CONNECTICUT RIVER SANDSTONE. 21 



those of the birds, in number or variety. A portion of this class of footprints 

 appears to indicate animals intimately related to existing saurian reptiles ; but 

 another portion of them, comprising several distinct varieties, cannot be compared 

 with any known type. They are both quadrupedal and bipedal, and, considered 

 as a class, possess extraordinary interest. 



The structural organizations of the extinct animals can only be inferred by 

 applying the laws of comparison to the impress of their feet; for the configura- 

 tion of the footprint presents the only practical basis for comparison, and it 

 fortunately happens that impressions occur so accurately defined as to supply, in 

 an eminent degree, an equivalent for the missing bones of the animal to whom 

 they are due. It would seem that the exact impress of the foot offers a basis 

 of analogy little inferior in value to the foot itself. We instinctively judge of 

 the physical organizations of familiar animals by their footprints; and the diffi- 

 culty in comprehending the organisms of the extinct animals lies, in a great 

 degree, in an insufficient acquaintance with the footprints of their living successors. 

 If living animals be found whose footprints conform in every essential particular 

 to the fossil impression, it must in reason be conceded, that the organization and 

 habits of the extinct and living types are also conformable. 



The comparison of the supposed ornithoid vestiges with the footprints of 

 living birds is unequivocal; a remarkable agreement exists between them; but 

 in the reptilian impressions, that do not usually ■exhibit the phalangeal divisions 

 of the toes, the grounds of analogy are not so clear. There are, moreover, 

 examples of this class of footprints, of a character so anomalous, as, in the present 

 state of science, to defy comparison. Certain forms of the footprints (PL 37) 

 indicate bipedal monsters, that, in respect to magnitude and intricate mechanism 

 of the feet, are without analogy in existing nature. The original from which 

 this Plate is reduced, is seventeen inches in length and eleven in breadth, and 

 its impress is without blemish. Other bipedal reptiles existed, that were distin- 

 guished for their diminutive proportions, whose footprints are represented in Plates 

 38 and 39. A formidable obstacle to comparison exists in the fact, that a certain 

 portion of the extinct animals appears to have been invested with diversified 

 powers of locomotion. It is presumed they could walk as quadrupeds (Pis. 

 33 and 34) or jump like the kangaroo (Pis. 31 and 32) ; and it may hereafter 

 be inferred that they could also walk upon their posterior feet as bipeds. If 

 this inference be sustained, we may look in vain for living representatives whose 

 powers of locomotion present such extraordinary combinations. 



