AUGUST. jj^E PERMANENCE OF OCEANIC BASINS. 419 



and at many different epochs; and, having arrived at the conclusion 

 that the distribution of organisms could be more harmoniously and 

 consistently explained without such changes of sea and land, which 

 usually created greater difficulties than those they were intended to 

 explain, I gave, in my " Island Life " a brief statement of the 

 evidence which appeared to me to render such changes exceedingly 

 improbable. This evidence was mainly a summary of the facts and 

 arguments adduced by the eminent men referred to above, and to 

 this I added in my " Darwinism " a difficulty founded on mechanical 

 considerations which seemed to me to furnish a preliminary reason 

 why we should not accept the doctrine of the interchange of con- 

 tinental and oceanic areas without very clear and cogent reasons. 

 Since then some other arguments of this nature have occurred to 

 me, and as the theory of permanence has been recently attacked, by 

 Mr. W. T. Blanford in his presidential address to the Geological 

 Society in 1890, and by Mr. Jukes-Browne in his " Building of the 

 British Isles," it may be as well to consider these difficulties, which 

 furnish, in my opinion, a very powerful argument against the inter- 

 change of oceanic and continental areas, and which has the advan- 

 tage of not requiring any knowledge of the higher mathematics in 

 order to estimate its validity. 



And, first, it is necessary to clear away some misconceptions as 

 to the proposition I really uphold, since arguments have been 

 adduced which in no way affect that proposition. Thus, Mr. Jukes- 

 Browne quotes Professor Prestwich as saying, " It is only the deeper 

 portions of the great ocean troughs that can claim the high antiquity 

 now advocated for them by many eminent American and English 

 geologists." But this is all that is claimed. For practical purposes I 

 at first took the 1,000-fathom line as, generally and roughly, indicating 

 the separation between the oceanic and the continental areas, because 

 at that time it did accurately divide the continental from the oceanic 

 islands, as defined by a combination of geological and biological 

 characters. It has, however, been since shown that two ancient 

 continental islands — Madagascar and New Zealand — are separated 

 from their respective continents by depths of more than 

 1,000 fathoms. We must, therefore, go as far as the 1,500-, or, 

 perhaps, in a few cases, to the 2,000-fathom line, and this will surely 

 mark out " the deeper portions of the great ocean basins," since 

 only isolated areas exceed 3,000 fathoms. 



Now, if we look at the deep ocean basins marked out by the 

 2,000-fathom line, not on Mercator's projection which greatly 

 exaggerates the shallower portion situated in the temperate and polar 

 regions, but on an ^qual-area projection, such as the map which 

 illustrates Mr. J. Murray's paper, ^ we shall see that by far the larger 

 part of all the great oceans are included by this line, and that, for 



1 " On the Height of the Land and the Depth of the Ocean," Scottish 

 Geographical Magazine, 1888. 



