EEPTILES ABUNDANT. 69 



of an animal, in the act of walking or running, with the right 

 and left foot always in their relative places. The distance of 

 the intervals between each footstep on the same track is occa- 

 sionally varied, but to no greater amount than may be explained 

 by the bird having altered its pace. Many tracks of different 

 individuals and different species are often found crossing each 

 other, and crowded, like impressions of feet upon the shores of 

 a muddy stream, where ducks and geese resort." 1 Some of 

 these prints indicate small animals, but others denote birds of 

 what would now be an unusually large size, one having a foot 

 fifteen inches in length, and a stride of from four to six feet. 

 There are anomalies in the forms of some of the feet ; but their 

 being the vestiges of birds has for some years been generally 

 admitted. There is, however, some uncertainty regarding the 

 date of the rocks which present these memorials, for the pheno- 

 mena of superposition only denote their being between the 

 carboniferous and cretaceous formations, and an exact place is 

 assigned them, merely upon the strength of the discovery that 

 they present fish of certain genera never found above the 

 Triassic series. Along with distinctly ornithic footmarks are 

 those of the Labyrinthodont. Altogether, above thirty species 

 of Triassic birds are made out from these tracings by American 

 geologists. 2 



OOLITE. 



The chronicles of this period consist of a series of beds, 

 mostly calcareous, taking their general name (Oolite sy stein) 

 from a conspicuous member of them the oolite a limestone 

 composed of an aggregation of small round grains or spherules, 

 and so called from its fancied resemblance to a cluster of eggs 

 or the roe of a fish. This texture of stone is novel and striking. 

 It is of chemical origin, each spherule being an aggregation of 

 particles round a central nucleus. The oolite system is largely 

 developed in England, France, Westphalia, and Northern 

 Italy ; it appears in Northern India and Africa, and patches 

 of it exist in Scotland, and in the vale of the Mississippi. It 



1 Dr. Buckland (Bridge water Treatise), quoting an article by Professor 

 Hitchcock in the American Journal of Science, 1836. 



2 In 1847, Professor Pleininger, of Stuttgard, published a description 

 of two fossil molar teeth, referred by him to a warm-blooded quadruped, 

 which he obtained from a bone breccia in Wurtemburg, occurring be- 

 tween the lias and keuper. He regarded them as the teeth of a preda- 

 ceous mammal. 



