336 



accounted for, by movements of elevation and depression acting upon 

 the bed of the sea with unequal measures of intensity , raising up shells, 

 gravel, and boulders which were accumulated at the same period, to the 

 respective levels which they now occupy, doubtless producing many of 

 the cracks and fissures with which the solid strata are replete, and 

 leaving denuded valleys between the points so elevated. 



