ANCIENT RIPPLE-MARKS. 329 



bays, deltas, lakes, and estuaries, in comparatively 

 shallow water. In many parts of the Wealden 

 formation these appearances are very striking ; 

 especially in the vicinity of Horsham,* and in the 

 quarries in Tilgate Forest in Sussex, j- The slabs 

 of limestone, clay, and sandstone, exposed in 

 recent falls of the cliffs along the southern shores 

 of the Island, are frequently covered with ripple- 

 marks. 



Every one must have noticed when walking by 

 the side of a river at low water, or on the sands of 

 the seashore, that if the water has been agitated by 

 the wind, the surface of the mud or sand is fur- 

 rowed more or less deeply by the rippling of the 

 waves ; the markings presenting various appear- 

 ances according to the force and direction of the 

 wind and currents. The undulations on the sur- 

 face of the sandstone have arisen from similar 

 operations. In many instances the stone is so 

 rough as to be employed in stable-yards, where an 

 uneven surface is required to prevent horses from 

 slipping as they pass over. Sometimes the fur- 



* These were first noticed by Mr. Lyell in 1822, and described in a letter 

 addressed to the author. 



t It is singular that although Professor Playfair mentions the cause of this 

 appearance as undoubted, yet so little attention or credit was given to the 

 statement, that my description of the phenomenon was received with much 

 hesitation. 



