Prof. Hitchcock on IchnoUthology, or Fossil Footmarks. 315 



Mr. Redfield informs me, to the Hamilton group. It contains 

 one peculiar fossil in considerable abundance, exactly resembling 

 an annelidous worm, but whose nature has not been ascertained, 

 although it is often very distinct. This group of rocks also 

 contains plants, according to Prof. Mather, who has described the 

 rock in his report. It is a hard, gray, rather thick bedded sand- 

 stone, of a very enduring character. 



Fig. 9, is an exact reduced copy, with the pentagraph, of the 

 slab in my possession. The impressions upon it appear to have 

 been made with a blunt object, nearly of the size of a man's 

 finger, and as much rounded. I regard these marks as resulting 

 from the agency of animals for the following reasons. 



1. The impressions are for the most part arranged in nearly 

 parallel rows ; the axis of the impressions lying nearly crosswise 

 to the direction of the rows. Thus on fig. 9, we can trace the 

 rows if I mistake not, A B, C D, E F, G H, L M, N 0, P R, S T ; 

 although some of the impressions are a little out of line. 



2. The impressions, like the Ornithoidichnites, appear to have 

 been produced by some body pressing on a surface of mud, rather 

 than by a body interposed between two layers of mud. 



3. There is such a general resemblance between the impres- 

 sions, as to prove them to have originated from the same general 

 cause. And yet they are of different sizes in the different rows, 

 but uniform for the most part in the same row. 



4. A large part of them are in pairs ; one of each pair being 

 considerably shorter than the other, and the axes of the two im- 

 pressions diverging pretty uniformly about 40°. On several parts 

 of the slab they are but imperfectly preserved. Had they all 

 been retained, I apprehend that they would be found universally 

 in pairs, since those most distinct are so. 



5. I know of no other agency but the feet of animals, to which 

 these impressions can be referred. They belong to no variety of 

 ripple marks, nor to the mud furrows and wave lines of Mr. Hall, 

 nor could they have resulted from lateral pressure, or the deposi- 

 tion of vegetable or animal remains. But they exhibit a general 

 resemblance to the tracks of animals. 



But what class of animals could have produced such tracks ? 

 Most probably an animal with didactylous feet in which one of 

 the toes is longer than the other. It had occurred to me that they 



