On the Eastern Jlargin of N. Atlantic. 565 



As to the Eockall embayment and Lightning channels, it may be 

 said that only a brief notice was taken of these by nie in my pre- 

 liminary paper,^ cited by Mr. Hudleston. In a general way I called 

 attention to the deep valley-like depressions dissecting the submarine 

 Icelandic plateau in both directions. These and the Eockall embay- 

 ment. with their tributai'y amphitheatre-like valleys, were regarded 

 as only the more advanced forms of atmospheric sculpturing of the 

 margins of an elevated plateau, similar to land features, of which 

 plenty of examples can be given. But the occurrence of the sub- 

 marine plateau is explained by Mr. Hudleston as an igneous 

 •extravasation, while the dissection of the drowned barrier by deep 

 valleys he attributes to tectonic causes. But he does not even com- 

 pare the adjacent submarine features (as, for instance, the fjords and 

 their tributary amphitheatres) with like forms of the basaltic plateaii 

 of the Faroes, dissected into islands by valleys and fjords, with 

 •cirques of 2,000 feet in depth. Neither the hypothesis of the 

 general igneous origin of the Icelandic plateau barrier, nor that of 

 the tectonic origin of the valleys, subsidiary to the plateau formation, 

 does he support by evidence, and in substituting his explanations for 

 the hypothesis of subaerial sculpturing of a former land, he brings 

 back upon himself the onus probandi of sustaining his theory. 



Mr. Hudleston sums up eight conclusions, and these by themselves 

 would have been mostly accepted by Professor Hull and myself. 

 But the details of the paper appear more strongly to have for their 

 object the discrediting of the hypothesis of great changes of level of 

 Jand and sea. I thank him for the trouble he has undertaken in 

 'bringing out so many points, and producing such good illustrations. 

 It has enabled me to point out some of the methods of investigation 

 adopted by Professor Hull and myself, and I trust that it may be of 

 use to other students. But in nothing that he has shown does there 

 appear testimony against the correctness of conclusions by Professor 

 Hull concerning the great changes of level of western Europe in 

 late geological times. The evidence makes me believe with Professor 

 Hull that the submerged plateaux, with gently undulating topo- 

 graphy, or rounded and flattened forms, were old land surfaces, 

 largely brought into being by the laws governing the base-level of 

 erosion during the very long Mio-Pliocene period. Some of the 

 broader valley features may have been produced during some portion 

 of the same period, but, generally speaking, our theory is that the 

 deep channels dissecting the drowned plateaux were formed during 

 a subsequent epoch of high continental elevation, or were reopened 

 and enlarged in it. The evidence in America places the great 

 elevation after the time of the establishment of the modern molluscan 

 life, but before the epoch of the accumulation of the glacial deposits : 

 approximately, about the commencement of the Pleistocene Period. 

 Then the older valleys were being enlarged, and the bounding slopes 

 ^vere being dissected by receding caiions and amphitheatres, which 



' Eead before the Meeting of the British Association, 1S97 : Geol. Mag., 

 Dec. IV, Yol. V (1898), pp. 32-38. 



