332 - Orniihichnology. 



pies of geology. He sees that the rock on which the impressions 

 are made, is composed of mud and sand ; and although he may not 

 be able to explain how these materials were consolidated, yet he can 

 hardly doubt but this rock was once in a soft state, and that these 

 tracks were then made. 



Thus far, it seems to me, all mubt agree. And when, as already 

 remarked, we see upon the mud that covers these rocks, where they 

 pass under the waters of the Connecticut, the tracks of living birds, 

 exceedingly analagous to those upon the dry rocks, can we doubt 

 that we witness the precise mode in which the ornithichnites were 

 produced ; — and especially when we find that the character of the foot, 

 and the length of the step, indicate that most of the birds that form- 

 ed them, must have had the habits of the existing waders or'Grallse, 

 we cannot but infer that the impressions on the ornithichnites were 

 made by the birds of the new red sandstone era, that frequented the 

 margins of estuaries, streams and lakes, whose muddy shores, where 

 they trod, were afterwards converted into the existing rock. 



I know it has been usual, to regard the early geological chan- 

 ges on the globe, as having taken place in a very different manner, 

 from those which are now going on ; and I cannot resist the con- 

 viction, that the intensity of the causes has varied exceedingly at 

 different times ; but this could affect only the magnitude, not the 

 similarity, of the results; and I have been struck with 'the remark- 

 able resemblance between the state of things, as shown by these 

 ornithichnites, to have existed so many thousands of years ago, and 

 that now passing before our eyes. Our imaginations are carried 

 back by these relics, to that immensely distant period, when the new 

 red sandstone birds were travelling along the shores of the then ex- 

 isting estuaries or lakes, just as is now done by congeneric races. 



There is, however, one striking point of difference between the 

 ancient and the modern races. I refer to the enormous size of ma- 

 ny of the former. Some, indeed, appear to have been no larger 

 than the smallest of existing birds of their class : but what shall we 

 say of those that produced the O. giganteus and ingens, taking 

 'Strides of four feet, as their ordinary step ! As to their real size, we 

 may forever be left to conjectures. But I am not sure that a practic- 

 ed comparative anatomist, could not determine the size of a bird, 

 having the size of the feet, and the length of the step given. I shall 

 not attempt the problem any farther than to state one faci by way of 

 comparison. The African ostrich, (^Struthio camelus) the largest of 

 known birds, has a foot only ten inches long, reckoning from the back 



