146 WAVES OF THE SEA 



keep very fine mud moving about until it has an 

 opportunity of subsiding over the edge of the conti- 

 nental shelf in the absence, that is to say, of 

 chemical or other coagulation of the fine particles 

 into clots or lumps. 



The Action of Waves to Drive Shingle Shorewards 



It is matter of common experience that the stones 

 brought on to the sea -shore (e.g., by the wasting 

 of gravel cliffs or by the wash of stone -carry ing 

 torrents), though swept along the coast and thus 

 distributed, are to a great extent rejected by the 

 sea and piled up in a bank, so that some of the 

 stones are only reached again by the largest waves 

 at the times of high water of the greatest tides. 

 Classifying the detritus brought to the sea -shore 

 into three sorts, viz., shingle, sand, and mud, we 

 may say that those parts of the sea bottom which 

 are subject to wave disturbance afford no abiding 

 place for either the first or the last. 



We have seen how the mud travels on the whole 

 in a direction contrary to that of the swell, which, 

 having " felt the bottom," is advancing shore wards. 



I now put forward a theory which I think shows 

 that the oscillations of the bottom water where 

 agitated by progressive waves has a proper action 

 of its own to heave forward /.., in the direction 



