126 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
“When the land is sinking . . . the drowned river valleys make the 
coast irregular and complicated.” 
Another characteristic of recently sunk coasts is that fringing islands 
usually abound along them. Immediately following a depression sedi- 
ments brought down by the streams and washed by the waves from the 
promontories and fringing islands silt up the bays and lower stream | 
channels, and only such channels are left as the tides are able by their | 
scouring action to keep open. At first the tide flows further inland and 
there are many harbors on the new coast, but in the course of time the 
silting up of the estuaries crowds the tide back to the open coast-line. 
If the depression goes on more rapidly than silting, the tides extend 
further and further inland ; but if silting and the constructive work of 
the sea are more rapid the tides are kept back. Depression brings 
within the reach of the waves a new surface and adds greatly to their 
cutting power, and consequently large quantities of silts are produced. 
If the prevailing winds blow on shore, as they do on the Brazilian coast 
all the year round, the heavier silts cut from the headlands are thrown 
back into the bays rapidly, the beaches of sand extend seawards, the 
closing of the mouths of streams and estuaries are hastened, and there 
is a general tendency to form a straight shore. 
The marshes built out in the depressions are soon covered with man- | 
groves, and the streams in some cases wander behind the beaches for | 
some distance before breaking through them to enter the sea. We thus | 
eventually have the coast marked by a succession of tide marshes and | 
lakes, with long straight beaches in front of them, and with here and | 
there a headland coming down to the sea. 
If, however, the silts cut from the shore-line are swept away by the 
currents, either along the shores or seawards, the coast soon exhibits a | 
continuous bluff and the sea encroaches upon the land until an equilib- 
1 The question might be raised as to whether the materials cut from a conti- 
nental shoulder would be thrown on shore or carried seaward by the undertow. I 
do not think a fixed rule for this can be given. In some cases one thing happens, 
and in others the other. In some localities the fine black silts containing marine 
organisms are constantly thrown back into the estuaries, in other cases the coast is 
kept clear of fine silts by the undertow. 
(The estuaries of the Severn, etc. Ву W. J. Sollas. Quar. Journ. Geol. Soc., 
1883, XXXIX., p. 619; discussion by Mr. Whitaker, p. 625-626.) 
Postscriptum.— In a late article Mr. Fenneman points out that waves of transla- 
tion tend to carry the materials on the shores upon which the waves break, while 
waves of oscillation move materials in the direction opposite to that in which the 
waves move, (Journ. Geol., Jan.-Feb., 1902, X., p. 13-14.) 
