BRANNER: THE STONE REEFS OF BRAZIL. 125 



ancient indentations of this coast have been obliterated by time and 

 the sea. 



Comparative effects of elevation and depression. — The relations of 

 the reefs to the shores and to the coast topography makes it necessary 

 to deal with the topographic forms of the reefs and to understand by 

 what processes and in what order they originated. 



The general effects of elevation on any coast will be considered first, 

 and afterwards the effects of depression, and then by comparing the lit- 

 toral forms thus produced with those of the Brazilian coast the writer 

 will try to determine by which of these movements its present features 

 have been produced. 



Effects of elevation. — If any coast were considerably and abruptly 

 elevated the old beach-line would form a terrace, the old undercut shores 

 would be mai'ked by an incised line produced by the former work of the 

 waves, the coral reefs of the region would be exposed, the polyps killed, 

 and the remains of marine animals, especially the Mollusca, would be left 

 strewn across the newly raised land. The streams would have their cur- 

 rents increased about their former mouths and would immediately begin 

 to cut into their rock bottoms and to make deep, steep-sided channels. 

 If there were partly enclosed bays or lakes along the former shores, their 

 outlets would cut deep channels back into the lakes and they would be 

 drained at once. Inasmuch as the irregularities of the land, on account 

 of subaerial erosion, are more marked than those of the sea-bottom, a 

 depression would, as a rule, yield a more indented coast-line, while an 

 elevation would yield a coast with but few harbors. 



An elevation of three or four metres on this Brazilian coast would pro- 

 duce a peculiar effect upon the stone reefs ; the waves would undermine 

 the reefs, for as has elsewhere been shown, they ai'e hardened only to 

 this depth, and they would break into angular blocks and strew the 

 newly made beach with their remains. 



Effects of depression. — If a considerable depression took place on a 

 sea coast, the valleys near the coast would be flooded and would become 

 bays, narrow estuaries, or fjords, accoi'ding to the shapes of the valleys. 

 In general, the coast-line would have the dentritic form suggested by 

 the coast of Maine more or less marked, according to the relief of the 

 region before the depression took place. 



This is so universally true that Dr. James Geikie in his recent work 

 upon " Earth Sculpture " states (p. 328) that, " All highly indented 

 coast lines are evidence that the land is sinking or has recently sunk." 

 Lord Avebury, in his ''Scenery of England," observes (p. 125) that. 



