568 MR. PALMER ON THE MOTIONS OP SHINGLE BEACHES. 



observations are chiefly directed to the particular manner in which the motions are 

 produced. 



From a general view of the effects that I have noticed, it appears that the actions 

 of the sea upon the loose pebbles are of three kinds : the first heaps up, or accumu- 

 lates the pebbles against the shore ; the second disturbs, or breaks down the accumu- 

 lations previously made ; and the third removes, or carries forward the pebbles in a 

 horizontal direction. 



For convenience I propose to distinguish these by the following terms, viz. the first, 

 the accumulative action ; the second, the destructive action ; the third, the progres- 

 sive action. 



All the consequences resulting from these various actions are exclusively referrible 

 to two causes. The one is to the current, or the motion of the general body of the 

 water in the ebbing and flowing of the tides ; the other to the waves, or that undu- 

 lating motion given to the water by the action of the winds upon it ; and it is of con- 

 siderable importance to the present inquiry that the effects resulting from each spe- 

 cific cause be separately considered. 



The motion of the shingles along the shore is commonly attributed to the currents, 

 the action of the waves being considered only as a disturbing force. That such a 

 notion is erroneous will, I apprehend, presently appear ; although I have to regret 

 that I have not had the opportunity of obtaining such satisfactory information re- 

 lating to the velocities of the currents in the channel as would have enabled me to 

 include every form of argument upon the subject. The absence of such information 

 has also prevented me from deciding satisfactorily as to the sources from whence the 

 whole body of shingle is derived, which, although not necessary for the practical 

 purposes I have in view, would have given more interest to the subject, and would 

 have rendered the elucidation more complete. I must, therefore, for the present, be 

 content to pursue the motions of the beach after it is found lying along or near the 

 shore ; observing only that the materials of which it is composed are those of the 

 various strata in the vicinity of the coasts, together with the ordinary sea sand, and 

 such small particles as may have been brought to the shore by the floods of the 

 various rivers. 



That the current is not the force which moves the pebbles along the coast, will 

 appear from the following reasons : 



1st. If it were so, the direction of the motion of the pebbles would be determined 

 by that of the currents ; but while the direction of the currents will vary with the 

 changes of the tides, we find that the direction of the pebbles may remain unaltered ; 

 and also that the motion of the pebbles is continued where no current exists. 



2nd. Although the velocities of the currents may not have been ascertained with 

 precision, yet it is known that the velocities generally along this coast, which can 

 possibly act on the shingles, are not sufficient to give motion to pebbles of every 

 dimension, which are in fact carried forward. 



