136 CA. COTTON 
formed accumulated marginally to, rather than upon, one of the’ 
continental protuberances. 
The subject of marginal sedimentation is closely connected with 
considerations as to the form and origin of the continental shelf. 
While this is recognized by geologists and implied by many in their 
writings it is not usually explicitly stated. 
OPINIONS AS TO THE MODE OF FORMATION OF THE 
CONTINENTAL SHELF 
There isa very striking contrast normally present between the 
gentle slope of the continental shelf and the relatively steep 
descent, known as the continental slope, from the edge of the shelf 
to the depths of the ocean. In textbooks this is pointed out, but 
an explanation of it is generally avoided. 
Lake,’ however, has included a discussion of the problem. In 
Lake’s textbook and in a recent paper by Gardiner’ several 
hypotheses bearing on the subject are formulated. From both 
the reader receives the impression that, if a hypothesis of glacial 
deposition be put aside as of local application, there remain in the 
field to account for the continental shelf in low latitudes two rival 
hypotheses or groups of hypotheses behind each of which there is 
an equal weight of authority—namely, a hypothesis of erosion with 
or without subsidence of the eroded surface, and a hypothesis of 
accumulation according to which the shelf has grown owing to 
deposition of sediment. It is clear, however, that both these 
writers favor the hypothesis of accumulation and regard the shelf 
as for the most part a built feature. 
The acceptance of this view is the basis of many geological 
writings, such, for example, as an article by Chamberlin on “The 
Ulterior Basis of Time Divisions . . . . ,’’3 in which it is taken as 
axiomatic that the shelf is formed partly by cutting but mainly 
by deposition. The same point of view is implied by the use of 
such terms as ‘‘continental delta”? by Gulliver,’ signifying conti- 
=P. Lake, Physical Geography (Cambridge, 1915). 
2 J. Stanley Gardiner, “Submarine Slopes,” Geog. Jour., XLV (1915), 202-10. 
3T. C. Chamberlin, Jour. Geol., VI (1898), 449-62; also Editorial, pp. 424-26. 
4. P. Gulliver, ‘‘Shoreline Topography,” Proc. Amer. Acad. Arts and Sct., 
XXXIV (1890), 176. 
