A, Geikle — On Denudation now in Progress. 253 



or that the rate of denudation (and consequently of deposition) must 

 have been in past time infinitely slower than at the present day. 

 The former half of the alternative will be at once rejected ; the latter 

 goes in the face of all received geological belief. 



In accordance with the views now exjircssed, existing lakes as a 

 rule must be of comparatively modern origin. We see that the 

 streams which enter them push j^early increasing deltas into the 

 water. The rate at which the deltas grow shows that they cannot, 

 in a geological sense, be very old. If the delta of the Khone has 

 crept a mile and a half into the lake of Geneva during eight cen- 

 turies, a thousand years must represent no insignificant fraction of 

 the interval since the river began to push its detritus into the lake. 

 Had the lake basin, therefore, been of ancient origin, it must neces- 

 sarily have been long ago filled up with sediment ; and, once in that 

 condition, no power of running water could re-excavate it so as to 

 turn it into a lake again. If the immense mass of lakes scattered 

 over the temperate and northern parts of our hemisphere be due in 

 any large measure to underground forces, there must have been in 

 recent geological times an amount of dislocation, upheaval, and de- 

 pression, of which there is no other evidence, and which indeed is 

 directly contradicted by the actual facts. "We are driven, therefore, 

 to seek some explanation which will account for these rock basins 

 on the admission that they are of recent date, and cannot be due to 

 underground agency. The theory of Professor Ramsay — that they 

 were scooped out by the ice of the Glacial period — harmonizes these 

 postulates, and furnishes a most important element in the elucidation 

 of the history of the earth's surface. 



II. — The detritus wasted from the land is carried away not only 

 by streams, but in part also by the waves and currents of the sea. 

 Yet if we consider the abrasion due directly to marine action, we shall 

 be led to perceive that its extent is comparatively small. In what 

 is called marine denudation, the part played by the sea is rather that 

 of removing what has been loosened and decomposed by atmospheric 

 agents than that of eroding the land by its own proper action. 

 Indeed, when a broad view of the whole subject is taken, the amount 

 of denudation which can be traced to the direct effects of the sea 

 alone is seen to be altogether insignificant. Yet even if we grant 

 to the action of the waves and tides all that is usually included 

 under marine denudation, the sum total of waste along the sea- 

 margin of the land is still trifling compared with that effected by 

 the meteoric agents upon the interior. Islanders, as we are, familiar 

 from infancy with the fury of the breakers which beat along our 

 coast-line and strew it with wrecks, we are apt to attribute to the 

 ocean too great a share in the work of wearing down the land. 

 Even in an island like Britain the extent of surface exposed to the 

 power of the waves is very small indeed when contrasted with that 

 which is under the influence of atmospheric waste. And, of course, 

 in the case of the continents the discrepancy is infinitely greater. 

 In the general degradation of the land this is an advantage in favour 

 of tte subaerial agents, which would not be counterbalanced, unless 



