On the Eastern Margin of N. Atlantic, 561 



Islands ') all the known land and presumably most of the submerged 

 land is of igneous origin." This last conclusion, applied to a barrier 

 nearly a thousand miles long and hundreds of miles in width, seems 

 to me a more extravagant conclusion than the amount of changes of 

 level postulated by Professor Hull and myself. The central 

 American barrier, between the Caribbean Sea and the Pacific Ocean, 

 is of even smaller proportion, and those parts of it which are above 

 water show a prevalence of volcanic rocks of comparatively recent 

 date ; yet from beneath these rocks old crystallines are occasionally 

 exposed, and remains of the earlier Tertiary formations are widely 

 distributed. So, too, it is hardly justifiable to suppose that there is 

 no diversity of formations on the Icelandic plateau, which would 

 suggest continental features ; accordingly, the student of submarine 

 topogi-aphy is forced to analyze the land-like forms of the ridge, all 

 the more so as the valleys and their tributaries, cirques, and embay- 

 ments suggest that they were fashioned in the same manner as other 

 submarine and subaerial valleys, far away from great plateau 

 eruptions. 



A third feature noticeable in the paper is a general overlooking o£ 

 the detailed form of the edge of the platform, where the soundings. 

 '' are very irregular and puzzling, so much so that it is not easy to 

 deduce any mean angle of inclination." There is no special reasoa 

 why a mean slope should be found. It is the study of such 

 "curious and perplexing" features which has given rise to the bold 

 hypothesis of tremendous changes of level of land and sea. There- 

 fore, so long as Mr. Hudleston overlooks the amphitheatres and 

 valley-like indentations of thousands of feet in depth, dissecting the 

 continental margins, he has not the facts before him to warrant 

 the ex cathedra conclusion — that stupendous changes of level have 

 not occurred. 



However, Mr. Hudleston has spoken of the Norwegian channel 

 from the Skager Eack, which has long been known and written 

 upon. Its breadth seems to be greater than he is prepared to accept 

 as that of a valley, although it is a strong feature from Christiania, 

 Fjord, rounding the point of Norway, and extending 500 miles to 

 the oceanic abyss. Its breadth should be no difficulty, for it is not 

 as great as that of the lower St. Lawrence merging into the Gulf of 

 the same name ; and the flood plains of the land-valley of the lower 

 500 miles of the Mississippi are from 30 to 80 miles wide, with its 

 lower portion now buried by sediments to a depth of 1,000 feet. 

 This Norwegian channel has a depth, near its head, of 2,658 feet, 

 but farther seaward, as it is crossing the subcoastal plain, its depth 

 is reduced to 960 feet, unless the soundings do not reveal the deepest 

 portions of the channel. He considers this feature " unfortunate " for 

 the theory of its being the course which drained the Baltic valley, 

 and says : " the river of the Baltic, therefore, must have had some 

 difficulty draining towards the Atlantic under these circumstances." 

 Professor Hull and Professor Bonney have answered these points. 

 As shown by them, it is in a region of glacial distribution ; so 

 that an easy explanation is seen in the unequal filling of the old 



DECADE IV. VOL. VI. — NO, XII. 36 



