REPTILES ABUNDANT. 55 



replaced by ostraceae of various genera a change from the 

 animals of deep to those of shallow seas. The univalve mol- 

 lusks also indicate a condition of the sea advancing towards 

 that which exists near the present shores. In the new forms 

 of cephalopoda were some marking their advanced character 

 by their non-possession of a shell or stony skeleton. In this 

 case, the existence of the animal is only betrayed by its horny 

 mandible, constituting the fossils called rhynchulites. 



We find in this system further traces, but still obscure and 

 local, of the reptilian class. Before proceeding to speak of 

 them, it is necessary to remark that the ingredients and ar- 

 rangements 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 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 athin layer of fresh 

 sand by the next, and so on, precisely as such circumstances 

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

 surfaces, ripple-marked, present themselves throughout the sub- 

 sequent formations : in those of the New Red, at more than one 

 place in England, they further bear impressions of rain-drops 

 which have fallen upon them the rain, of course, of the incon- 

 ceivably remote age in which the sandstones were formed. In 

 the Greensill sandstone, near Shrewsbury, it has even been 

 possible to tell from what direction the shower came which 

 impressed the sandy surface, the rims of the marks being 

 somewhat raised on one side, exactly as might be expected 

 from a slanting shower falling at this day upon one of our 

 beaches. These facts have the same kind of interest as the 



