184 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



on the east shore of a continent than on the west shore,-^ and as Murray 

 points out, this favors the growth of corals along the eastern shores of 

 the continents. It must also favor the yielding up of carbon dioxide. 

 The conclusion seems warranted from these facts that the warming of 

 the sea-water of the South Atlantic equatorial current that sets against 

 the northeast coast of Brazil is capable of supplying all the carbon 

 dioxide necessary for the hardening of the stone reefs. 



Is tJie process universal? — But if the hardening of these beaches is 

 produced by the sea-water alone, why is it that the process is not a uni- 

 versal one, at least in the tropics 1 



From what has gone before, it might appear that it was simply a mat- 

 ter of carbon dioxide, eitlier of volcanic origin or derived from cold sea- 

 waters by warming them, in which case we might expect such beaches 

 in almost any part of the world. 



Now the relations of ocean currents and temperatures to carbonic acid 

 are not new, but must have existed for a long time. If the sands of 

 tropical shores have been consolidated by the aid of carbonic acid brought 

 in by ocean currents, this process of consolidation must have been going 

 on ever since the present currents were established, and it must be 

 going on to-day. Confining ourselves to the Brazilian coast, we should 

 expect to find, therefore, not a single or double line of stone reefs, but a 

 continuous series of hardened beaches overlapping eacli other, wherever 

 the coast line has been extended seaward by accx'etion, or exposed wher- 

 ever the ocean tends to encroach upon the land. As a matter of fact, 

 this is not the case in Brazil. 



Dr. Dall says ^ that in Florida " Coquina rock, frequently composed 

 more of sand grains than of shell, ... is doubtless being formed at 

 many points along the Gulf shore, though in small quantities at each 

 plitce, and not at all in the lagoons and harbors." He mentions a recent 

 rock that contains land and marine shells, in some places soft and in 

 other places (without fossils) ringing under the hammer. "What cements 

 this rock he does not state. Another is said to be hardened by iron 

 brought out in spring waters ; still another is hardened by lime coating 

 the sand grains. {Loc. cit., p. 164.) 



In order to ascertain whether recently consolidated beaches were 

 known about the British Isles, I have corresponded with Mr. W. Whita- 

 ker, lately President of the Geological Society of London, and some 



1 Murray and Irvine. Nature. June 12, 1890. XLIL, p. 163. 

 - W. H. Dall, Notes on the geology of Florida. Amer. Journ. Sci., 3d ser., 

 XXXIV., p. 163. 



