CHAP. XIV. IN BRITISH PHYSICAL GEOGRAPHY. 277 



It appears, from soundings made during various Admiralty 

 surveys, that the gained land thus brought above the level of 

 the sea, instead of presenting a system of hills and valleys 

 corresponding with those usually characterizing the interior 

 of most of our island, would foi'm a nearly level terrace, or 

 gently inclined plane, sloping outwards like those terraces of 

 denudation and deposition which I have elsewhere described 

 as occurring on the coasts of Sicily and the Morea.* 



It seems that, during former and perhaps repeated oscil- 

 lations of level undergone by the British Isles, the sea has 

 had time to cut back the cliffs for miles in many places, 

 while in others the detritus derived from wasting cliffs 

 drifted along the shoi*es, together with the sediment brought 

 down by rivers and swept by currents into submarine valleys, 

 has exerted a levelling power, filling up such depressions aa 

 may have pre-existed. Owing to this twofold action, few 

 marked inequalities of level have been left on the sea-bottom, 

 the '' silver-pits" off the mouth of the Humber offering a 

 rare exception to the general rule, and even there the narrow 

 depression is less than 300 feet in depth. 



Beyond the 100 fathom line, the submarine slope surround- 

 ing the British coast is so much steeper that a second eleva- 

 tion of equal amount (or of 600 feet) would add but slightly 

 to the area of gained land; in other words, the 100 and 200 

 fathom lines run very near each other.f 



The naturalist would have been entitled to assume the 

 former union, within the post-pliocene period, of all the British 

 Isles with each other and with the continent, as expressed in 

 the map, fig. 41, even if there had been no geological fiicts in 

 favor of such a junction. For in no other way would he be 

 able to account for the identity of the fauna and flora found 

 throughout these lands. Had they been separated ever since 



® Manual of Geology, p. 74. 



f De la Beche, Geological Researches, p. 191. 



