Daly — The Coral-Reef Zone. 141 



cation of certain ash-cones raised to the sea surface dur- 

 ing the nineteenth century ; nor as to the unlikelihood of 

 reef protection for an ash-cone island in the open ocean, 

 for a coral plantation would there be specially subject to 

 killing by sediment. 



Many other pre-Glacial islands must have been trun- 

 cated or strongly benched because their surrounding 

 waters were too muddy or sandy for coral growth. 6 

 This is now the case with a goodly number of islands in 

 the Eastern Archipelago. 



Coral Beefs at the Beginning of the Glacial Period. 



The paleontological record suggests that the late-Ter- 

 tiary was a time for reef growth probably as vigorous as 

 now, though perhaps far less extensive. The proper 

 degree of association of coral species with each other and 

 with algae, etc. seems to have been evolved already by 

 the beginning of the Cenozoic era, if not earlier. Reef 

 structures competent to resist the waves were thus pos- 

 sible, if the temperature and other physical conditions 

 were right. We may assume that some of the late-Plio- 

 cene shores were fringed with reefs. How long those 

 shores had been so protected against wave attack is 

 uncertain, inasmuch as, during the long Tertiary, there 

 may have been periods when the tropical seas were either 

 too warm or too cool for reef growth. If the conditions 

 of the early Pleistocene were the same as now, most 

 shores were reef-free, for at present about two-thirds of 

 the coast lines of continents and larger islands in the 

 warm, tropical ocean fail to show well-developed reefs. 7 

 Moreover, if a similar ratio of reef-free coasts charac- 

 terized the Tertiary period generally, wave abrasion 

 could have already produced very extensive shoals at the 

 beginning of the Glacial period. 



Tertiary fringing reefs would have been specially 

 developed on the capes or spur-ends between pairs of 

 drowned valleys occurring along shores of subsidence; 

 herein is a partial explanation of the uncliffed forms of 

 many such spur-ends at the present time. 



On the other hand, great abundance of atolls or barrier 



6 Sea-cliffs, the proofs of ancient benching', would have faded out, if, since 

 their cutting, their respective shores have been long protected by reefs. 



T Koughly 65,000 kilometers out of about 100,000 kilometers, measured on 

 L. Joubin's map of the coral reefs of the world. 



