146 



PROF. EDWARD HULL^ LL.D., r.R.S., F.G.S., ON 



continued into what is now the air; these vanished masses 

 having been planed off the surface by the waves of an ocean 

 which once swept over the existing land when at a lower level 

 than at present, leaving an inclined plane surface known as " a 

 plain of marine denudation."* This term was first proposed by 

 its author to the surface of the Silurian district of Cardigan- 

 shire, which, though consisting of alternating hills and valleys 

 formed of inclined Silurian slates and grits like those of 

 Cornwall, terminate upwards along an imaginary plain surface, 

 sloping gently from the interior to die sea-coast. (Fig. 3, p. 147.) 

 To this subject we may v/ell give our attention for a short time, 

 as it is one of great physical interest. 



Plains of Marine Demtdatioii. — Everywhere in the south and 

 west of England and Wales we are confronted by plains of 

 marine denudation, a term first employed by Sir Andrew 

 Eamsay.f Let me illustrate what I mean by this term. 

 Supposing the P3ritish Isles and Western Europe to be elevated 

 froni 100 to 200 fathoms above their present level as deter- 

 mined by tlie surface of the ocean, they would be found to have 

 a fringe of varying breadth consisting of a gradually sloping 

 surface bounded inland by the coast cliffs and breaking off in 

 the direction of the ocean, by an abrupt declivity (or escarp- 

 ment) leading down to the abyssal regions. This gently 

 sloping fringe, sometimes 20 to 100 miles in breadth, would, 

 therefore, constitute a plain, and as it was formed by the ocean 

 waves and currents, ever wearing back the coast, breaking 

 down the rocks and reducing the surface of the land to that of 

 the surface of the ocean, it would constitute a plain of marine 

 denudation.^ This plain would at intervals be crossed by 

 river-valleys descending from the interior lands into the 

 abyssal ocean below. Such plains are also represented on the 

 land, wherever the land has been, at whatever period, below the 



The name proposed by the late Sir A. C. Eamsay in his work, The 

 Physical Geology and Geography of Great Britain^ 5 Edit., p. 497 (1875). 



t Ihid.^ p. 497. This term in the abstract might be written "planes of 

 marine denudation"; but in the concrete as applied to special features 

 of the landscape the term appears the more correct. 



% The process of formation of this plain, constituting as it does the 

 land margin of the Great Continental Platform, is admirably illustrated 

 in the picture of Widemouth Bay, Bude, in Clornwall, given by Lord 

 Avebury in his Scenery of England (p. 126), where the highly tilted and 

 contorted strata of Devonian age, as seen in the coast cliffs, are planed 

 down by wave action to a general surface sloping gently seaward, and 

 laid bare at ebb tide. 



