NATURAL SCIENCES OF PHILADELPHIA. 429 



ern States, as mainly representatives of the Upper Green Sand, or Chalk Marl 

 of Europe. It should not be forgotten, however, that he considered what he 

 had previously called the " Middle Division," that is, the upper calcareous 

 stratum in New Jersey, "contemporaneous with the European White Chalk."* 



Sir Charles Lyell expresses the opinion that the fossils of the New Jersey- 

 Cretaceous beds, "on the whole agree most nearly with those of the upper 

 European series from the Maestricht beds to the Gault inclusive." f 



Prof. Henry D. Rogers, with his usual sagacity in such matters, remarks in 

 his able Report on the Geology of New Jersey, that he does not regard the Green 

 Sands of that State, " in the strict sense of the word, as the equivalents of the 

 Green Sand formation, so called, of Europe." J 



In his Cours Elementaire de Palconlologie, Alcide D'Orbigny refers the fossili- 

 ferous Cretaceous beds in New Jersey, and those in Nebraska, Arkansas, Texas, 

 Alabama, &c, all to his Senonien, the equivalent of the White or Upper Chalk, 

 and Maestricht beds.g 



Prof. F. J. Pictet, in his " Traite de Paleontologies also refers most, if not all, 

 of the New Jersey Cretaceous species, to the age of the White Chalk of Europe. 



In an interesting paper read by Dr. Isaac Lea before the Academy, in Decem- 

 ber, 1858, he likewise seems to favor the conclusion that the Cretaceous Green 

 Sands of New Jersey represent the Senonien of D'Orbigny, but suggests some 

 reasons for thinking that they may possibly belong a little lower in the Series.|| 



From a careful review of the whole subject, and an attentive study of exten- 

 sive collections from the various formations of Nebraska, we are led to adopt 

 D'Orbigny's views, so far as regards our Upper Cretaceous Series of that re- 

 gion, and their equivalents in New Jersey and the States farther south. That 

 is to say, we regard these rocks as synchronous with the Upper or White Chalk, 

 and Maestricht beds of Europe, (= Senonien of D'Orbigny.) We differ with him, 

 however, in regard to the parallelism of our Lower Series of Nebraska; or, more 

 properly, we differ with him in referring equivalent beds in Arkansas and far- 

 ther south to his Senonien, for it is probable he had never seen any fossils from 

 this Lower Series in Nebraska. 



The evidence in fivor of the conclusion we have adopted in regard to the 

 synchronism of our Upper Series of Cretaceous rocks in Nebraska, with the White 

 Chalk and Maestricht beds of Europe, is both of a stratigraphical and paleon- 

 tological nature. The stratigraphical evidence is, that it holds, west of the 

 Mississippi, a position above an older series, containing, as we have shown, a 

 group of organic remains corresponding in their affinities, and in several in- 

 stances, as we think, agreeing specifically with Lower Chalk forms in the old 

 world. The paleontological evidence is, first, that many of its fossils belong 

 to genera, which, according to Pictet, D'Orbigny, and others, are not known in 

 Europe below the White Chalk, nor even, in some instances, below the oldest 

 Tertiary. Secondly, that several of the forms occurring in these beds in Ne- 

 braska are also found in equivalent beds in New Jersey, and farther south, asso- 

 ciated with well known European Upper Chalk and Maestricht bed species ; 

 while they are all specifically distinct, so far as known, from those found in the 

 Lower Series in Nebraska. 



The following is a list of the genera found in the Upper Series in Nebraska, 

 and equivalent strata in New Jersey, Alabama, and some other States in the 

 South ; which, according to trustworthy authorities, are not known to range 

 below the horizon of the White Chalk, and a few of them not even below the 

 oldest Tertiary at foreign localities.^ 



* Jour. Acad. Nat. Sci., vol. iii., New Series, p. 217. 1841. 

 t Manual, p. 224. 



X Report on the Geology of New Jersey, page 178. 1845. 

 || Cours Elemt. de Paleontologie, pages 671 and 672, vol. ii. 1852. 

 I Proceed. Acad. Nat. Sci., Phila., Dec, 1858. 



\ A few other genera might probably be added to this list, but we have given what we 

 consider the best authenticated examples. 



1861.] 



