72 PETRIFACTIONS AXD THEIR TEACHINGS. CHAP. I. 



tion of impressions of the feet of animals, walking be- 

 tween high and" low water. In the prolongation of the same 

 beds in the valley of the Connecticut, there have been found, 

 according to Professor Hitchcock, the footprints of no less 

 than thirty-two species of bipeds and twelve of quadrupeds. 

 They have" been observed in more than twenty localities, which 

 are scattered over an area of nearly eighty miles from north to 

 south in the States of Massachusetts and Connecticut. After 

 visiting several of these places, I entertained no doubt that 

 the sand and mud were deposited on an area which was slowly 

 subsiding all the while, so that at some points a thickness of 

 more than 1,000 feet of superimposed strata had accumulated 

 in very shallow water, the footprints being repeated at vari- 

 ous intervals on the surface of the mud throughout the entire 

 series of superimposed beds. 



"When I first examined this region in 1842, Professor 

 Hitchcock had already seen 2,000 impressions, each of them 

 indented on the upper sides of layers of shale, while the 

 casts of the same, standing out in relief, always protruded 

 from the lower surface of the incumbent strata. Had they 

 been concretions, as some geologists at first contended, they 

 would have been occasionally found projecting from the upper 

 sides of strata of sandstone. I was also much struck when 

 following each single line of foot-marks, to find how uniform 

 they were in size and how nearly equidistant from each other, 

 whereas on turning to a larger or smaller set of impres- 

 sions, the distance separating any two tracts in the same 

 series immediately increased or diminished, there being 

 an obvious proportion between the length of the stride 

 and the dimensions of the creature which walked over the 

 mud. 



"There are also a great number of examples where the trifid 

 impressions exhibit three marks of phalangeal bones for the 

 inner toe, four for the middle, and five for the outer one, as in 

 the feet of living tridactylous birds, and in each continuous 

 line of steps the three-jointed and five-jointed toes are seen to 

 turn alternately right and left. In one slab found at 

 Turner's Falls, on the Connecticut, by Dr. Deane, the fine 

 matrix has retained marks of the integument or skin of the 

 foot. This specimen is now in the museum of Dr. Mantell, 

 and the impression was recognised by Prof. Owen as resem- 

 bling the skin of an ostrich, and not that of a reptile. Such 



