DEPOSITION ON CONTINENTAL SHELF AND SLOPE 143 
cut remains essentially stationary in level, and during which an 
enormous quantity of waste is carried to the sea. Such waste will 
be deposited seaward as a continental shelf of unusually great 
breadth, and this, when submergence of the peneplain takes place, 
will subside also. Since, presumably, the edge of the shelf before 
subsidence will be situated at or just within the 1oo-fathom line, 
after subsidence has taken place, when the width of the plain will 
have been added to that of the former shelf, the composite shelf 
so formed will extend into water much deeper than roo fathoms. 
Upon such a shelf a thick layer of sediment would require to be 
deposited to reduce the depth at its edge to 100 fathoms; and 
so it appears evident that submergence of a peneplain without 
the subsequent co-operation of wave action on an extensive 
scale is not competent to produce a continental shelf of typical 
form. 
The profiles of the shelf in the diagrams given by Gardiner to 
illustrate the ‘‘formation of the continental shelf by the submer- 
gence of an abrasion platform” and “of a land plain” are quite 
unlike those found in nature. This is perhaps intentional, as that 
author does not appear to favor either hypothesis. Such initial 
profiles would be very readily modified by wave and current action, 
according to the principles deduced by Fenneman. 
Two stages of such modification are shown in Fig. 2b as an 
addition to Gardiner’s diagram of ‘‘submergence of a land plain.” 
The deposit added in an early stage of the modification is coarsely 
stippled, and that in a later stage lightly stippled. 
The hypothesis that the continental shelf is formed as a result of 
deposition.—The conditions of delta-formation by streams bearing 
a load of coarse waste into lakes are now well understood chiefly 
owing to the work of Gilbert, and an extension of the principles 
established by Gilbert to cover the case of rivers supplying large 
quantities of finer waste to the ocean has more recently been made 
by Barrell.?, It is but a step from the consideration of the 
1G. K. Gilbert, ““The Topographic Features of Lake Shores,” U.S. Geol. Surv., 
5th Ann. Rept., 1885, pp. 69-123. 
2J. Barrell, ‘Criteria for the Recognition of Ancient Delta Deposits,’’ Bull. 
Geol. Soc. Am., XXIII (1912), 377-446. 
