Nansen's Continental Oscillations — Spencer. 231 
must at any rate, become much steeper than that of the 
coast platform." Under such conditions, 'the force of the 
waves would be broken long before they reached the shore. 
There would be little opportunity for the waste formed by 
marine denudation, as well as the waste carried by rivers, 
to be washed away into the deeper waters" except by tidal 
and wind currents, (p. 105) which would heap up beaches 
that would further protect the cliffs from marine erosion. 
In the case of fjord-dissected coasts, the marine denuda- 
tion would be facilitated by the deposition of the waste 
in the deeper channels, so that the unbroken waves could 
reach the cliffs. However the last glaciers may have swept 
away previous accumulations of waste, thus re-opening the 
channels. So also atmosphere erosion is more effective on 
a deeply dissected coast than on a smooth one. The coast 
platform would be found in shallow water after the sub- 
mergence of the channeled peneplain. 
\\'hile continental shelves resemble coast platforms, 
they are more complicated and of greater extent ; as for 
instance extending from the Arctic basin to Patagonia, 
with their depth ranging mostly between 50 and 200 
metres. 
The four chief methods of production seem to be : that 
they are submerged coast platforms; submerged pene- 
plains : constructed by sea deposits ; and built up by glacial 
drift. Dr. Nansen concludes that the continental shelves 
of the world have been formed partly by coastal deposition 
of terrigenous waste, and partly by the conjoint action of 
sub-aerial erosion (i. e. submerged peneplains) and marine 
denudation ; and in seas favorable coral growths have been 
important. In regions of rapid coastal sedimentation, this 
method of formation has been primary; but it is not certain 
that favorable conditions obtained wherever broad banks 
occur, as those off Newfoundland and the shelf of the 
English channel. In such cases erosion has predominated 
in the formation. The Norwegian and Iceland shelves 
have been cut in solid rock at sea levels lower than now. 
"It can hardly be merely an accidental coincidence that 
the shelves have nevertheless levels which are nearly iden- 
tical with those of other continental shelves." of similar 
