Correspondence — Professor E. Hull. 133 



(2) Next, with regard to the formation of the Grand Declivity 

 by subaerial action, I now see where the obscurity of my language 

 le'i Mr. Jukes-Browne to misunderstand my meaning when he says, 

 " How the existence of river-made valleys can possibly prove the 

 declivity to have been made by subaerial agencies passes my com- 

 prehension." But Professor Spencer,' as also Mr. Fisher, have 

 recognized that under the term ' subaerial agencies ' I included the 

 erosive action of waves and currents along lines of cliff, whether 

 of emerging or subsiding land, just as we see along our own coasts 

 at the present day. In endeavouring to maintain, against some 

 objectors, that these sub-oceanic features were produced under the 

 air rather than under the waters of the ocean, I lost sight, for the 

 moment, of the very obvious fact that rivers and waves were 

 the chief agents in their formation. I hope I have now made my 

 meaning clear ; but before leaving this point, I wish to add that, 

 although both during emergence and subsidence the action of the 

 Atlantic waters in cutting back the coast was doubtless in operation, 

 it seems most probable that the greatest amount of work was done 

 during the doubtless prolonged pause which intervened when the 

 change from the one direction of movement into the other was taking 

 place ; during this period, also, river-erosion was probably most 

 active. 



(3) The last important point on which I shall touch is with 

 reference to the geological age of these sub-oceanic features. I have 

 assumed that it was during the prolonged period extending from the 

 close of the Eocene into the Post-Pliocene. Mr, Jukes-Browne asks, 

 " Is there any reason why the formation of the escarpment and the 

 union of Great Britain with Iceland should not have taken place in 

 the Eocene period?" (Geol. Mag., 1898, p. 430). Doubtless, there 

 was an incipient uprising and shaping of our coasts at this epoch, as 

 indicated by the discordant relations of the Lower Tertiary to the 

 Cretaceous strata. But, while admitting with Mr. Jukes-Browne the 

 probability of an incipient uplift, I strongly hold that it was not till 

 the succeeding Miocene stage that the great elevatory movement of 

 the Atlantic bed determinately set in. The powerful terrestrial 

 movements during this and the succeeding Pliocene age, all over the 

 European area and beyond, accompanied by denudation, need not here 

 be insisted on. But the point which concerns our present inquiry is 

 this : that the courses of the existing British and Continental streams 

 having been mainly determined during these later Tertiary periods, 

 we have a clue to the age of those now under the ocean, as they 

 were once in physical connection with them. The subject is, 

 however, too wide and intricate to be fully dealt with here ; 

 and I must hasten on to my last point, namely, the epoch of 

 maximum elevation ; and in answer to the second part of Mr. Jukes- 

 Browne's question (quoted above), I reply, that whether or not 

 this connection was established in the Eocene period, it is clear 

 that it was continued (or repeated) in Pleistocene times, inasmuch as 



1 Geol. Mag., January, 1899, p. 17. 



