W. M. Davis — Shaler Memorial Study of Coral Reefs. 259 



about 1000 feet ; thus the total submergence to be accounted 

 for becomes formidable. 



Possible Causes of Submergence. — As for the second consid r 

 eration, a rise of sea level resulting from an increase in the 

 volume and depth of the ocean through the addition of water 

 that escapes from deep within the earth bj volcanic eruptions 

 and otherwise seems entirely inadequate to cause the submerg- 

 ence demanded by coral reefs ; all the more inadequate when 

 it is remembered that some decrease of ocean volume and depth 

 might be caused at the same time by the retention of rainwater 

 in the continental masses by the hydration of previously non- 

 hydrous minerals. 



A more available cause for a rise of sea level can be imagined 

 in an upheaval of part of the ocean bottom, as in the upper 

 section of fig. 8, and the possibility of such upheaval is clearly 

 indicated by the occurrence of elevated coral reefs on various 

 islands. But there are certain general considerations which 

 make it extremely improbable that the submergences, in asso- 

 ciation with which coral reefs have been formed, are to be thus 

 explained in any large measure. In the first place this cause 

 of submergence is, like the preceding, a wasteful one, for it 

 raises the ocean surface everywhere ; it is indeed an extrava- 

 gantly wasteful cause, for the measure of ocean-bottom uplift 

 must be greater than the necessary submergence in the ratio 

 that the area of ocean-bottom uplift is smaller than the entire 

 ocean-bottom ; if the area of uplift is one-twentieth of the ocean 

 area, the uplift must be 6000 feet in order to raise the ocean 

 surface 300 feet. Evidently one who regards Darwin's theory 

 of subsidence as demanding excessive deformation of the ocean 

 floor cannot find satisfaction in this alternative theory. In the 

 second place, this cause is, like the preceding, an involved one, 

 for it requires a uniform and contemporaneous submergence 

 of all the shorelines of the world, except where local counter- 

 balancing deformation occurs. In the third place, the uplift 

 of a certain area of the earth's crust without any compensat- 

 ing subsidence of an adjacent part demands the improbable 

 assumption that the uplift is due to increase of volume only in 

 that part of the earth's mass which lies beneath the uplifted 

 area ; it is more reasonable to suppose that the rise of the 

 uplifted area involves a roughly compensating subsidence of 

 some other area, the two movements being connected by a 

 lateral transfer of material at some unknown depth within the 

 earth. In the case here considered, the least extravagant 

 arrangement of the compensating movements would be to have 

 the area of uplift entirely beneath the ocean, and the area of 

 subsidence entirely within a continent, as in the upper section 

 of fig. 8 ; for then the subsidence would not, by tending to 



