FOSSIL FOOTMAKKS OF BIRDS. 



15 



than nineteen inches, must have been twice the size of the 

 modern African ostrich. The distances between the smaller 

 measnre only about three inches, but in the case of the largest, 

 called the Ornithichnites gigas, they are from four to six 

 feet apart. In some places Avhere the birds have congregated 

 together none of the steps can be distinctly traced, but at a 

 short distance from this area the tracks become more and 



FOSSIL FOOTMARKS OF lilKUS. 



more distinct. Upwards of two thousand such footprints 

 have been observed, made probably by nearly thirty distinct 

 species of birds, all indented on the upper surface of tlie strata, 

 and only exhibiting casts in relief on the under side of the beds 

 which rested on such indented surfaces. In other ])laces the 

 marks of rain and hail which fell countless a^'es ao-o are clearly 

 visible. Sir Charles Lyell perceived similar footprints iu the 



