TT. H. Rudleston — E. Margin of N. Atlantic Basin. 149 



of 12,000 feet he claims for the coatinent of North America, and he 

 considers that the period of greatest elevation was early Pleistocene. 

 In speaking of what he calls the submerged plateau of the North 

 Atlantic, he points out that it rises northwards to the Iceland ridge ; 

 and according to his view the several channels or straits, to which 

 allusion has already been made, represent so many cols which, 

 presumably, were indented by meteoric erosion during the period 

 of principal emergence. He particularly mentions the col of the 

 channel between Faeroe and Shetland, corresponding to tlie lowest 

 depression of the Wyville Thomson ridge, as opening out into 

 a great valley which off the north-west of Ireland, he says, reaches 

 a depth of 9,980 feet. 



This of course must be the Rockall gulf or embayment. It is 

 not quite easy to follow the statements and reasoning of Professor 

 Spencer with reference to the inequalities in the bed of the ocean. 

 But if the bed of the North Atlantic has at any time since the 

 Middle Tertiary period undergone a general uplift of 12,000 feet, 

 it is obvious that the Rockall gulf must have been dry land ; and 

 it seems as though Professor Spencer would have us believe that 

 this gulf has been carved out like an ordinaiy valley during a period 

 of emergence. Apart from considerations as to the enormous length 

 of time which would be required to excavate a valley 9,980 feet 

 deep with sides sloping at a very moderate angle, it is much more 

 probable that the Rockall gulf, the Lightning Channel, and the 

 deeps of the Norwegian Atlantic are all due, in the main, to tectonic 

 causes acting along the general alignment of the Atlantic depression. 



Part III. — The British Atlantic and Bay of Biscay. 



Some of the hydrographical details supplied by the Admiralty 

 charts are now continued so as to include the South of Ireland, the 

 Bay of Biscay, and the north coast of Spain. It was originally 

 intended to extend the investigation as far as the Straits of Gibraltar, 

 but the paper is becoming longer than I expected, and the rest must 

 be dealt with briefly. 



A long finger of the Atlantic deeps penetrates the irregular 

 platform which is connected with the Porcupine ridge. This, for 

 the sake of distinction, I would call the ' Gulf of Munster.' Off 

 Bantry Bay the 100-fathom line and the 1,000-fathom line are 

 45 miles apart, giving an incline of 1 in 80, or considerably less 

 than one degree. Beyond Bantry Bay the 100-fathom line runs 

 nearly due south for 180 miles ; the contours are at first pretty v/ide 

 apart, but gradually become closer. A great change takes place in 

 the neighbourhood of the Sole banks, which lie from 150 to 200 miles 

 south of Cape Clear. Here the submerged continental platform 

 attains its greatest width, and the edge now curves round to the 

 eastward ; whilst the contours of the submerged continental slope 

 approach each other in a very irregular manner. 



Between the Sole banks and La Chapelle bank, off Ushant, are two 

 irregular indentations of the 100-fathoni line, which may represent 

 the discharge of the rivers of St. George's Channel and of the 



