape seemed to be in general harmony 
with certain recognized facts and principles, it was natural enough 
to suspect that it might prove to be a type of diastrophism of wide 
application. Wedge dynamics might prove to be characteristic 
of other mountain systems, and might be applied perhaps also to 
the elevation of plateaus, and those movements which control the 
rise of continental masses. A plateau-forming movement, if the 
outcome of lateral thrusting, would be assigned to a thick shell 
gently wrinkled. Very little shortening of a still deeper section 
would suffice to elevate a mass of continental dimensions. 
In ro10, following the publication of the Appalachian paper, an 
attempt was made to apply these principles to continental dias- 
trophism. Cross-sections of the globe were drawn with border 
planes dipping inward beneath the continents at 45°. Because 
of the curvature of the earth, each plane, in order to carry out 
the principle consistently, was drawn to cross the different radii 
of the globe at 45°. The result of such a treatment is shown in 
Figure r. Outlined thus, the continents appear as shallow units 
very subordinate to the oceanic segments. The latter are truly 
the master segments, which squeeze the continental wedges periodi- 
cally outward, as well as laterally, when the materials of the 
contracting globe become strained beyond their yielding point. 
This suggested extension of the wedge principle to the continents 
was not pushed farther at the time, for the reason that certain 
possible objections quickly came to mind, so that it seemed advis- 
able to allow the question to lie fallow for a while and await develop- 
ments. After a wait of ten years, during which time this principle 
was discussed with several successive classes of graduate students, 
