22 N. M. FENNEMAN 
Relation of the phenomena above to agitation on the bottom.— 
It is to be inferred from what precedes that symmetrical wave 
form indicates freedom from interference at the bottom, that 
friction below is great in proportion as crowding, steepening, 
and asymmetrical form above are prominent, and that where an 
off-shore breaker line is seen it indicates a maximum of bottom 
interference. It is understood in all cases that the surface effect 
will lag a little behind the cause below, and therefore appear a 
little to shoreward. 
PROFILES RESULTING FROM FORCES DISCUSSED ABOVE. 
In the actual operation of the forces discussed above, the 
resulting action on a sloping bottom may be outward at all 
places, or inward at all places, or outward over one part and 
inward over another. Forces in either direction may be gradu- 
ualiy augmented or diminished. The different forces are capable 
of different combinations. Each set of conditions will lead to 
certain features of profile. If there be no change of condition, 
a permanent profile of equilibrium may be reached. The con- 
stant supply of load constitutes an ever shifting condition. 
Equilibrium as commonly realized depends on the uniformity of 
this supply. 
Factors in profile-making.—The agencies which shape the 
marginal bottom may be treated in three groups, (1) oscil- 
latory wave action and undertow, carrying material from shore ; 
(2) on-shore currents and translatory wave action, carrying the 
material toward the shore; (3) currents alongshore. The tend- 
ency of the first group is to steepen the slope from the water’s 
edge to the line at which its erosive power ceases, and deposi- 
tion begins and to reduce the slope beyond that line. There is 
also for the second group a line of maximum power on the 
bottom, within which their effect is to steepen the profile by 
accumulation at the water’s edge, and beyond which the slope 
is reduced by cutting down. Currents alongshore will be intro- 
duced later. 
Conflict between on-shore and off-shore action—The first two 
