WARD.) HISTORICAL REVIEW OF OPINION. 407 



vestigation, which tliey soou received at the competent hands of Messrs. 

 Meek and Leidy. In the first of the papers above referred to,' in which 

 all the species described are mentioned as Cretaceous, the authors 

 remark : " It is worthy of note that some of the species contained in the 

 collection from the most recent Cretaceous beds of the Upper Missouri 

 country appear referable to genera which, according to high European 

 authority, date no farther back than the true chalk, while many of them 

 are closely analogous to Tertiary forms ; so close, indeed, that, had they 

 not been found associated in the same beds with Ammonites, Scaphites, 

 and other genera everywhere regarded as having become extinct at the 

 close of the Cretaceous epoch, we would have considered them Tertiary 

 species." A section is given, at the top of which 400 to 600 feet of 

 "Tertiary" are placed, which is described as " beds of clay, sandstone, 

 lignite, &c., containing remains of vertebrata, and at places vast num- 

 bers of plants, with land, fresh- water, and some times marine or estuary 

 mollusca." 



At the next meeting of the Academy, Dr. Joseph Leidy read a paper 

 in which he described the vertebrate remains which Dr. Hayden had 

 obtained from the Bad Lands of the Judith River. He is silent as to 

 the age which these remains indicate until the close of the paper, where 

 he names a species of Lepidotus in honor of the discoverer, and says : 

 "This species is named in honor of Dr. Hayden, who collected the re- 

 mains characterized in this paper ; and which remains, I suspect, indi- 

 cate the existence of a formation like that of the Wealden of Europe;" 

 a remark which has since been much quoted in support of the Mesozoic 

 age of the Judith River beds. 



On June 10th of the same year a second paper was presented to the 

 Academy by Messrs. Meek and Hayden, entitled " Descriptions of new 

 species of Acephala and Gasteropoda, from the Tertiary formations of 

 Nebraska Territory, with some general remarks ou the Geology of the 

 country about theusources of the Missouri River." 



These " general remarks," which were " based upon the observations 

 and collections of Dr. Hayden," contain some very interesting state- 

 ments and certain somewhat remarkable adumbrations of the conclu- 

 sions to which tbe latest investigations have led respecting the geology 

 of this region. The liguitic deposits are regarded as Tertiary, but they 

 are very clearlj' distinguished from the fresh-water deposits of the 

 White River group as well as from the underlying Cretaceous formation. 

 "Although there can be no doubt," the authors- say, " that these deposits 

 bold a rather low position in the Tertiary system, we have as yet been 

 able to arrive at no very definite conclusions as to their exact synchro- 

 nism with any particular minor subdivision of Tertiary, not having 

 been able to identify any of the mollusca found in them with those of 

 any well marked geological horizon in other countries. Their general 



' Proceedings of the Academy of Natural Sciences, Philadelphia, Vol. VIII, 1856, p. 

 63. (Read March 11.) 



