178 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



and they persist — firstly, because the original supply was great ; 

 secondly, because for some time after their formation the sea was con- 

 stantly deepening over them ; and lastly, those only remain which 

 have formed from material capable of resisting decomposition. 



APPENDIX I. 



M. Delesse on the English Channel. Translated extract.^ 



" La Manclie, whicli washes the whole north-west of France, is a shallow 

 sea, its mean depth being no more than 45 metres. Its basin shoals near the 

 coasts of France and England, and also toward the Pas-de-Calais, while 

 deepening toward the Atlantic. 



"We would direct attention to the submarine terraces which border the coasts 

 as among the princi})al features of the orography of la Manclie. Outside 

 these terraces somewhat numerous banks occur, especially toward the Pas-de- 

 Calais, as, for instance, the Bassure, the Vergoyer, and the Golhart, which lie 

 near and parallel Avith the French coast. 



"ISTote should be made of the central deep which stretches from off the 

 county of Sussex to Finistere. Near cap de la Hague, at the western extreme 

 of Gotentin, it twists and presents irregular ramifications. 



" In breadth but slight, in depth it much exceeds the rest of la Manchet 

 reaching even, at the west of cap de la Hague, to over 160 metres. This 

 central deep corresponds to a submarine valley, and that it has not been 

 scoured out by the currents of la Manclie its characteristics clearly show. It 

 is formed, on the contrary, by a deep cleavage, having a general direction of 

 E.jST.E., and, although very narrow, not yet filled by recent deposits. 



" Since la Manclie is swept by strong currents, it should follow that deposits 

 are not universally received on its bed, which, on the contrary, should 

 frequently be formed of rocks {I'oches pierreuses) of earlier than the present 

 period; and this, in fact, the soundings show, while these rocks occupy an 

 even greater proportional area of the bed than in other seas. 



" In the first place, they cover large areas in the western part of la Manche ; 

 they border Brittany and Cotentin, which they join to Jersey and the other 

 Channel Islands ; and further they unite Brittany to Cornwall, and Cotentin 

 to the south of England. Cutting out on very irregular boundaries, not only 

 do they spread along the coasts, but pass completely across 7a Manclie, 

 extending even to the deepest parts of its basin and the mid-course of its 

 valley. 



"These rocks are certainly very varied; between Brittany, Cotentin, and 

 Cornwall and Devonshire, they are, however, either granites, or belong to the 

 1 Lithologie des Mers de France, etc., p.p. 308-9. 



