MEXICAN BOUNDARY LINE. ~ 129 



three-fold division, in which the upper member consists of the "rotten limestone," the central 

 an arenaceous group, and a lower dark colored clay. 



Without at present having the means of exact comparison, it may be inferred that there is a 

 close agreement between the different members of the series in Alabama and New Jersey. The 

 specific identity of many of the characteristic fossils leaves no doubt as to the close similarity of 

 the formation there developed, with the beds in New Jersey, from which a large part of the 

 fossils described by Dr. Morton were obtained. The calcareous part of the formation in 

 Alabama acquires a far greater development than in New Jersey, and appears to be there the 

 principal repository of the fossils of this period. 



It is now more than fifty years since Messrs. Lewis and Clark, in their expedition to the 

 Columbia river, brought from the Great Bend of the Missouri river some fossils, which were 

 afterwards identified by Dr. Morton as belonging to the cretaceous formation, and from beds of 

 the same age as the marl or ferruginous sand of New Jersey, Delaware, and Alabama. Subse- 

 quently Mr. Nuttall brought some species from the same locality. Dr. Morton, ia his Synopsis, 

 (1834,) acknowledges the receipt of Gryphcea Pitcheri and other cretaceous fossils of great interest, 

 from the plains of Kiamesha, in Arkansas, from Dr. Z.Titcher, of the United States army. Dr. 

 Morton also mentions other fossils from the falls of Verdigris river, in the same Territory. 



It is nearly twenty years since Mr. Nicollet first visited and explored the country about the 

 sources of the Mississippi and some parts of the Missouri river, as far up as Fort Pierre. The 

 collections made by this gentleman enabled Dr. Morton to designate about sixteen species of 

 cretaceous fossils, half of which were regarded as common to that region. New Jersey, and 

 Alabama. Mr. Nicidlet, in his report, has given the following section of the beds of the 

 cretaceous formation upon the Upper Missouri : 



D. — A plastic clay deposit, about 200 feet thick, divided into two equal parts by a stratum of 

 carbonate of lime in nodules. 



C. — A ferruginous clay, of a yellowish color, containing masses resembling septaria and 

 seams of selenite. 



B. — A calcareous marl, generally from 30 to 40 feet thick. 



A. — " Argillaceous limestone, containing Inoceramus Barahini (?) in great numbers, and very 

 much compressed, and so arranged as to give the rock a slaty appearance."* — (At Dixon's Bluff.) 



The importance of these divisions does not appear to have been fully appreciated, or the col- 

 lection was not sufficient to establish the restriction of species within the limits thus indicated. 



In the meantime, the explorations of Lieutenant Fremont, of Lieutenant Abert, of Captain 

 Stansbury, and others, and more extended examinations made under the direction of Dr. D. D. 

 Owen, in his Geological Survey of the Chippewa Land District, have brought to light other 

 cretaceous species from this region ;t while the several Pacific railroad surveys have shown the 

 occurrence of cretaceous fossils at various points farther to the south, and at intervals which 

 indicate a continuation of the formation from the Missouri river to New Mexico. More recently, 

 Dr. Evans, who had previously visited this region as assistant in the geological survey of Dr. 



• The species of Inoceramus in Mr. Nicollet's collection, in a condition here described, was subsequently identified by me as 

 the same with that brought by Captain Fremont from tho Smoky Mill river. — (See rrport, p. 310.) 



t In his report Dr. Owen does not notice the subdivisions of Mr. Nicollet's section ; and the cretaceous speeies figured and 

 described appear all to have been derived from a single bed of the formation. 



17 M 



