3Iesozoic and Connozoic Geology and Palceontology, 17 



found north of the line above indicated, covering the whole area of 

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

 iferous strata and granitic rocks. The Cretaceous strata constitute, 

 generall}', compact and hard rocks, some of them equaling in compact- 

 ness the hardest strata of more ancient secondary formations. Gener- 

 ality 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 dry 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, 

 Crocodilus basf/issus, C. hasitruncatiis^ now Holops basitruncatus^ 

 Ilacrosuurus loivis and Hyposaurus r oyer si. 



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

 Catopygus oviformis. 



In 1851, Dr. Gibbes]; described, from South Carolina, Jlosasaiirus 

 ((catidens.M. brumby i, 31. caroUnensis, 31. couperi, and 31. minor. 

 And Dr. Leid3'§ described Biscosaurus vetustus, now Cimoliasaurus 

 vetustus, and Conosaurus b&wmani. 



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

 Ammonites nebrascensis^ A. cheyennensis, now Scaphites cheyennensis, 

 A. opalus, A. moreauensis, now S. moreauensis, A. lenticularis, now 

 Placenttceras lenticulare, Scaphites comprimus., 8. nodosus., Ino- 



■■' Quar. Jour. Geo. Soc, vol. 5. 



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



X Smithsonian Contributions, vol. 2. 



§ Proc. Acad. Nat. Sci. 



1 Kep. Geo. Sur. Wis., Iowa and Minn. 



