AGENTS AT WORK IN THE OCEAN 229 
maintains a nearly vertical position (Fig. 129). But 
weathering, also operates to wear it back, and therefore 
it may not be absolutely vertical. If the coast rock is 
soft, the wave-formed cliff will be a sloping one. 
The methods of wave action vary widely with the 
conditions. In case the products of this coast mill can 
be removed, cliffs are cut and sometimes beaches built 
at their base, representing the accumulated materials 
which have not — 
yet been carried 
away (Fig. 129). 
These sea cliffs 
may be very ir- 
regular, for the 
waves will cut 
into some rocks 
morereadily than Fig, 128. 
others; and thus 
headlands will be made to jut beyond little indentations 
(Fig. 150), which mark the site of the more easily 
Sea cave in cliff at Mt. Desert Island, Maine. 
destructible rocks. 
It is sometimes stated that harbors, estuaries, and 
bays, even those as large as the Chesapeake, have been 
cut out of the land by the action of the ocean; but 
this 1s an error. Such large irregularities have been 
caused by a sinking of the land, which has allowed 
the sea to enter river valleys and transform them 
