86 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ [ JunC 13, 



the mass of Snowdon from the sea-level of the Caernarvon coast by 

 the Menai Straits. 



The character of the greater part of the Channel area, if laid bare, 

 would be that of extensive plains of sand, surrounded by great zones 

 of gravel and shingle, and presenting much such an admixture and 

 arrangement of materials as we may observe at present over the Bag- 

 shot district of deposits ; whilst along the opening of the Channel 

 there is an obvious configuration of hill and valley, and an amount of 

 inequality equal to that of the most mountainous part of Wales. 



From the summit-levels of the Little Sole Bank to the 200-fathom 

 Hne of soundings on the west, the slopes, though steep in places, are 

 regular. If we deduct the fifty fathoms of water, the remainder will 

 give 900 feet for the elevation of this ridge above the 200-fathom 

 level ; or a range of hills having just the same uniform tabular eleva- 

 tion above such line that the Haldon and Blackdown ranges have 

 above the present sea ; it is about the lower levels of this group that 

 the coarse materials already noticed seem to occur. 



Beyond the 200-fathom hne the outline is irregular, and sinks 

 rapidly to very great depths. This remarkable fact occurs not only 

 at one particular spot, but is continued northwards, and in the con- 

 trary direction has been traced by Captain Vanhello from Cape Finis- 

 terre to the parallel of the Lizard. The investigation of this line seems 

 to have been the special service on which he was employed in 1828 

 and 1829. He states that immediately beyond the 200-fathom hne 

 they often failed to obtain soundings by running out as much as 400 

 fathoms ; and also that the ridge of the Little Sole is placed on the 

 east edge of that 200-fathom line. Of the true nature of such a 

 sudden line of depression we can at present only form conjectures : 

 it may represent lines of old escarpments ; or should lines of sea-clifp 

 have gone down rapidly into deep water, where no mechanical action 

 could modify them, such features would be preserved : hues of faults 

 and upheaval would also present such unequal soundings ; but the 

 outhne is too irregular to represent the termination of the sedimen- 

 tary mass of the present seas ; besides which, we have constant indi- 

 cations of a surface of bare rock. 



Sir H. De la Beche has represented the course of the 100-fathom 

 line round the British islands *, with which that of 200 fathoms has a 

 very close conformity, and he remarks on the agreement which this 

 line presents with that of the strike of the older ranges of this 

 country : such is undoubtedly the case with respect to a portion of 

 this hne ; but if it be suggested by this, that the date of this sub- 

 merged line be the same as that of M. E. de Beaumont's * System of 

 the North of England,' it must be remembered that this 200-fathom 

 hne, if viewed along its entire length, presents no such parallehsm, — 

 that it is continued along the coasts of countries whose ranges present 



* Theoretical Researches, p. 190, In closing these obsen^ations on the con- 

 dition of the bed of the Channel, I gladly acknowledge my obligations to this 

 work ; to it, and Sir C. Lyell's ' Principles,' I must trace the idea I have attempted 

 to work outc 



