conceive 



336 ^ Ornithichnology . ^ , 



position, without injury; and if the cause continued to act, as the 

 successive layers were deposited, might not all the disturbance which 

 we witness, have been thus produced ? Or, suppose the track was 

 made on very yielding mud, which had a rapid slope beneath the 



how, as the new layers of mud 

 were deposited, the mere force of gravity would cause them slightly 

 to descend, and thus carry downward the track, without effacing it? 



I have asserted that these tracks must have been made in a spot 

 which was constantly, or frequently, beneath the waters ; for if made 

 on dry land, instead of having a new deposit brought over them qui- 

 etly, to preserve them, they would be exposed to rains, and other 

 denuding and disturbing agencies, that must speedily deface, if not 

 obliterate them. Judging from what we now see of the tracks of 

 living animals, a single month, nay, often a single week, or a day, 

 would be sufficient to destroy them. And even if, in some rare 

 cases, abundant rains and floods might cover the spot with a new 

 deposit, yet ordinarily the action must be so violent, as to ruin the 

 track ; but beneath the quiet waters of an estuary, or lake, or even 

 of a large river, after a few layers of mud had been brought over 

 them, they might remain, for aught I can see, age after age, unin- 

 jured. The quiet waters above them would be their security. For 

 these reasons, I suspect, that in almost every case, these tracks must 

 have been made beneath still waters. I can, indeed, conceive it 

 possible, that a track might be preserved, although made above low 

 water mark, provided that an early but not violent rise of the waters 

 should cover it with a thick deposit of mud. And yet the chances, 

 even in such a case, are very much against its preservation, loOj, 

 enough to be converted into stone ; so that, whatever objections the 

 ornithologist may raise, against admitting that all the tracks which 1 

 have described were made by t^rallfe, it seems to me, that the exi- 

 gencies of the case require us to suppose them produced by birds, 

 whose" habits were those of Grallas. 



The most Interesting aspect in which the facts that have been sta- 

 ted present themselves to the geologist, is as to the evidence they a - 

 ford of the very early existence of birds, among the inhabitants of our 

 globe. Heretofore there has been no proof of their existence, un- 

 til within a comparatively recent period. But it now appears, t a 



the earliest of the vertebral animals that were 



anion u; 



globe. The discovery 



veals the history of a people, a few hundred years earher than ha 



before 



