88 LECTUKES ON EVOLUTION in 



sured it, is six feet nine inches. I leave you, 

 therefore, to form an impression of the magni- 

 tude of the creature which, as it walked along 

 the ancient shore, made these impressions. 



Of such impressions there are untold thousands 

 upon these sandstones. Fifty or sixty different 

 kinds have been discovered, and they cover vast 

 areas. But, up to this present time, not a bone, 

 not a fragment, of any one of the animals which 

 left these great footmarks has been found ; in 

 fact, the only animal remains which have been 

 met with in all these deposits, from the time of 

 their discovery to the present day though they 

 have been carefully hunted over is a fragmentary 

 skeleton of one of the smaller forms. What has 

 become of the bones of all these animals ? You 

 see we are not dealing with little creatures, but 

 with animals that make a step of six feet nine 

 inches ; and their remains must have been left 

 somewhere. The probability is, that they have 

 been dissolved away, and completely lost. 



I have had occasion to work out the nature of 

 fossil remains, of which there was nothing left 

 except casts of the bones, the solid material of the 

 skeleton having been dissolved out by percolating 

 water. It was a chance, in this case, that the 

 sandstone happened to be of such a constitution 

 as to set, and to allow the bones to be afterward 

 dissolved out, leaving cavities of the exact shape 

 of the bones. Had that constitution been other 



