338 • Mr. T. M. Reade on Tidal Action as 



Table V. 



Sp.g. 



Hi.. 



ft*. 



v. 



v-1 



Water. 











1000 



1-32924 



1-34393 



1-3249 



3249 



Alcohol. 











07919 



1-3585 



1-3735 



1-3531 



44589 



XLV. Tidal Action as an Agent of Geological Chanqe. 

 By T. Mellard Reade, C.E., F.G.S., F.R.LB.A* 



THE nature of tidal action, as regards its effect on the sea- 

 bottom, seems to be insufficiently understood, if not in 

 many cases actually misapprehended. 



In looking over most of the late works on Geology this fact 

 has been much impressed upon me. Very little influence 

 seems to be attached to the tides as agents of geological 

 change, and then only as surface-currents affecting the coasts 

 and shores. So long ago as 1873, in a paper entitled " Tidal 

 Action as a Geological Cause "f, I attempted to show that the 

 mechanical action of the tides was deep and wide spread, 

 affecting not only the littoral, but the whole bottom of the 

 sea, while the profoundest depths of the ocean are not entirely 

 exempt from tidal movement. 



My present object, while recalling attention to this subject, 

 is to adduce some further facts in support of the important 

 office the tides perform as distributers of material worn from 

 the land, and even in special cases as agents of erosion acting 

 on the sea-bottom. 



The force producing the tidal-wave affects every particle 

 equally, down to the most profound depths of the ocean, while 

 the forces creating wind- waves act only on the surface. A 

 cork floating upon deep water disturbed only by the ordinary 

 waves, revolves (as do also all the surface-particles of water) 

 either in a vertical circle or an ellipse, not very different from 

 one having the longer axis vertical. In the free tide-wave 



* Communicated by the Author. 



t Proceedings of the Geological Society of Liverpool, Session 1873-4. 



