Chap. I. FOSSIL TURTLES. 303 



though the smallest of all Testudhiata are fresh-water species. But it must not 

 be forgotten, that these belong to the temperate zone, while the largest land Turtles 

 are exclusively tropical. Gigantic Testudinata, approaching the size of the largest 

 land Quadrupeds, are known among the fossils. 



SECTION XVII. 



FIRST APPEARANCE OF TESTUDINATA UPON OUR GLOBE. 



Though the period of the first appearance of the Testudinata upon the surface 

 of our globe has been a point of discussion among naturalists, even within the last 

 few years, I do not intend to enumerate here the fossil representatives of this 

 order, now satisfactorily known, nor even to compare the diflerent Turtles which 

 have existed, in former age.s, in North America, with those now living. My 

 object, for the jiresent, is simply to point out the period at which this remark- 

 able type of animals finst made its appearance, and at the same time to show 

 how important critical investigations are with reference to the affinities of fossil 

 and living animals, and how utterly impossible it is to arrive at any general 

 result respecting the order of their succession in time without such a close and 

 careful study. Only five years ago. Sir Charles Lyell published a supplement to 

 the third edition of his Manual of Elementary Geology,^ intended chiefly to sus- 

 tain the view that Reptiles had existed much longer upon the surfiice of our globe 

 than was generally supposed, and that the Chelonians in particular could be traced 

 back to the Potsdam sandstone, that is, to the lowest stratified set of beds in 

 which fossils had been found at all. The identification of these animals rested 

 iipoa footprints which had been examined by Professor Owen, Avho published a 

 description of these impressions early in the year ISol.^ This rejjort has since 

 gone the rounds of all the scientific and other jjeriodicals, and is now repeated 

 in almost every modern text-book of Geology and Palaeontology, though Owen him- 

 self has recognized his mistake,^ and in the following year puljlished his opinion, that 



* LycU's ^[aiiiKil of Elementary Geolojry. Post- first notice in London, an alistract of it was eomnuini- 



seript to llic tliird edition, London, Dceenilicr KUli, cated to the Ameriean Association for the Advance- 



1851. nient of Science, during its raeetinjr at Cincinnati, 



' Description of the Impressions on the I'otsdam I^Iuy, 1851, wliich led to a discussion, in wiiidi I ex- 

 Sandstone, discovered hy Mr. Logan, in Lower Can- pressed my conviction, based partly on physiological 

 a(hi, (jiiarterly .hmrnal of tlie Geological Society, ground.^, and parllv on the I'xaininalion of similar 

 London, 1851, vol. 7, p. 250. impressions, that they were the tracks of some paloe- 



' A few days after Professor Owen had rea<l his ozoic Crustacean, and not those of a Reptile. 



