LAND PLANTS AND ANIMALS. 55 



(Stagonolepis), &c. But grave doubts are now entertained re- 

 garding the age of the rock, which most probably walking 

 by palaeontological guidance will prove to be much more 

 recent.] 



It here becomes necessary to remark that the ingredients 

 and arrangements of rocks, with fossil remains, do not form 

 the sole materials of the history compiled by the geologist. 

 He is equally contented when he can find an intelligible fact 

 told by what may be called a writing of nature upon these 

 stone tablets. So low as the bottom of the carboniferous 



FIG. 31. 



Slab of ripple-marked sandstone. 



system, slabs are found marked over a great extent of surface 

 with that peculiar corrugation or wrinkling, which the receding 

 tide leaves upon a sandy beach when the sea is but slightly 

 agitated ; and not only are these ripple marks, as they are 

 called, found on the surfaces, but casts of them appear on the 

 under sides of slabs lying above. The phenomena suggest 

 the time when the sand ultimately formed into these stone slabs 

 was part of the beach of a sea of the carbonigenous era ; when, 

 left wavy by one tide, it was covered over with a thin layer of 

 fresh sand by the next, and so on, precisely as such circum- 

 stances might be expected to take place at the present day. 

 Sandstone surfaces, ripple-marked, present themselves through- 

 out the subsequent formations : in those of the New Red, at 



