178 PALEONTOLOGY. 



tides melted in its swift passage through the earth. The 

 hailstone, the ripple wave, the rain-drop, even the wind that 

 bore the drops along and drove them slanting on the sand, 

 have been registered in casts of the cavities which they 

 originally made on the soft sea-beach ; and the evidence of 

 these and other meteoric actions, as sun-cracks and frost- 

 marks, so written on imperishable stone, have come down to 

 us from times incalculably remote. Every form of animal 

 that, writhing, crawling, walking, running, hopping, or leap- 

 ing, could leave a track, depression, or foot-print, behind it, 

 might thereby leave similar lasting evidence of its existence, 

 and also to some extent of its nature. 



The interpretation of such evidences of ancient life has 

 much exercised the sagacity of naturalists since Dr. Duncan, 

 in 1 828, first inferred the existence of tortoises at the period 

 of the deposition of certain sandstones in Dumfriesshire, from 

 the impressions left on those sandstones, and the casts after- 

 wards formed in those impressions. The interpreting faculty 

 has been still more racked by similar evidences of more extra- 

 ordinary footprints (fig. 83), probably of large batrachian 

 reptiles, first noticed in 1834 at Hildberghausen in Saxony, in 

 sandstones of the same geological age as those in Scotland. 



The vast number and variety of such impressions, due 

 either to physical or meteoric forces, to dead organic bodies, 

 parts or products, or to the transitory actions of living beings, 

 have at length raised up a distinct branch of palseontological 

 research, to w T hich the term " Ichnology" has been given. 



In this class of evidences the impressions called " protich- 

 nites"* (fig. 82), left upon the "Potsdam sandstones "t of the 

 older Silurian age in Canada, are the most ancient ; but the 



* See Owen, " Description of the Impressions and Footprints of the Prot- 

 ichnites from the Potsdam Sandstone of Canada," Quarterly Journal of the 

 Geological Society, 1852, p. 214. 



f Logan, ibid. p. 2. 



