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VIII—ON THE GEOLOGICAL AGE OF THE NORTH ATLANTIC OCEAN. 
By EDWARD HULL, LL.D. F.R.S, F.G.8., Director of the Geo- 
logical Survey of Ireland. (Plates VII. and VIII.) 
[Read, June 16, 1884.] 
INTRODUCTORY. 
Tue determination of the age of our continents and oceans will ever be a problem 
of the highest interest in physical inquiry, and has recently occupied the attention 
of several eminent leaders in cosmical investigation, amongst whom may be 
specially named Professor Dana,* Professor Le Conte,t and Dr. Wallace. The 
views of these observers are more or less in accord; and they agree in considering 
the continents on the one hand, and the oceans on the other, to be of immense 
antiquity—almost dating back to the original consolidation of the earth’s crust. 
Stated in brief, these authorities hold the doctrine of “the permanency of oceans 
and continents.”{ Against this may be placed the doctrine of ‘the repeated 
interchange of oceans and continents,” of which Lyell is the chief exponent.§ The 
differences between the views of these two schools are fundamental ; for while those 
of the former maintain that the continents and oceans were marked out in their 
main features, and their geographical positions roughly determined, before the 
introduction of life on the globe, Lyell maintains on the other hand that ‘the 
configuration of the earth’s surface has been remodelled again and again since it 
was the habitation of organised beings, and that the bed of the ocean has been 
lifted up to the height of some of the loftiest mountains.” Again, he says, ‘It 
is not too much to say that every spot which is now dry land, has been sea at some 
former period; and every part of the space now covered by the deepest ocean has 
been land.” This last paragraph especially shows how unreservedly Lyell held 
the doctrine of the “interchangeability of oceans and continents”: for myself, 
while I accept the former part of the thesis, I doubt much if the latter is true. 
It cannot be said that the modern ideas of the permanency of oceans and 
continents have arisen in consequence of any recent discoveries regarding the 
* Silliman’s *‘ Amer. Journ. Science,” vol. v. p. 423, &e. 
+ ‘Elements of Geology,” and ‘‘ Amer. Journ. Science,’’ vol. vi. p. 161, &e. 
+ An able review of these opinions and speculations, by Mr. W. O. Crosby, appears in the “ Geol. 
Magazine,” June 1883. Dana says, ‘‘ The above stated effects of contraction lead me to the conclu- 
sion that the oceanic and continental areas were defined when the earth’s crust first began to form, if 
not still earlier, during the progress of its nucleal solidification.” 
§ “Principles of Geology,’’ vol. i. chap. 12, edit. 1867. 
TRANS. ROY. DUB. SOC., N.S. VOL, IIL. 28S 
