DEPOSITION ON CONTINENTAL SHELF AND SLOPE 145 
-“mud-line” of Murray and Renard, which, according to Murray, 
is situated at a depth of about 100 fathoms.’ On the slope below 
this depth the finest particles of sediment “‘come permanently to 
rest on the bottom.’”’ Beyond the mud-line is the steeper foreset 
slope on which even the finest waste can come permanently to rest; 
but the foreset slope is much less steep and the transition to it from 
the subaqueous plain much more gradual than in the case of the. 
small deltas of coarse material in lakes. For one thing water- 
logged mud will not remain at rest on any but very gentle slopes, 
and, as Barrell points out, “‘where, as in the case of large rivers, the 
detritus is mostly fine in texture, the foreset beds are built largely 
by material settling from suspension.’”’ The foreset beds, in which 
sediment swept outward along the bottom is mixed with what has 
settled from suspension, grade into the bottom-set beds or pelagic 
deposits built entirely of material settling from suspension. 
In the case of portions of the continental shelf remote from the 
mouths of large rivers the mode of accumulation must be essentially 
the same as in deltas; but there will generally be present in the 
waste supplied from the land a much smaller proportion of the fine 
mud particles resulting from subaérial weathering. No doubt 
much of the material broken by wave attack on the shore line and 
supplied by smaller rivers becomes very finely comminuted in its long 
passage across the shelf; but the absence of a large body of mud 
sufficiently fine to be carried far seaward in suspension is reflected 
in a sharper transition from the continental shelf to the continental 
slope, and in a steeper inclination of the latter than is found in delta 
fronts. Thus the structure of the continental shelf may be regarded 
as presenting generally a closer resemblance to that of the sub- 
aqueous portions of small lake deltas than is shown by the corre- 
sponding portions of the deltas of great rivers. 
The materials of which the shelf is being built forward are 
known from samples taken by oceanographers from the last layer 
added. ‘These deposits on the continental slope fall into the 
“terrigenous’’ division of ‘‘deep-sea deposits, beyond 100 fathoms”’ 
in Murray and Renard’s classification of marine deposits,? and the 
t Sir John Murray, The Ocean (Home University Library), (London), p. 202. 
2*‘Tyeep-Sea Deposits,” Report of the Scientific Results of the Exploring Voyage 
of H.M.S. “Challenger,” 1873-76.(London, 1891); Murray, The Ocean, p. 201. 
