W. H. Hudleston — E. Ifargin of N. Atlantic Basin. 147 



Norwegian Atlantic, to meet on the other side of the ridge the great 

 ernbayment of the British Atlantic, which lies betwixt Ireland and 

 the Rockall platform. 



Throughout this part of the ocean the suboceanic continental slope 

 is not always to be made out with certainty. It is very jperceptible 

 off Romsdal in Norway, but less distinct between that coast and 

 Shetland, off the mouth of the North Sea. Here the contours are 

 more gradual even than off the mouth of the Barents Sea. Never- 

 theless, it is within this marginal slope that all the terrigenous 

 deposits lie, whilst outside, i.e. to the westward beyond the centre of 

 the Lightning Channel, all the known land, and presumably most of 

 the submerged land, is of igneous origin.^ According to my view, 

 the continuation of the suboceanic continental slope is to be found 

 along the south-east side of the Lightning Channel, which is tolerably 

 steep in places. Thus, about 55 miles W.N.W. of St. Magnus Bay, 

 in the mainland of Shetland, the edge of the Continental platform 

 lies in about 90 fathoms of water ; from this edge the submarine 

 slope descends to 640 fathoms in the space of 15 miles, showing an 

 inclination of 1 in 24, or 2^°. This is the steepest declivity I can 

 find in connection with the Lightning Channel. 



South of the Wyville Thomson ridge the suboceanic continental 

 slope may be traced in the Vidal bank, which runs parallel with the 

 Hebrides ; here the contours are rather wide apart and the inclination 

 is gradual. The Vidal bank forms the eastern margin of that great 

 ernbayment of the Atlantic which runs up between Scotland and 

 Rockall. The Rockall bank is evidently of igneous and not of 

 terrigenous origin, and may be classed among the group of oceanic 

 islands ; it is probably in alignment with the Faeroe bank, 280 miles 

 towards the north-west, though never actually connected with it. 

 The rock itself is only 70 feet above the surface of the water, and 

 consists of an acid igneous product, named by Professor Judd 

 * rockallite,' but most of the specimens dredged from the bank are 

 said to be of basaltic character. (Trans. Roy. Irish Acad., xxxi, 

 1897, p. 39.)2 



Following the submerged continental slope in continuation of the 

 Vidal bank, a considerable change is noted off the coast of 

 Connaught, where the contours close in rapidly, and a deep 

 ernbayment of the Atlantic approaches within 80 miles of Broad- 

 haven. South of this embayment there is a large submerged 



1 Dr Thoroddsen (" Exploration in Iceland ") speaks of fragments of a tableland, 

 originally connected, forming a 3,000 feet thick layer of breccia, which covered the 

 whole inner surface of Iceland, and which has been for the most part removed by 

 erosion ; the strata underlying the breccia is everywhere Tertiary basaJt. Un- 

 fortunately, the author does not say of what the breccia consists. (Geographical 

 Journal, November, 1898, p. 497.) 



Postscript. — In a letter dated Copenhagen, December 12, 1898, Dr. Thoroddsen 

 states that he refers to the ancient volcanic palagonite breccia with smaller and 

 larger fragments of basalt, dolerite, etc. It is obvious, therefore, that, so far as 

 we kni)W, all the materials which go to form this large island are of igneous origin, 

 not excepting the Tertiary leaf- beds, which appear to owe their mechanical sediments 

 exclusively to this source. 



2 For a notice of Rockall, see infra, p. 163. 



