IMPRESSIONS OF THE PAST 41 



tween the deposits being so short that the 

 tracks of the big Dinosaurs extend through 

 several sheets of stone ; while again there was a 

 period of drouth when the shore became so dry 

 and firm as to retain but a single shallow im- 

 pression. 



Something of the wealth of animal life that 

 roamed about this estuary may be gathered 

 from the number of different footprints re- 

 corded on the sands, and these are so many and 

 so varied that Professor Hitchcock in two ex- 

 tensive reports enumerated over 150 species, 

 representing various groups of animals. One 

 little point must, however, be borne in mind, 

 that mere size is no sure indication of differ- 

 ences in dealing with reptiles, for these long- 

 lived creatures grow almost continuously 

 throughout life, so that one animal even may 

 have left his footprints over and over in as- 

 sorted sizes from one end of the valley to the 

 other. 



The slab shown in Fig. 7 is a remarkably 

 fine example of these Connecticut River foot- 

 prints; it shows in relief forty-eight tracks of 

 the animal called Brontozoum sillimanium and 



