%":■• EVOLUTION OF OCEANS AND CONTINENTS. 509 



merely the other extreme of the swinging pendulum of scientific 

 imagination. 



Recent discoveries of oceanic deposits, such as must apparently 

 have been formed in depths of from 1,500 to 2,000 fathoms, and 

 including representatives both of " red clay " and radiolarian ooze, 

 but now raised high above the level of the sea within the limits of a 

 continental plateau, have shown the danger of depending on negative 

 eyidence. Again, a more accurate knowledge of submarine contours 

 and the exigencies of explaining the distribution of animals have 

 obliged Dr. Wallace to include much greater depths within the 

 regions of possible interchange. He now says : " All that is neces- 

 sary to maintain therefore is, that existing continents with their 

 included seas and their surrounding oceanic waters as far as the 

 1,500-fathom, or in some extreme cases the 2,000-fathom line, mark 

 out the areas within which the continental lands of the globe have 

 been built up ; while the oceanic areas beyond the 2,000-fathom line, 

 constituting, according to Mr. Murray's data, 71 per cent, of the 

 whole ocean, have almost certainly been ocean throughout all known 

 geological time." 



This is a great concessioni and the " almost certainly " may 

 foreshadow further admissions ; 71 per cent, is very different from 

 92 per cent., and the extension of interchangeable areas to regions 

 within the 2,000-fathom line enables us at once to speculate on the 

 possibility of a former antarctic continent with such extensions 

 toward New Zealand, South Africa, and South America as will 

 explain the curious points of similarity in the modern faunas of these 

 countries. The existence of such a continent has already been 

 suggested by Dr. W. T. Blanford.^ Dr. Wallace's present view also 

 enables us to assume the former existence of a large continent in the 

 Western Pacific with extensions southward to New Zealand and 

 westward to Australasia. It also gives us great possibilities of 

 change in the Atlantic Ocean, though hardly sufficient to account for 

 all the palaeontological evidence which has been or can be adduced in 

 favour of old connections between the more - tropical parts of Africa 

 and America. 



So far, therefore. Dr. Wallace has departed from the extreme 

 views which have been held by the writers whom he quotes with 

 approval, and which he upheld even in the second edition of his 

 " Island Life," published only a few months ago. He therein argues 

 against the deep-sea origin of chalk, and repeats the very erroneous 

 statement that '' deposits uniform in character and more than 150 or 

 200 miles wide were rarely, if ever, formed at the same time." Why 

 does he vainly endeavour to deny the close similarity between chalk 

 and foraminiferal ooze when in a later chapter he contemplates 

 submergences of more than 1,000 fathoms in extent ? 



- Pres. Address to Geol. Soc, 1890, p. 104. 



