318 Prof. Hitchcock on Ichnolithology, or Fossil Footmarks. 



lY, Order Apodichnites, or footless tracks. 



' ^ ' , 1 In Gloucestershire and Flintshire, 



2. By mollusks. > 



o r> rj I England. 



3. By annelidous worms. J 



Two or three remarks may perhaps be needed concerning the 

 preceding tabulation of the footmarks, especially those of the 

 valley of the Connecticut. The number of species may seem 

 to some so large as to excite the suspicion that the characters on 

 which they are founded are merely imaginary. But it should 

 be recollected that these tracks have been obtained from a region 

 eighty miles long and several miles broad, from more than six- 

 teen quarries, and that they were not produced by birds that were 

 cotemporaries, but which existed through a long series of centu- 

 ries. Thus, at Turner's Falls we find tracks on layers dipping 

 40°, and separated from each other not less than eighty rods on 

 the surface, and of course forty rods in perpendicular thickness ; 

 and how long it would take to deposite layers of fine sandstone 

 and shale forty rods thick, let those familiar with the rules of ge- 

 ological arithmetic calculate. Taking the rate at which lakes fill 

 up in Scotland as the basis of the estimate, it would require more 

 than one hundred and thirty thousand years ; and admitting a 

 much more rapid rate of deposition, we should have time enough 

 to expect a great variety of animals to have trod upon the difierent 

 layers. I may have founded some species upon uncertain charac- 

 ters, and it would be strange if better specimens should not remove 



