30 



One, which was on movable supports, had been sent as a 

 present to the Emperor of Russia, but having been impro- 

 perly directed, was returned. One showed not only the 

 foot prints of an animal, but the passage over its surface of a 

 shell fish or a worm. One exhibited the stride of a gigantic 

 animal, this stride being about nine feet in length. The 

 largest of all had over sixty impressions of feet upon its sur- 

 face. Mica can be seen upon the surface of many of these 

 slabs, and Mr. Bouve thought that this might account for 

 the easy separation of these sandstones into layers. He 

 suggested that in the process of deposition of this rock, 

 mica might have been deposited in greater abundance at 

 certain intervals than at others, and that in these places was 

 the greatest tendency to splitting into layers. 



Prof. Rogers remarked, that some of these specimens had 

 a shining appearance, as if they were once covered with a 

 kind of slime ; finely comminuted mica would give the 

 proper degree of density and plasticity for preserving slight 

 impressions, and he had always been in the habit of looking 

 for the best impressions on glazed surfaces. 



Dr. J. B. S. Jackson observed that Mr. Marsh, who had col- 

 lected the specimens in question, had called his attention to 

 what he called " his books," that is, layers of stone in which 

 the impressions grew less distinct towards the surface, upon 

 which merely a line could be traced. This line had often 

 been a guide to Mr. Marsh to search in lower layers. He 

 supposed the impression to have been made in deep and 

 soft mud, which settled in slowly after the foot was with- 

 drawn. 



Some discussion ensued as to whether certain of these 

 tracks were made by birds or reptiles. 



Mr. Bouve thought they were made by birds. The arti- 

 culations could be counted, and coproliles, which have on 

 analysis been found similar to guano, are found with them. 



