70 SUBSIDENCE IN THE CREATION OF CLIFFS. 



The answer to these questions must of course always 

 remain more or less a matter of conjecture. Never- 

 theless, if we might venture to hazard an opinion, we 

 should decidedly be inclined to ascribe the existence 

 of these cliffs to subsidence. In "The Undercliff," 

 for instance, there are numerous evidences which 

 point to the action of extensive land-slides some of 

 which are matters of historical record. 



We can come to no other conclusion that that the 

 great ranges of bluffs in North America were formed 

 in a precisely similar manner, by an extensive land- 

 slide upon a gigantic scale, possibly consequent upon 

 the softening down of substrata by the infiltration of 

 subterranean waters, or more probably still by the 

 withdrawal of the support afforded by the waters of 

 an ancient sea; of whose former presence the marine 

 shells, etc., found embedded in the stratified rocks, 

 afford, as geologists unanimously admit, indisputable 

 evidence. And as the experience of engineering works 

 shows, the lowering of the waters of a lake or other 

 inland reservoir, by drainage, etc., will almost always 

 produce upon the banks superficial land-slides, which 

 will often exactly represent in miniature the great earth 

 movements of which we have here spoken. In such 

 cases, there can be no doubt as to the exciting cause 

 the support afforded by the mechanical pressure of 

 the water being gone the bank is no longer able to 

 stand; a fissure forms in its surface, the bank 

 cracks away from its former position, and slips down 

 to a lower level, so far as the force of gravity 

 admits of it leaving a miniature cliff standing be- 

 hind it. 



These land-slides are however merely one of the 



