308 PROF. HULL, LL.D., F.E.S., ON THE SUBMEEGED TERRACES 



observance of the changes of depth, as indicated by the 

 soundings, that the features themselves can be recognised 

 and portrayed.* 



Throughout a distance of 500 miles from the vicinity of 

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

 the British platform terminates seaward along the margin of 

 a gi'and escarpment of 7,000 to 8,000 feet in height ; remark- 

 able for the steep descent of its flanks, which in some cases 

 are 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. 

 The general outline of the platform and escarpment will be 

 understood from the diagrammatic sections. (Figs. 1, 2, 3 

 and 4.) Off the coast of Scotland the escarpment is known as 

 the Vidal Bank.f Its upper margin here very closely coincides 

 with the 100-fathom line ; but on tracing the margin south- 

 wards it is found to gradually become deeper till opposite 

 the entrance of the English Channel, it nearly coincides 

 with the 180-200 fathom contours. The sections taken at 

 intervals from ofi" the Hebrides to the coast of France, at the 

 entrance to Bay of Biscay, will illustrate this general state- 

 ment. (See Plate, Figs. 1, 2, 3, 4.) 



No. 1. Drawn through Rockall to the Isle of Mull, 

 illustrates the form of the sea-bed near the head of the great 

 bay which here penetrates northwards into the plateau which 

 stretches from Scotland by Rockall 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 depth of about 1,350 fathoms or 

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

 7,500 feet approximately. 



No. 2. Represents the outline of the sea-bed west of 

 County Donegal, at Sheve Liag, which rises in a bold 

 headland of nearly 2,000 feet from the ocean. Here the 

 margin of the British platform is still closely represented by 

 the 100-120 fathom contour, and the escarpment descends 

 to the 1,000 fathom line, from which the floor of the ocean 



* The British platform is described by Professor Spencer, Geological 

 Magazine^ No. 403, p. 37 (1898). t Admiralty chart. 



