BRANNER: THE STONE REEFS OF BRAZIL. 195 
We are, therefore, obliged to conclude that the process of hardening is 
not perfectly continuous. This lack of continuity is not a time break, 
properly speaking, but simply a break due to local physical and chemical 
conditions. 
That the beds of sand harden in some places and not in others is a 
well-known fact, though just why it happens so is not always clear. 
Nelson long ago called attention to the difference in the hardening of 
the calcareous sands of Bermuda,’ and Dall notes the local hardening 
of the “ coquina ” in Florida.? 
It seems probable at least that the conditions of lithification are nicely 
balanced, and that they are readily and frequently disturbed. 
Some of these disturbances are due to geographic causes. When a 
stream enters the sea, there is a tendency for it to be crowded to one side 
by marine currents, especially during the low stages of the river water, 
but during freshets the river often breaks through the barriers heaped 
across its mouth by the sea, and establishes a new channel which it may 
or may not be able to keep open. In any case, there is a tendency for 
the stream behind the barrier to shift its channel, especially in the early 
part of its history, and this shifts the site of the active consolidation of 
beach sands. In the early development of the coast, the new beaches 
formed to seaward of the older ones, and this process continued until the 
cutting of the shores nearly ceased. Some of these newer beaches were 
hardened, but many of them were not, according to the relation of the 
beach to fresh-water bodies behind them. 
There is, therefore, no more reason for expecting a continuous process 
of hardening than for expecting all parts of a given bed to harden alike. 
The hardening is probably now in process in favorable localities. I have 
no doubt but that it is going on, for example, in the vicinity of Traigäo 
and the Lagóa de Sinimbu. 
CONOLUSIONS REGARDING THE CONSOLIDATION OF THE REEFS. 
Stone reefs are formed where there are streams or lakes of fresh water 
‚ entirely or partially restrained by the beach sands. The new reefs may 
be formed either in front of the old ones, or in the embayment and 
estuary behind the older ones. For similar reasons, stone reefs may 
form behind or landward of the coral reefs, This can only happen, 
1 Richard J. Nelson. On the geology of the Bermudas. Trans. Geol. Soc., 
London, ser. 2, V., p. 123. London, 1840. 
2 Amer. Journ. Sci., ser. 8, ХХХТУ., p, 168. 
