38 STUDIES, SCIENTIFIC AND SOCIAL chap. 



with any general interchange of oceanic and continental 

 areas, or which render it exceedingly difficult to under- 

 stand how such interchange could have been brought 

 about. These phenomena are : — (1) The enormous dis- 

 proportion between the mean height of the land and the 

 mean depth of the ocean, which would render it very 

 difficult for new land to reach the surface till long 

 after the total submergence of the sinking continent. 

 (2) The wonderful uniformity of level over by far the 

 greater part of the ocean floor, which indicates that it is 

 not subject to the same disturbing agencies which through- 

 out all geological time have been creating irregularities 

 in the land-surface, irregularities which would be far 

 greater than they are were they not continually counter- 

 acted by the lowering and equalising effects of subaerial 

 denudation. (3) The remarkable parallelism and com- 

 pleteness of the series of geological formations in all the 

 best known continents and larger continental islands, 

 indicating that none of them have first risen from the 

 ocean floor during any portion of known geological history, 

 a conclusion enforced by the absence from any of them of 

 that general deposit of oceanic ooze at some definite 

 horizon, which would be at once the result and the proof 

 of any such tremendous episode in their past history. 



I submit that these facts, and the conclusions to be 

 logically deduced from them, form a very powerful, if not 

 a conclusive argument as against those who maintain the 

 interchange of continents and oceans as a means of explain- 

 ing certain isolated geological or biological phenomena; 

 such, for instance, as the much-disputed origin of the 

 chalk, or the supposed necessity for land-communication 

 to explain the distribution of certain groups of mammals 

 or birds, reptiles or fishes in remote geological times. 

 Before postulating such vast revolutions of the terrestrial 

 surface in order to cut the gordian knot of difficulties 

 which may be mainly due to imperfect knowledge, it will 

 be necessary to show that the considerations here adduced, 

 as well as the great body of facts which have caused many 

 eminent geologists, naturalists, and physicists to hold the 

 doctrine of oceanic permanence, are either illogical or 



