Bordering the British Isles. 353 



observei's already referred to.^ Indeed, all the evidence obtainaMe 

 by soundings goes to show that the whole area of the North 

 Atlantic has undergone stupendous changes of level in A'ery recent 

 times both as regards emergence and submergence. 



III. The British Platform. — The submerged terrace on which the 

 British Isles and adjoining portions of Europe are planted is 

 generally known as " the 100-fathom platform." It is often 

 represented on hydrographical charts, such as those of the late 

 Professor Sir Wyville Thomson, by the 100-fathom contour taken 

 from the Admiralty Chart.- But this strict adherence to the 100- 

 fathom contour is misleading as regards the great physical features 

 of the submerged lands ; and the same observation applies to the 

 other contours. These features undergo elevation and. depression 

 according to geographical position ; and it is only by a close 

 observance of the changes of depth, as indicated by the soundings, 

 that the features themselves can be recognized and portrayed.' 



Throughout a distance of 500 miles from the vicinity of Kockall 

 on the north to the entrance of the Bay of Biscay, the British 

 platform terminates seaward along the margin of a grand escarpment , 

 of 7,000 to 8,000 feet in height and remarkable for the steep descent 

 of its flanks ; in some cases precipitous. The edge of this escarpment 

 is quite sharp, and well-defined by the sudden descent of the 

 soundings ; and at, or towards, its base it gives place to' the abyssal 

 plain with a very gentle descent towards the oceanic bottom. Oil the 

 coast of Scotland the escarpment is known as the Vidal Bank. Its 

 upper margin very closely coincides with the 100-fathom line, but 

 on tracing the margin southwards it is found to gradually become 

 deeper, till opposite the entrance of the English Channel the margin 

 nearly coincides with the 180-200 contours. The following sections 

 taken at intervals from off the Hebrides to the coast of France, at the 

 entrance to the Bay of Biscay, will illustrate this general statement.* 



No. 1. Drawn through Kockall to the Isle of Mull, illustrates 

 the form of the sea-bed near the head of the great ba}'^ which here 

 penetrates northwards into the plateau, which stretches from 

 Scotland by Eockall towards Iceland, on which the Faeroe Islands 

 and Orkneys are also planted. The margin of the British platform 

 is sharply defined by the 100-fathom contour at about 70 miles from 

 Uinst, at which point the escarpment descends at a steep angle to the 

 1,000-fathom contour, where it gives place to the abyssal floor of 

 the ocean, descending to a further depth of about 1,350 fathoms or 

 8,100 feet. The total height of the escarpment is here 7,500 feet 

 approximately. 



No. 2. Kepresents the outline of the sea bed west of County 



1 I have given a short preliminary notice of the results of my examination of the 

 Admiralty charts in Nature, March 24th, 1898. 



2 '• The Depths of the Sea," pis. ii, iv, v (1873). 



^ The British platform is described by ]?rofessor Spencer, Geological Magazine, 

 No. 403, p. 37 (1898). 



* The sections here described are drawn on the plate which accompanies the 

 original memoir in the Trans. Vict. Inst., vol. xxx, 1898. 



DECADE IV. VOL. T. — NO. VIII. 23 



