PEKMANENCE OF CONTINENTS AND OCEANIC BASINS. 127 



cially during the cainozoic period, is well known ; but even if 

 the surface of the oceans were to sink from one thousand to 

 eighteen hundred fathoms, it would still be possible to recognize 

 in the rough the present outline of our continents. Hence it 

 would seem as if that outline were intimately connected with 

 their earliest appearance and the subsequent evolution of the 

 continent, and that these masses are not merely due to acciden- 

 tal denudation. 



The view of the sfreat ag-e of our continents and oceanic 

 basins was probably first suggested by Guyot ; it was indepen- 

 dently taken up by Dana, and Agassiz was perhaps the first to 

 show that the results of the earlier deep-sea dredging expedi- 

 tions added materially to the correctness of this view. Subse- 

 quently Thomson, Geikie, and Carpenter elaborated this theory, 

 which of late has gained ground among geologists, and has 

 found its most recent advocate in Wallace. 



The o-eoloofical structure of the different islands of the world 

 enables us to judge whether they are mere volcanic peaks, the 

 highest points of districts subject to cataclysmic local elevations, 

 or whether they are parts of larger masses of land first built up 

 by sedimentary deposits,^ and gradually reduced by denudation 

 to their present size, — the remains, in fact, of great submarine 

 banks, indicating in a certain measure the former outlines of 

 the land. The extent of this denudation has been calculated 

 in some cases ; and so powerful is its agency, that, if carried on 

 during long periods of time, it may transform oceanic regions 

 into continental masses, and the reverse. This may have been 

 the case in the earliest periods of the formation of the earth's 

 crust, when the precipitation was much greater than now ; but 

 we have as yet no evidence of any such transposition of conti- 

 nental masses and of oceanic basins since the mesozoic period. 

 If such pre-archsean continents existed, they, like the continents 

 from which the materials for the mesozoic and tertiary deposits 

 were derived, have left no traces. 



^ The careful examination of St. Paul's having, as shown by Geikie, nothing what- 



rocks by the Abb^ Renatd, for instance, ever to do with the remains of a former 



clearly proves this island to be of volcanic continent, the long lost Atlantis, 

 origin, like many other oceanic islands. 



