KiNAHAX — On Sea-beaches. 191 



XXXIII. — Sea-beaches, especiaxlt those of "Wexfokd and "Wick- 

 low. By Q. H. Kinahan. (With Plates 4, 5, 6, 7.) 



[Eead January 27, 1879.] 



The travelling of sea-beaches is a very interesting subject to the geo- 

 logist, but it is one most important to the engineer, as it affects so 

 strongly the questions of the proper positions and construction of 

 harbours, piers, and groynes. During the time I have been engaged 

 on the Greological Survey of Ireland (over twenty years) I have had, 

 when stationed in maritime districts, favourable opportunities of ob- 

 serving the sea-beaches. This has been specially so during the last 

 six years, while I have been engaged in examining the counties of 

 Wicklow and "Wexford, and in those years the observations made 

 were both numerous and minute. 



From the Papers read before the different Scientific Societies it 

 would appear that two of the principal points of controversy as 

 regards this subject are : — Whether are the wind waves or the tidal 

 currents the principal moving agents in the shifting of the beaches ? 

 and — Can large stones be carried by somewhat ordinary ocean currents 

 in deep water ? To these subjects I have also paid special attention. 



I propose laying before the Academy the resrdts of my obser- 

 vations, which relate to : — 



I. The travelling of beaches due to the tidal currents. 

 II. The effects of the wind waves. 



III. Carriage of stones in deep water. 



IV. The effects of the travelling of beaches on the harbours 



and piers between Hook Point (Admiralty Chart, Ireland, 

 sheet xiv.) and Dalkey Island (Admiralty Chart, sheet 

 xvi.) ; concluding with 

 Y. A discussion of the groynes on the coast-line between Hook 

 Point and Dalkey Island. 



I. Travelling of Reaches due to the Tidal Currents. 



This Paper will more especially refer to the observations made on 

 the coast-line of south-east Ireland included in the Admiralty Charts, 

 Ireland, sheets xiv., xv., and xvi.^ On the accompanying map 

 (Plate 4) the principal on-shore flow-tide currents have been indi- 

 cated ; those going with the course of the tide, the counter-currents 

 (counter-tides), and the half-counter-tides. 



As pointed out in Haughton's Manual of Tides and Tidal Cur- 



1 Sheet XV. is on the scale of two inches to the mile. The chart on the scale of 

 one inch cannot now be procured ; 'while the other charts, on the larger scale, have- 

 not as yet been published. 



