Presidential Address. 223 



the ocean are necessarily those of greatest folding and con- 

 sequent elevation. We have thus a hard, thick, resisting 

 ocean-bottom which, as it settles down toward the interior, 

 under the influence of gravity, squeezes upward and folds 

 and plicates all the soft sediments deposited on its edges. 

 The Atlantic area is almost an unbroken cake of this kind. 

 The Pacific area has cracked in many places, allowing the 

 interior fluid matter to exude in volcanic ejections. 



It may be said that all this supposes a permanent con- 

 tinuance of the ocean-basins, whereas many geologists postu- 

 late a mid- Atlantic continent l to give the thick masses of 

 detritus found in the older formations both in Eastern 

 America and Western Europe, and which thin off in pro- 

 ceeding into the interior of both continents. I prefer, with 

 Hall, to consider these belts of sediment as, in the main, the 

 deposits of northern currents, and derived from Arctic land, 

 and that like the great banks of the American coast at the 

 present day, which are being built uj) by the present Arctic 

 current, they had little to do with any direct drainage from 

 the adjacent shore. We need not deny, however, that such 

 ridges of land as existed along the Atlantic margins were 

 contributing their quota of river-borne material, just as on 

 a still greater scale the Amazon and Mississippi are doing 

 now, and this especially on the sides toward the present 

 continental plateaus, though the greater part must have 

 been derived from the wide tracts of Laurentian land with- 

 in the Arctic Circle or near to it. It is further obvious that 



1 Among American geologists, Dana and Le Conte, though from 

 somewhat different premises, maintain continental permanence. 

 Crosby has argued on the other side. In Britain, Hull has elabo- 

 rated the idea of interchange of oceanic and continental areas in 

 his memoir in Trans. Dublin Society, and in his work entitled The 

 Physical History of the British Islands. Godwin - Austin argues 

 powerfully for the permanence of the Atlantic basin, Q. J. Oeol. 

 Society, vol. xii. p. 42. Mellard Reade ably advocates the theory 

 of mutation. The two views require, in my judgment, to be com- 

 bined. More especially it is necessary to take into the account the 

 existence of an Atlantic ridge of Laurentian rock on the west side 

 of Europe, of which the Hebrides and the oldest rocks of Wales, 

 Ireland, Western France, and Portugal are remnants. 



