212 THE POPULAR SCIENCE MONTHLY. 



its natural size in the large diagram hanging up here, which I owe to 

 the kindness of my friend Prof. Marsh, with whom I had the oppor- 

 tunity recently of visiting the precise locality in Massachusetts in 

 which these tracks occur. I am, therefore, able to give you my own 

 testimony, if needed, that they accurately represent the state of 



Fig. 1. Tracks of Brontozocm. 



things which we saw. The valley of the Connecticut is classical 

 ground for the geologist. It contains great beds of sandstone, cover- 

 ing many square miles, and which present this peculiarity, that they 

 have evidently formed a part of an ancient sea-shore, or, it may be, 

 lake-shore, and that they have been sufficiently soft for a certain 

 period of time to receive the impressions of whatever animals walked 

 over them, and to preserve them afterward in exactly the same way, 

 as such impressions are at this very moment preserved on the shores 

 of the bay of Fundy and elsewhere. We have there the tracks of 

 some gigantic animal (pointing to the diagram), which walked on its 

 hind-legs. You see the series of marks made alternately by the right 

 foot and by the left foot ; so that from one impression to the other of 

 the three-toed foot on the same side is one stride, and that stride, as 

 we measured it, is six feet nine inches. I leave you, therefore, to 

 form an impression of the magnitude of the creature which must have 

 walked along the ancient shore, and which made these impressions. 



Now, of such impressions there are untold thousands upon these 

 shores. Fifty or sixty different kinds have been discovered, and they 

 cover vast areas. But up to this present time not a bone, not a frag- 

 ment, of any one of the great creatures which certainly made these 

 impressions has been found ; and the only skeleton which has been 

 met with in all these deposits to the present day though they have 

 been carefully hunted over is one fragmentary skeleton of one of 

 the smaller forms. What has become of all these bones ? You see 

 we are not dealing with little creatures, but animals that make a step 

 of six feet nine inches; and their remains must have been left some- 

 where. The probability is, that they have been dissolved away, and 

 absolutely lost. 



I have had occasion to work at scries of fossil remains of which 

 there was nothing whatever except the casts of the bones, the solid 

 material of the bone having been dissolved out by percolating water. 

 It was a chance in this case that the sandstone happened to be of 

 ^uch a constitution as to set, and to allow r the bones to be afterward 

 dissolved out, leaving cavities of the exact shape of the bones. 



