Mesozoic and Cmnozoic Geology and Palceontology, 53 



found north of the line above indicated, covering the whole area t)f 

 country with the exception of small exposures of Sihiriau and Carbon- 

 iferous strata and granitic rocks. The Cretaceous strata constitute, 

 generally, compact and hard rocks, some of them equaling in compact>- 

 ness the hardest strata of more ancient secondar}^ formations. Gener- 

 ally there is an alternation of compact silicious limestones, and less 

 compact beds of either pure or marly limestone. The former contain 

 the silex as well diffused through their whole mass, as in separate con- 

 cretions or nodules. The silicious character of these rocks, excluding 

 the decomposing action of the atmosphere, almost entirely' produces 

 the general dr}^ and barren aspect of the country which they occupy. 

 He pointed out the differences between the Cretaceous fauna of Texas, 

 and that of New Jersey and other northern localities, and compared 

 the fauna with that of Europe, from whence he concluded that there 

 must have existed at the time of the Cretaceous period between the 

 continents of Europe and America, such a relation that, in both, the 

 same modifications in the zoological character distinguished the marine 

 fauna of the north from that of the south. From thence he drew 

 the interesting conclusion, that the same southern inflection of the 

 isothermal lines, which is at present so remarkable in their course 

 from the west side of the continent of Europe, toward the east side of 

 the continent of America, already existed at a period of the globe as 

 remote as that of the Cretaceous formation. 



In 1849, Prof Owen* described, from the greensand of New Jersey, 

 Vrocodili's basi'/issas, C, basitrtincatifs, now Holojis basitruncatus, 

 Macrosaurus loivis and Hyposaurus rogersi. 



In 1850, T. A. Conradf described, from Timber Creek, New Jersey, 

 Co.topygus oviformis. 



In 1851, Dr. GibbesJ; described, from South Carolina^ Mosasaurus 

 acutidens, M. brumbyi, If. carolinensis, 31. couperi, and 31. minor. 

 And Dr. Leid3§ described Discosaurus veiustus, now CimoUasaurus 

 vetustus, and Conosaurus bowmani. 



In 1852, Dr. D. D. Ovven|| described, from the Fox Hills of Nebraska, 

 Ammonites nebrascensis, A. cheyennensis,i\QW Scaphites cheyennensis, 

 A. opalus, A. moreauensis, now 8. moreauenst's, A. lenticularis, now 

 Placenticeras lentlculare, Scaphites comprimics, S. nodosus, Ino- 



'■'- Quar. Jour. Geo. Soc. vol. 5. 



t Jour. Acad. Nat. Sci., 2d ser. vol. 2. 



I Smithsonian Contributions, vol. 2. 



I Proc. Acad. Nat. Sci. 



i Rep. Geo. Sur Wis., Iowa and Minn. 



