Geology, S'^'S 



barrier pools and on the barrier flats (20), and on the exposed 

 reef (16). Of these only 5 are common to two and 1 to three of 

 the habitats. We therefore see here that the percentage method 

 of correlating an assemblage of fossil forms can have no value m 

 determining the ages of the various ancient faunas. 



On pages 238-332 are presented the ''Conditions under which 

 the West Indian, Central American, and Floridian coral reefs 

 have formed, and their bearing on theories of coral-reef forma- 

 tion.'' Some of the author's conclusions are striking, as, for 

 instance, that the great majority of offshore reefs, recent and 

 Cenozoic, "are superposed on antecedent flattish basements or 

 platforms" and that they have started to grow upon them "fol- 

 lowing considerable submergence . . . almost certainly due to 

 differential crustal movement." "None of the American plat- 

 forms were formed by infilling [of living corals] behind a bar- 

 rier." The inner flat-bottom shallow seas of atolls are not due 

 to submarine sokition by sea water; they are antecedent bot- 

 toms on which constructional rings of organic material have 

 grown upward. 



"The Darwin-Dana hypothesis, in my opinion, is correct as 

 regards the formation of off'shore reefs during and after submer- 

 gence ; but as regards the formation of a prism of reef material, 

 the upper surface of which forms a flat behind the barrier, their 

 theory is wrong for every area on which we have definite informa- 

 tion. . . . 



' ' Semper, Alexander Agassiz, and others, who have maintained 

 that barrier coral reefs have formed in areas of uplift, are correct, 

 if the sum total of the movements since some date back in Ter- 

 tiary time be considered, and their observations and deductions 

 are valuable in that they emphasize these facts ; but they are in 

 error in that they failed to take into account that in many areas 

 there is incontrovertible evidence sho^dng submergence of the 

 basements of the now-living reefs. . . . 



"Sir John Murray invented a very stimulating hypothesis, 

 and correctly emphasized the necessity of taking submarine plan- 

 ation into account in studies of the basements of coral reefs. 



"Daly did not originate the Glacial-control theory of coral 

 reefs, but he is its principal exponent. The following ascer- 

 tained relations of living offshore coral reefs conform to the 

 demands of this hypothesis: {a) They are superposed on ante- 

 cedent basement flats; (b) the amount of recent submergence, 

 between 30 and slightly more than 20 fathoms, without deducting 

 the amount of Recent up-building of the sea bottom, which prob- 

 ably is as much as a few fathoms, is of the order of magnitude 

 expected from deglaciation ; (c) the rate of growth of corals is 

 known to be of such an order of magnitude as to account for the 

 thickness of any known living coral reef by the growth of coral- 

 reef organism since the disappearance of the last great continental 

 glaciers." (326-328). c. s. 



7. Studies in Minor Folds; by Charles E. Decker. Pp. 



