156 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
satch range. This may, as usual, be best demonstrated by consideration 
of the progress of wave work in an ideal case. 
If the surface of a sea or lake should rise on a ravined mountain 
front, so as to gain an irregular shore line, aBcp, Figure 12, the promon- 
tories might in time be cut back to the straight shore line DFH, over 
which the spurs would then terminate in triangular cliff-facets, DKF, FLH. 
But in such a case, the valleys should not remain narrow-mouthed during 
the progress of the wave work, but should widen somewhat and allow the 
streams to develop flood plains on which they could wander a little ; 
and after the lake waters had disappeared, the facets should look out 
Figure 12. 
Diagram of spurs cut by waves: ABCD, initial shore-line at time of submergence; DKF, 
cliff facet cut back in spur DEF; FGH, spur platform fronting its cliff facet FLH, 
after withdrawal of lake waters. ry 
upon triangular rock platforms, raH, systematically related in form and 
area to the facets. As a matter of fact the triangular rock-platforms and 
the widened valley mouths are wanting in every case that came under 
my notice. It cannot be supposed that the mountain front was cut back 
by waves at so low a level that the wave-cut platform is now concealed 
by mountain waste ; for in that case the narrow ravines should also have 
been cut down to the same low level, instead of opening, as they so often 
do, rock-floored on the mountain flank, and allowing the streams to con- 
tinue their descent on gravel fans that rise at the apex distinctly above 
the intermont plain. One of the best localities for the illustration of 
