INTRODUCTORY REMARKS. XXI 



mens, however, were taken along, and such progress as a feeble slate of health 

 would permit, was made in writing out portions of the text. 



Being compelled by the continued infirm condition of his health to pass 

 the succeeding winters in Florida, and the sultry summer months out of the 

 city, the author has necessarily had to complete the work away from many 

 desired facilities. The difficulties, therefore, under which he has labored 

 during the preparation of this report and its passage through the press, will, 

 it is hoped, be a sufficient apology for its long delay, as well as for such 

 imperfections as may catch the eye of the critical reader. 



In regard to the progress of geological discoveries, and the nature and 

 extent of the geological formations, in the remote country from which the 

 collections here described were obtained, some preliminary remarks seem 

 to be necessary here. These remarks will commence with the extensive 

 marine series of undoubted Cretaceous age; after which the later Lignite 

 formations of brackish- and fresh-water origin will be considered ; and, 

 finally, the still more modern Tertiary beds, mainly of fresh water origin, 

 will be noticed. 



CRKTACEOUS FORMATION. 



Commencing with the earliest explorers of the Upper Missouri, the 

 first intimations of the existence of Cretaceous deposits there, seem to have 

 beeu derived from specimens obtained by Lewis and Clarke during their' 

 expedition to the sources of the Missouri, and across to the Columbia, in 

 1804, 1805, and 1806. Subsecpiently, Nuttall, and later, Colonel Long, 

 brought from this country a few Cretaceous fossils; and in 1832, the Prince 

 of Neuwied discovered the remains of Mosasaurus Missouriensis, and other 

 Cretaceous types, at the Great Bend, below Fort Pierre. None of these 

 explorers, however, seem to have given attention to the structure and 

 geographical extent of these Cretaceous rocks, or to the order of succession 

 of their subdivisions. 



In 1839, the geographer Nicollet ascended the Missouri to Fort Pierre, 

 collecting on his way up, at the Great Bend and other localities, a number 

 of Cretaceous Molluscan remains.* Although passing rather rapidly through 

 the country, he formed a tolerably correct idea of the subdivisions of the 

 Cretaceous rocks seen by him below Fort Pierre. He seems, however, not 



"These collections were figured and described by Dr. Morton iu the Journal of tbe Acad. Nat. Sci. 

 Philad., VIII, -207, 1839. 



