Ornithichnology. 311 



ing it with a chisel afterwards, the natural face of the layers is apt to 

 be marred : whereas it secfiis to have been often the fact, that the 

 sand and mud which filled the original track, are more firmly concre- 

 ted than the rock generally, and^^re thus rendered scarcely fissile at 

 all ; and while the rock around the track becomes shaky, so as ea- 

 sily to be cleaved off, the track itself remains unaffected ; and thus 

 with care, a fine specimen may be obtained. I doubt not, but the 

 quarrymen, had they known the nature of these relics, might have 

 saved in times past, many specimens of this kind : as I found frag- 

 ments of this sort among the rubbish thrown out of the quarry. 



There is one case, in which we do not see the layers of the rock 

 conforming to the depression produced by the track. It is when the 

 track was made in very fine mud, or clay, and the depression is fill- 

 ed by the same material in a concreted form. If in these circum- 

 stances, a layer of coarser materials, is superimposed, this layer often 

 exhibits no traces of the impression beneath. And I can easily con- 

 ceive how such a change of circumstances, (perhaps a sudden rise 

 of the waters,) as brought on the coarser materials, should have so 

 filled up the depressions as to leave a level surface for the deposition. 

 In such cases, we obtain specimens only in relief. 



In descending into the rock in a quarry, by splitting up the suc- 

 cessive layers, we first meet with the track in rather an imperfect 

 state, the toes being short and blunt. But by cleaving off a layer 

 or two, the impression becomes larger and more distinct ; and some- 

 times claws are visible. If we continue to cleave off layers beneath 

 where the impression is most perfect, we may find, perhaps, some 

 traces of it ; as for instance, the thickest or middle toe ; but it is 

 much sooner lost in descending, than in ascending from the layer 

 where it is most perfect. 



I early directed my attention to the enquiry, whether these tracks 

 could be traced in succession : that is, whether they were made by 

 an animal in the act of walking ; and I have been agreeably sur- 

 prised to find so many examples of this sort, of the most unquestion- 

 able kind. Drawings of some of the most remarkable of these, ac- 

 company this paper, (Figs. 1 to 10, with Fig. 15, 16, 17, 23 and 24.) 

 But a particular description of them will come in more convenient- 

 ly, in another place. In one instance, (Fig. 6.) it will be seen, that 

 no less than ten tracks succeed each other in such a direction, and 

 with so nearly equal intervals, that it is impossible to doubt that they 

 resulted from the continuous steps of an animal. Nor does there 



