156 W. H. Hiidleston — E. Margin of N. Atlantic Basin. 



land bordering the Porcupine bank, off the west of Ireland. But 

 the 100-fathom line is found for long distances to coincide fairly 

 well with that edge, beyond which the suboceanic slope plunges, 

 sometimes gradually, sometimes sharply, into abyssal depths. 



3. The suboceanic slope may be traced as a distinct feature, 

 though better defined in some places than in others, with a general 

 north-north-easterly trenci, as far as off the north-west of Spitzbergen, 

 where the trend becomes easterly in face of the North Polar ocean. 



4. The suboceanic slope is to be regarded as the true limit 

 between the continental area and the oceanic area, and the terri- 

 genous deposits appear, throughout geological time, to have been 

 confined to the region which lies within, i.e. to the eastward of, 

 this line. 



5. The great tectonic movements have been especially powerful 

 in alignment with the suboceanic continental slope at different 

 periods of the world's history ; and these movements have produced 

 extensive protuberances, which have yielded no inconsiderable 

 portion of the sediments deposited in the corresponding geosynclinal 

 hollows, thus constituting some of the great terrigenous formations. 

 The extensive development of old crystalline rocks in the countries 

 which border the North Atlantic probably represent portions of these 

 old protuberances. 



6. Although the line dividing the continental from the oceanic 

 area is fairly well defined throughout the region under consideration, 

 it is one of unequal strength, and appears to fail or to be deeply 

 deflected in certain places. Commencing on the north, the first 

 great embayment is represented by the mouth of the Barents Sea. 

 Here the coastline with its old crystalline rocks, of which there are 

 said to be considerable traces in the west of Spitzbergen, fails us 

 until we get to Norway. Similarly there is a great gap between 

 Norway and Scotland, the intervening area being represented by the 

 mouth of the North Sea. Both these embayments are occupied by 

 shallow seas and their connections, and they may be regarded as 

 belonofing^ to the continental area and to share its vicissitudes. Yet 

 it is probable that throughout a part, at least, of geological time they 

 have been the gateways whereby the waters of the ocean com- 

 municated with the various seas, where deposits since elevated into 

 dry land have from time to time been formed. 



Omitting the mouth of the English Channel, which possibly has 

 a different origin, the next great embayment is the Bay of Biscay, 

 and this differs fro^ the two previously mentioned by its great 

 depth. This seems to represent the gateway, whereby the waters 

 of the ocean communicated with the Mediterranean, though in the 

 present day the head of the gulf has been filled up by the Tertiary 

 deposits, which constitute so large a portion of the south-west of 

 France. Moreover, this area is complicated by the great tectonic 

 movements in connection with the Pyreneo-Cantabrian chain. The 

 gut of Gibraltar is probably a more recent feature, and may in part 

 be due to meteoric erosion at a time when the land was higher. 

 This also may have been the case with the Fosse de Cap Breton. 



