236 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



(a) There should be evidence of geologically Recent submergence of 

 most of the shore lines of the earth; (b) the average amount of the 

 submergence should be equal to the amount of lowering of the ocean 

 level during Pleistocene glaciation: (c) the position of the shore 

 line during Pleistocene glaciation should be indicated by scarps 

 separating flats, and the amount of submergence indicated by their 

 present position below sea level should agree with the amount of the 

 raising of ocean level due to deglaciation ; (d) the rate of growth, 

 corals should be such that since the disappearance of the continental 

 ice sheets coral reefs could grow to a thickness equal to the amount sea 

 level was raised as a result of deglaciation; (e) living barrier coral 

 reefs and atoll reefs should be superposed on antecedent basement 

 flats or platforms. It should here be stated that the fact that there 

 has been local differential crustal movements does not at all in- 

 validate the importance of the Glacial Control theory in its applica- 

 tion to the explanation of modem coral reef development. 



In the foregoing discussion it has been shown that within coral- 

 reef regions there has been geologically Recent submergence. The 

 shore lines of the earth can not be reviewed in this place, but it may 

 be said that the available evidence indicates that the sea has recently, 

 geologically speaking, overflowed the seaward margins of the land. 

 According to estimates by W. J. Humphreys 1 and by Daly the maxi- 

 mum amount of the lowering of sea level because of the abstraction of 

 water from the ocean to form the continental ice sheets was of the 

 order of magnitude of 67 meters (about 36 fathoms) . Daly has made 

 elaborate compilations of the depths of lagoons, lagoon channels, 

 and drowned valleys, in the coral reef areas of the Pacific and 

 Indian Oceans; and the lowering of sea level, between 55 and slightty 

 more than 37 meters, indicated by the compilations agrees with the 

 computations about as closely as should be expected. I obtained 

 similar results in the West Indies. The accompanying text figure 

 16 indicated a raising of sea level in excess of 37 meters (20 fathoms), 

 on the basis of interpreting the steeper slope at a depth below 20 

 fathoms as a marginal sea-cut scarp that has been submerged. A 

 similar steeply sloping facet is shown in the profile of the Australian 

 platform, text figure 12. The statement on the growth-rate of 

 corals shows that any known living coral reef could have grown 

 to its estimated thickness since the disappearance of the continental 

 ice sheets, calculated to have been between 10,000 and 30,000 years 

 ago; and finally, so far as definite information has been procured, 

 living offshore coral reefs are superposed on basement platforms that 

 have been recently submerged. I am entirely convinced that glacial 

 control is one of the most important factors in bringing about the 



1 Changes of sea level due to changes of ocean volume : Washington Acad. Scl. Jour., 

 vol. 5, pp. 445-446, 1915. 



