!2o4 A. GelJde — On Denudation noiv in Progress, 



tlie rate of waste by the sea were many thousands or millions of 

 times greater than that of rains, frosts, and streams. But no such 

 compensation exists. Let us suppose that the sea eats away a conti- 

 nent at the rate of ten feet in a century — an estimate which probably 

 attributes to the waves a very much higher rate of erosion than can 

 as the average be claimed for them, — then a slice of about a mile in 

 breadth will require about 52,800 years for its demolition, ten miles 

 will be eaten away in 528,000 years, one hundred miles in 5,280,000 

 years. But we have already seen that on a moderate computation 

 such a continent as Europe will, at the present rate of subaerial 

 waste, be worn away in about 4,000,000 years. Hence, before the 

 sea could pare off more than a mere marginal strip of land between 

 70 and 80 miles in breadth, the whole land would be washed into 

 the ocean by atmospheric denudation.^ 



If therefore the elements have acted upon the surface of the land 

 in past time with any approach to the proportions in which they are 

 acting now, it is clear that the sea can have played but a secondary 

 part in modelling the outlines of a continent. It may be objected, 

 to this conclusion, that the traces of wide level tracts, known as 

 plains of marine denudation, so commonly to be met with over the 

 earth's surface, can only be attributed to sea-action, and prove the 

 sea to have had no small share in the general task of planing down 

 the land. These plains are, indeed, in all probability, referable to 

 the action of the sea ; but if we reflect on the tendency of atmo- 

 spheric waste, we must perceive that such plains are the natural 

 and necessary result of that waste. In short, a " plain of marine 

 denudation " is the sea-level, to which a mass of land has been 

 reduced by rains, ice, and streams, — the line below which further 

 degradation became impossible, because the land was thereafter 

 protected by being covered by the sea. Undoubtedly the last 

 touches in the long process of sculpturing were given by the waves 

 and currents ; yet in the past history of our planet the influence of 

 the ocean has been far more conservative than destructive. Beneath 

 the reach of the waves the surface of the submerged land has 

 escaped the demolition which sooner or later overtakes all that rises 

 above them, and there too have been accumulating the sedimentary 

 materials out of which the existing continents have been framed. 



n. — The Suffolk Bone-bed and the Diestien ob Black Crag 



IN England. 



By E. PtAY Lankester, Junior Student of Christ Church, Oxford. 



IN the following pages, I am anxious briefly to make known 

 certain new facts bearing on the history of the Crags which 

 I have recently ascertained, and also to make some observations on 

 papers lately published relating to those beds. 



^ The action of meteoric agents and of the sea is independent of subterranean 

 movements, and must go on whether a land is upheaved or depressed. These move- 

 ments will in some cases favour subaerial denudation, in others marine denudation, 

 as shewn in the paper of wliich the above is an abstract. But in taking a generalized 

 view of the subject their influence may be disregarded. 



