§ 8. RIPPLE MARKS OX SANDSTONE. 373 



that the stone is employed in stable-yards, where an 

 uneven floor is required, to prevent the feet of animals from 

 slipping in passing over. It sometimes happens that when 

 a large area of a quarry is cleared from the soil which 

 covers it, a most interesting appearance is presented, the 

 whole surface being rippled over like the strand on the 

 sea-shore ; and the spectator is struck with the conviction, 

 that he is standing on the sands of some ancient delta, or 

 estuary, now turned into stone. Sometimes the furrows 

 are deep, showing that the water was much agitated, and 

 the ripple strong ; in other instances the undulations are 

 gentle, and intersected by cross ripples, proving a change 

 in the direction of the waves. Some slabs are covered by 

 slightly elevated, longitudinal ridges of sand, made up of 

 gentle risings, disposed in a crescent-like manner ; these 

 have been produced by the rills which flowed back into 

 the river, at low water. In other examples, the surface 

 is marked by angular ridges irregularly crossing each 

 other, like the nssures in septaria ; these have obviously 

 been caused by deposition into crevices produced in sand 

 or mud by desiccation. Many slabs of stone, the smooth, 

 as well as the furrowed varieties, are covered with small, 

 subcylindrical markings, which are the trails formed by 

 vermes, or mollusca ; but I have searched in vain for the 

 foot-marks of turtles or other reptiles, whose bones are so 

 abundant in these strata. The frequent occurrence of 

 impressions of the feet of animals on the rippled sandstone 

 of other formations, renders it probable, that sooner or later, 

 the tracks of some of the oviparous quadrupeds of the 

 Wealden, will be discovered on the slabs of Tilgate stone. 

 The deepest furrows have generally a slight coating of 

 bluish clay, charged with minute portions of lignite, and 

 other vegetable matter ; an appearance probably caused by 

 the streams from the shore, that flowed over and coated the 

 rippled sand. The phenomena here noticed afford an 



