30 STUDIES, SCIENTIFIC AND SOCIAL chap. 



knowledge of the higher mathematics in order to estimate 

 its validity. 



And, first, it is necessary to clear away some misconcep- 

 tions as to the proposition I really uphold, since arguments 

 have been adduced which in no way affect that proposi- 

 tion. 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 al the deep ocean basins marked out 

 by the 2,000-fathom line, not on Mercator's projection 

 which greatly exaggerates the extent of the shallower 

 portion situated in the temperate'and polar regions, but on 

 an equal-area projection, such as the map which illustrates 

 Sir J. Murray's papsr,^ we shall see that by far the larger 

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

 that, for the purpose of indicating the isolation of the con- 

 tinents from each other throughout the equatorial and 

 most of the temperate zones, there is very little to choose 

 between the 1,000-fathom or the 2,000-fathoni boundary. 

 The latter, however, allows more scope for possible land 

 extensions between the three southern continents and the 

 Antarctic lands, which, during mild epochs, and by means 

 of intervening islands, may, perhaps, have served as a 



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

 Geographical Magazine, 1888. 



