36 0N THli REVOLUTIONS OK 



if the invention of man does not teach him how to fix hy introducing 

 herbage suited to the soil, progress slowly, hut with certainty, towards 

 the interior of the country, and then overwhelm fields and dwellings ; 

 because the same wind which conveys the sand of the beach on to the 

 down casts that of the summit of the down still farther inland. But if 

 the nature of the sand and that of the water it absorbs, are such as 

 form a durable cement, the shells and bones cast on the shore will be- 

 come incrusted with it ; woods, trunks of trees, and plants which grow 

 near the sea-side, will become enveloped in these accumulations ; and 

 thus will be formed those solid downs such as are to be met with on 

 the coasts of New Holland. We can have a clear idea of them from 

 the description given by Peron*, 



Steep Shores. 



When, on the contrary, the coast is lofty, the sea, which can deposit 

 nothing, is perpetually destroying ; its waves wear away the bank, 

 and destroys the summit, because the higher parts, being left without 

 foundation, are incessantly falling away into the sea, where they are 

 tossed about by the waves until the softer and looser particles are lost. 

 The harder portions, by dint of continued friction, form those round 

 pebbles, or that accumulated strand which serves to strengthen the 

 base of the steeps. 



Such is the action of the waters on terra firma, which consists only 

 in small levellings, and those not indefinite. The falling materials of 

 the mountain tops into the vallies ; their particles, those of the hills 

 and plains, conveyed to the sea ; the alluvial deposites extending the 

 coasts at the expense of the heights, — are the limited effects which 

 vegetation has in some degree put a boundary to ; which suppose, be- 

 side the pre-existence of mountains, valleys, in short, of all the ine- 

 qualities of the globe, and which consequently could not themselves 

 have produced those inequalities. The downs are a still more limited 

 phenomenon, both in height and horizontal extent ; they have no re- 

 lation to those enormous masses into the origin of which geology seeks 

 to penetrate. 



As to the operation of the waves in their own element, although we 

 cannot accurately ascertain it, yet we can to a certain extent point out 

 its effects. 



Deposites under the Waters. 

 Lakes, ponds, marshes, and sea-ports into which streams flow, par- 

 ticularly when issuing from neighbouring and rugged hills, deposit at 



* In his " Voyage aux Terrcs Australes." 



