CHAP. XV.] OF CONTINENTS AND OCEANS. 333 



logical evidence as we possess is certainly in favour of there 

 having been a large area of land on the site of the North 

 Atlantic Ocean during part of Palaeozoic time, but how far 

 this land trenched on the deeper parts of the Atlantic we 

 have no means of knowing. I agree, therefore, with 

 Professor Prestwich, who has recently expressed the 

 opinion " that it is only the deeper portions of the great 

 ocean-troughs that can claim the high antiquity which is 

 now advocated for them by many eminent American and 

 English geologists." ] 



Stated in general terms, the conclusion at which we have 

 arrived may be expressed as follows : That while the posi- 

 tion of our modern oceans and continents has not been 

 permanent from the earliest geological times, they are 

 nevertheless of very ancient date ; and we may infer that 

 the replacement of an ocean by a continent, or vice versa, is 

 a process which has not taken place many times in the 

 history of any one portion of the earth's surface. 



To my mind, indeed, the study of the geological evidence 

 suggests an inference which is different from either of the 

 theories which have been discussed. It has already been 

 observed that the absence of anything like deep oceanic 

 deposits among the Palaeozoic rocks may be taken as in- 

 dicative of a great difference in the general relations and 

 proportional areas of land and sea, the probability being 

 that there were neither oceans nor continents like those 

 which now exist, but an irregular distribution of compara- 

 tively shallow seas among land-tracts of moderate eleva- 

 tion. In Neozoic times we find proof of the existence of 

 oceans, though these do not seem to have been so deep as 

 those of the present day ; that there were also large tracts 

 of continental land is proved by the traces of large rivers 

 and large inland lakes, but so far as we know these land- 

 tracts did not form the nuclei of the modern continents of 

 1 Prestwich 's " Geology," vol. ii. p. 547. 



