TF. H. Hudleston — E. Margin of N. Atlantic Basin. 155 



period down to the Pleistocene, when the coastline of the British 

 platform is represented as coinciding with the contour of 80 fathoms. 

 The strongest case for a canon is undoubtedly the Fosse de Cap 

 Breton at the head of the Gulf of Gascony, the leading bathymetrical 

 features of which I have already briefly described. Here, as we 

 know, the 100-fathom platform is cut through to a depth of 

 600 fathoms ; and if this be due to ordinary river erosion consequent 

 on emergence, it implies an elevation of between 3,000 and 4,000 feet 

 at this particular place. It is singular that this well-marked 'fosse' 

 should occur almost exactly in the angle formed by the French and 

 Spanish shores of the Bay of Biscay. If it be really due to river 

 action it may represent the effects of the accumulated waters 

 draining the northern slopes of the Pyrenees. It must not be for- 

 gotten, however, that the south-west of France represents a Tertiary 

 basin, and that throughout the greater part of Tertiary time there 

 must have been something like a connection between the Bay 

 of Biscay and the Golfe du Lion, which has obviously formed 

 the principal communication between, the Mediterranean and the 

 Atlantic. The difficult}^ is further complicated by the fact that 

 both the Fosse de Cap Breton and its supposed prolongation opposite 

 Bilbao are within the tectonic influences of the Pyreneo-Cantabrian 

 chain, and therefore belong to a region of exceptional dynamic 

 activity. 



Conclusion. 



This paper has already exceeded the intended length, and yet 

 ■without my having completed the work originally contemplated. 

 It is not altogether an easy task to alternate hydrographical facts 

 with geological theories. Although not holding any particular 

 theory myself, 1 am somewhat inclined to the belief that the larger 

 features of the earth's crust, and particularly the ocean basins, may 

 have been permanent within certain limits. The flanks of these 

 great depressions are more correctly described as slopes rather than 

 as escarpments ; and these slopes are probably due to ancient and 

 deep-seated tectonic causes, active in some places and quiescent 

 for a time in others. The eastern margin of the North Atlantic 

 basin presents, as regards activity of motion in the present day, 

 a marked contrast to the eastern margin of the Pacific, where the 

 mobile condition of the suboceanic slope, off the coasts of South 

 America, is well known. This comparative stability, however, may 

 not always have prevailed. Indeed, we may feel pretty sure that 

 movements have occurred along this line throughout geological time, 

 altogether independent of local eruptions of basalt, etc. 



If I might venture to sum up the results of the views suggested 

 in this paper, they would appear somewhat as follows : — 



1. The true boundary of the North Atlantic basin on this side is 

 not to be sought in the existing coastlines, but in the submerged 

 slope which lies beyond the edge of the submerged platform. 



2. The edge of the submerged platform appears to range from 

 about 80 to 250 fathoms, the most notable deviation from the usual 

 depth occurring in connection with the irregular bulge of submerged 



