Association of American Geologists and Naturalists. 253 



(he yellow sand are species common in the lower or greensand division, 

 Ostrea falcata being one, may not some doubt exist, I would suggest, as 

 to the expediency of placing the intermediate straw-colored limestone so 

 definitely on the parallel of the chalk of Europe ? Influenced by the 

 fact just mentioned, and the still more weighty consideration that the 

 American strata in a list of about one hundred and sixty organic forms 

 contain probably not more than six or eight species in common with the 

 cretaceous rocks of Europe, I may be allowed to repeat a suggestion 

 made in my Report on the geology of New Jersey, that a further com- 

 parison of the organic remains is required, before we can determine 

 more than approximately the degree of affinity between the several di- 

 visions of the cretaceous series of the two continents. Mr. Lyell, who 

 when in this country collected, with Mr. Conrad's assistance, a some- 

 what extensive group of fossils from the straw-colored limestone of New 

 Jersey, will probably soon give us a more ample insight into the exact 

 degree of affinity subsisting between this stratum and the chalk. \ 



According to Dr. Morton, the shells hitherto ascertained to be com- 

 mon to the cretaceous deposits of Europe and America, are four : 7ri- 

 gonia alceformis, Pecten quinquicostatus^ Ostrea falcata and Gryphea 

 vomer ; and to these links he adds about four species of fishes, and that 

 strange gigantic oceanic lizard, the Mososaarus. To these points of 

 agreement we must add those of mere analogy in the remarkable generic 

 affinity of the fossils of the two distinct cretaceous basins. But even in 

 some of the more positive links above named, we recognize in the dis- # 

 wepancies of their position in the two series of deposits, the difficulty of 

 establishing an exact equivalency between the strata of basins originally 

 ^connected. Thus, while the Pecten quinquico status of our greensand 

 °r lower cretaceous group is absent from the middle and upper divisions, 

 which have been placed on the same horizon of time with the chalk of 

 Eur ope, it occurs on that side of the Atlantic in all the strata of the 

 •**«$ and again, the Ostrea falcata, restricted 1 believe in Europe to 

 toe limits of the chalk or upper cretaceous group, abounds in this coun- 

 ty chiefly in the lowest and disappears in the middle. In these in- 

 stances we see exemplified a general and important law concerning the 

 distribution of fossils, which is, that those species whose geographical 

 dls tribution is the widest, possess likewise the greatest vertical range, or, 

 ad apted to a greater variety of localities and physical conditions, they 

 hav e been suited to withstand a greater scries of vicissitude, and to en- 

 dur e therefore a longer time. Such, though usually styled the charac- 

 teristic fossils, are in reality the least characteristic of all ; for, while 

 Vol. XLVII? No a# _ Jll iy^ Septi 1844. 33 



