BRANNER: THE STONE REEFS OF BRAZIL. 105 
Inasmuch as the beaches of which the reefs have been made have the 
appearance of being accumulations or accretions, we may set aside the 
probability of their having been formed by the elevation of a smooth sea 
bottom and deal with the methods by which straight beaches are pro- 
duced from crooked ones. 
They may be considered as originating in two ways, or by a single 
structural process, operating under two different conditions. These con- 
ditions may produce : — 
First, shore beaches, — the accumulations along the margin between 
the mainland and the main body of water. 
Second, of-shore beaches, or the beaches developed as spits, bars, or 
barrier beaches lying parallel with the main coast-line. 
The shore beach. — The form of a shore-line is determined (1) by wave 
action, (2) by the resistance of the shore rocks to marine encroachment, 
and (3) by the direction of inshore currents. Оп a coast having alter- 
nate bays or estuaries and headlands, we inevitably have alternate cur- 
rents and eddies next to the shore. The waves and currents attack the 
headlands and throw the coarse materials cut from them into the more 
quiet waters of the bays, where they sink to the bottom. If, however, 
the prevailing winds drive the waves squarely against the shores, tho silts 
are thrown back against the inner margins of the bays, and the beaches 
are built outwards by a continuous and approximately uniform process 
of accretion. The tendency along such shores is, therefore, for the 
beach gradually to become straight by the cutting down of the headlands 
and the outbuilding of the concave beaches. The early beaches must, 
therefore, have been crooked, or more so, at least, than the later ones. 
The temporary shiftings of the currents, either of the streams or of the 
sea, have probably played an important part in determining the forms and 
locations of the beaches and of the stone reefs. 
It is evident, however, that the straight beaches are comparatively 
mature ones, for it is only after the agencies mentioned have been in 
Operation for a long time that the broken line of the early history of the 
Shore becomes a straight one.! 
The off-shore beach. — Offshore beaches might be divided into those 
originating as spits and those built up from the bottom as bars not 
connected at the surface with the land. No sharp line can be drawn 
between them, however. If the near-shore currents or the prevailing 
1 Lapparent says, “the work of thesea on flat coasts is essentially constructive.” 
(Traité de géologie, 2те ed. 171.) This statement, however, might be turned 
about and be equally true; that is, a newly constructed sea-coast is essentially flat. 
