242 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



lime salts present into carbonate, we obtain a precipitate which varies both 

 in its crystalline form, in amount, and in time of formation. At 32 degrees 

 Fahrenheit the precipitate begins to form in about six hours as small but 

 distinct crystals of calcite, the quantity in twenty hours amounting only to 

 0.2 gramme from a litre of water. At a temperature of about 47 degrees 

 Fahrenheit a mixture of calcite and aragonite is precipitated; at 80 degrees 

 to 90 degrees Fahrenheit the quantity precipitated is about 0.6 gramme; the 

 precipitate begins to form in from a half to one hour, and it appears to con- 

 sist of minute crystals of aragonite. It thus seems evident that carbonate of 

 lime would be more easily and more rapidly secreted in the high temperatures 

 of the tropics by means of the effete products of the organism." 



MOTION OF THE WATER 



The adaptations of shallow-water corals to their respective habitats 

 are various. Although this subject has received more or less attention 

 since the days of Darwin, there is still some divergence of opinion. 

 Areas swept by strong, continuous currents are not favorable for the 

 growth of corals, as the free-swimming planulse have no opportunity to 

 affix themselves. Some species grow best where they are protected from 

 the ocean breakers; others thrive best in the region of the breakers or 

 just below the level of their pounding. For vigorous growth, the water 

 needs to be agitated and changed — that is, there must be circulation that 

 will continually supply fresh water. 



CHARACTER OF BOTTOM 



The bottom must be firm or must be overlain by masses of rock, so as 

 to supply suitable conditions for the attachment of settling coral larvae, 

 and the waters must be relatively free from silt, as deposits of such 

 material will bury the young corals and in considerable quantities will 

 smother older specimens. 



COMPOSITION OF THE OCEANIC SALTS 



There is no noticeable difference in the composition of the oceanic 

 salts in coral-reef regions from that in other regions of the ocean. The 

 following data are taken from F. W. Clarke's "The data of geochem- 

 istry," pages 94-95 : 



Mean of Seventy-seven Analyses of Ocean Water from many Localities, 

 collected by the Challenger Expedition 



W. Dittmar, analyst. Challenger Report, Physics and Chemistry, vol. 1, 1884, 

 p. 203. Salinity, 3.301 to 3.737 per cent. 



CI 55.292 



Br 188 



SO4 7.692 



COa 207 



