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 Traic^ao 

 and the Lagoa de Sinimbii. 



Conclusions regarding the Consolidation op 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. 3, XXXIV., p. 163. 



