310 Ornithichnology. 



run into one another, as the toes approach the point of convergence : 

 but they also sometimes stop short of that point, as if the animal had 

 not sunk deep enough to allow the heel to make an impression. 

 Nay, at that point the stone is in some cases irregularly raised, as if 

 the weight of the animal had caused the sand or mud to crowd up- 

 Avards in the rear of the step. In a few instances, also, behind this 

 slight elevation, there is a depression as if a knobbed heel had sunk 

 slightly into they yielding mass. 



In a large number of instances, also, there is a remarkable appen- 

 dage to the hind part of the impression. There radiates from it in 

 the rear, in the larger tracks to the distance of several inches, the 

 apparent impression of stiff hairs, or bristles. The drawings ap- 

 pended, will convey as good an idea of this appearance, as I can 

 give. 



In all cases where there are three toes pointing forward, the mid- 

 dle toe is the longest ; sometimes very much so. In a majority of 

 cases, the toes gradually taper, more or less to a point : but in some 

 most remarkable varieties they are thick and somewhat knobbed, 

 and terminate abruptly. 



In the narrow toed impressions, distinct claws are not often seen, 

 although sometimes discoverable. But in the thick toed varieties, 

 they are often very obvious. Much, however, in respect to this ap- 

 pendage, depends upon the nature of the rock. If it be composed 

 of fine clay, the claws are usually well marked. And then again, 

 if we chance to cleave the rock a httle above, or a little below the 

 layer, on which the animal originally made the impression, the claws 

 will be very likely not to be visible ; as I shall show more clearly 

 farther on. 



If we lift out of its bed a portion of the rock, several inches thick, 

 on which one of these impressions exists, and break it so that the 

 fracture shall pass across the toes, we shall see on the edge, the suc- 

 cessive layers of the rock bent downward, often two, three, or even 

 four inches in thickness. If we carefully cleave open the specimen 

 thus raised, on one face we shall have a ternary depression, as has 

 been described ; and on the other face, a correspondent figure, pro- 

 jecting more or less, sometimes in high relief. And these specimens 

 in alto relievo often give us a better idea of the structure of the foot 

 that made the impressions, than those that are depressed. For often 

 it is difficult to cleave a specimen so perfectly, that the portions of 

 the rock which fills the depression, shall all be got out ; and in do- 



