Tracks of Animals in the Forest Marble. 539 



measured, perhaps, in miles ; the corresponding beds in neigh- 

 bouring quarries being found to have the same configuration. 



It is to be seen chiefly in the very fissile laminae, but not 

 unfrequently on the surface of slabs eight or ten inches in 

 thickness. It affects indifferently those which contain a large 

 proportion of clay, those which are highly calcareous and crys- 

 talline, and others in which sand and oolitic grains, or minute 

 fragments of shells predominate. The only circumstance, as 

 it appears to me, which the ripple marked beds possess in 

 common, is their separation from the neighbouring strata, by 

 more or less thin seams of clay , moulded on the irregular sur- 

 face below, and by which the preservation of that surface, in 

 complete integrity, exactly as it was figured by the waves of 

 the ocean, at an incalculable distance of time, seems to be 

 simply and naturally accounted for. 



The ripple-marks are always on the upper face of the bed ; 

 but where the seams of clay are very thin, the alternating 

 limestone laminae have taken the impression of the uneven 

 surface on which they were deposited, and thus present an im- 

 perfect ripple on their lower face also. In this case, however, 

 the undulations of the upper and lower surfaces do not corre- 

 spond, but often cross and run counter to one another : occa- 

 sionally, too, a double system of wrinkles may be seen on the 

 same surface ; the undulatory movements of the water, by 

 which they were produced, having shifted their direction (per- 

 haps through a change of wind) during the period of the de- 

 position. 



I am not acquainted with any published explanation of the 

 cause of the rippled surface which, at low tide, may be seen 

 extending over many square miles of sand or mud along the 

 Devonshire, Lancashire, and many other of our flat and shallow 

 shores. That it is disturbed and renewed again, partially or 

 entirely, by every fresh tide, is known to all who have remarked 

 the constant changes which it undergoes, and the obliteration 

 of all marks made in the sand at one low tide, before the next 

 ebb. There can be little doubt that it is produced by the 

 oscillatory motion of the lower stratum of water in contact with 

 the sandy or muddy bottom, as communicated to it from the 



