154 Scientific Intelligence. 



duration whicli is held to be necessary to explain barrier reefs 

 and atolls in true oceanic regions. 



The author suggests that a test of this hypothesis would be the 

 finding of reef-crowned islands which had sunk to considerable 

 depths, but admits that so far the evidence in this direction is 

 scanty. He presents one case, however, in the Ceram sea which 

 is held to be in the nature of the desired proof. It is obvious 

 also that the hypothesis should apply to all volcanic islands that 

 rise from the oceanic ab^^sses wherever thej may be found. In 

 the Atlantic only Bermuda is held to fill this definition, and to be 

 in the area of reef -building corals, and the fact that reef limestone 

 was found in a boring on it to extend to the depth of 245 feet 

 below present sea-level is viewed as agreeing with the hypothesis. 



The reviewer, who desires to say at the outset that he has no 

 bias toward an}^ particular theory as to the formation of coral 

 islands, offers the following comments on this hypothesis. In the 

 first place the work which has been done in recent years upon the 

 strength of rocks in resisting deformation precludes the idea that 

 a basaltic cone could flatten out by its own weight. There might 

 be some lowering by the compacting of fragmental or vesicular 

 material, but this effect should take place largely in measure as 

 the cone grew and would soon cease. A volcanic cone of itself 

 must be regarded as a competent structure. If the sinking takes 

 place it must be by a yielding of the foundation on which it is 

 placed and of the cone as a whole. 



It cannot be supposed that a yielding basaltic stratum can 

 immediately underlie the sea. Moreover, a distinction must be 

 made between material that is rock, that is a rigid solid, and that 

 which is in any sense liquid or initially plastic. The floor under- 

 lying the sea must be of rock and it cannot be plastic until a depth 

 has been reached where the resistance to deformation has been 

 overcome. The experiments of Adams show that under labora- 

 tory conditions the crust increases in strength with depth. Or, 

 on the other hand, if plasticit}^ is to be referred to a change of 

 rock from the solid to the liquid condition, this also can only 

 occur at a depth where increasing heat is sufficient to overcome 

 the effect of pressure, and this can be no relatively slight one. It 

 is clear from this, therefore, that if the volcano sinks bodily into 

 the sima, large underlying masses of the crust on which it stood 

 must also be involved in the movement. It is also questionable 

 whether a mass of tightly fitted earth blocks resting either on a 

 liquid substratum, or one rendered plastic by deformative stress, 

 would not be competent to sustain the volcanic load under the 

 static conditions posed in the hypothesis. In order to have sub- 

 sidence, it would seem as if differential movements in the yielding 

 substratum must occur. But if these took place on a small scale 

 they would be attended by outflows and quick readjustment, while 

 the hypothesis does not permit us to assume undertow move- 

 ments on a large scale leading to orogenic processes. It is dif- 

 ficult to see how such subsidence as is demanded could occur 

 without diastrophism. 



