REVIEWS ■ 749 



I. Ihey are of sand consolidated to a hard — in places almost quartzitic — 

 sandstone. 



II. They stand about flush with the water at high tide, while at low tide they 

 are left exposed like long, low, flat-topped walls, with a width of from nve meters 

 to one hundred and fifty meters, and a length of from a few paces to several 

 kilometers. 



III. They accompany the shore-line with many and great interruptions 

 from north of Ceara to Port Seguro, a distance of two thousand kilometers. 



IV. AVith unimportant exceptions, the reefs do not occur along the Brazihan 

 coast beyond these limits. 



V. They usually stand across the mouths of streams and estuaries,, forming 

 perfect natural breakwaters for the small harbors behind them. Sometimes 

 they follow the shore, either on the beach or at a short distance from it. 



VI. They are all nearly straight. When crooked, their curves are gentle. 



VII. The structure and position of the reefs and the animal remains they 

 contain show that they have been made by the lithification of beach sands in 

 place. 



VIII. When stone and coral reefs occur together, the stone reefs are inside 

 or landward of the coral reefs. It is possible, however, that there may be buried 

 coral reefs in some cases to the landward of some of the stone reefs. 



IX. The coral reefs are now growing over and upon the stone reefs in some 

 places, while at other places there are stone reefs overlying dead coral reefs. 



X. In general appearance, elevation, and position the sandstone reefs bear 

 a striking resemblance to the coral reefs. 



The characteristics of these reefs are set forth by careful detailed descrip- 

 tions, unusually well illustrated by excellent sketches, cross-sections, 

 outline maps, coast charts, and photographic plates (104 figures, 99 plates). 

 The treatment also includes the discussion of several collateral themes, 

 among wliich are the coast changes, concerning which the following con- 

 clusions are drawn: 



1. There is no evidence of a perceptible change of level of the coast since 

 the discovery of Brazil. 



2. Changes have taken place in the form of the coast-line, and in the adjacent 

 streams, bays, and estuaries in historic times, but they are all accounted for by 

 the ordinary processes now in operation. 



3. The stone reefs are not metamorphosed or folded, and they do not rise 

 above tide-level, except in a few instances, where blocks have been tilted by the 

 undermining done by the waves. 



4. The coast lakes have been formed by the damming in of estuaries, by the 

 sands blown along the coast, and by the throwing back into the estuaries of detritus 

 cut by waves from adjoining headlands or brought down by streams from the 

 land. 



