180 PALEONTOLOGY. 



lidate the sand layers into a fissile rock : it will split in the 

 way it was formed, and the cleavage will expose the old moulds 

 on one surface and the casts on the other. 



Another condition for fixing the impressions on a sandy 

 shore is the following : — When an extensive level tract is 

 left dry by the retreating tide, as at the estuary of the small 

 rivers entering the Bay of Morecarabe, on the Lancashire coast, 

 those rivers occasionally overflow the sands at low-water, 

 and deposit in the footprints made previous to such overflow 

 the fine mud which sudden heavy rains have brought down 

 from the surrounding hills. Again, those sudden " freshets," 

 as they are locally called, sometimes as quickly subside, and 

 a thin layer of argillaceous mud is left on the sand. This 

 layer readily receives the footprints of the many birds that 

 course over the flat expanse, and may become hard enough to 

 retain them when the- tide returns and deposits in such foot- 

 prints a layer .of the .fine sand which the rising waters hold 

 in suspension. - , ^ 



The best-defined footprints in the new red sandstone 

 quarries at Stourton, on the Cheshire coast, are found where 

 strata of sandstone are separated by a thin layer of argil- 

 laceous stone, which, when exposed, soon breaks up and 

 crumbles away. This layer has, however, received the im- 

 pressions when it was plastic, and the superincumbent deposit 

 of sandstone retains those impressions in relief upon its under 

 surface. The conditions producing an interposition of a thin 

 layer of claystone between thicker beds of sandstone, which 

 the writer has witnessed in the Bay of Morecambe, explain 

 the formation and the preservation of the best " ichnites" of 

 the labyrinthodont and other reptiles in the new red sandstone 

 of Stourton. 



There is a third condition under which impressions, and 

 casts of impressions, on a sandy beach may be preserved. On 

 a dry windy day clouds of fine sand are drifted along the sur- 



