THE STORY THE SEA TOLD 159 



mud or sand was allowed to settle and form 

 above any mark which had been made. But 

 in the deposits of sandstone and other rocks, 

 which were once the shores of the sea, we find 

 innumerable numbers of the little, wavy lines 

 which mark the lapping wave-edges while the 

 little half-round holes made by falling rain- 

 drops are very common. Here and there we 

 may trace the irregular track of a tiny snail or 

 mollusc, while in some places the rocks, when 

 split apart, reveal hundreds of the perfectly 

 preserved skeletons of fish. Sometimes the 

 slabs of stone show still more wonderful and 

 remarkable records and when the layers are 

 separated they disclose great three-toed foot- 

 prints; the tracks of huge cumbersome crea- 

 tures which lumbered across the sand-beaches 

 and mud-flats in the prehistoric days and left 

 their sharply-marked trails upon the smooth 

 surface. At times these tracks are single and 

 apparently made by one animal, while at other 

 times they cross and recross and there are 

 tracks of various sizes showing that not one 

 but many animals wandered over the flats be- 

 tween tides. These things all prove that these 



