1856.] 113 



only a part of the same extensive fresh water lignite formation observed by Sir 

 John Richardson on the Saskatchawan, of which we have little doubt, then it 

 is highly probable the Lignite and Goal formations mentioned by Mr. Isbister as 

 flanking the eastern slope of the Rocky Mountains, in the form of a continuous 

 belt from the Saskatchawan to the Arctic Ocean, belong to the same epoch. 



For the most part, these deposits in Nebraska consist of beds of gray, yel- 

 lowish, whitish, and blue sand, sandstone, clay, &c., with alternating strata of 

 lignite of variable purity, and carbonaceous matter mingled with much sand 

 and clay. These beds of lignite often take fire spontaneously, from heat gene- 

 rated in the decomposition of iron pyrites, and burn for many years at a time, 

 sending forth suffocating sulphurous vapors, and causing such an intense degree 

 of heat as to fuse the contiguous clay and sand into masses presenting every de- 

 gree of compactness, from that of obsidian to light vesicular lava. In some of 

 the argillaceous beds, great numbers of beautiful fossil plants are found, a fine 

 series of which was collected and placed for investigation in the hands of Dr. 

 J. S. Newberry, the well known fossil botanist of Cleveland, Ohio. The remains 

 of Mollusca collected from these formations, over a wide extent of countrj-, pre- 

 sent a remarkable uniformity of character, and as maybe seen by the following 

 paper, are all, excepting a few land shells, referable to genera usually found in 

 fresh and brackish waters. It is an interesting fact that the most nearly allied 

 living representatives of many of these species are now found inhabiting the 

 streams of Southern Africa, Asia, China, and Siam, apparently indicating the 

 existence of a tropical climate in these latitudes at as late a period as the Tertiary 

 epoch.* 



Although there can be no doubt that these deposits hold 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 synchronism 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 resemblance to the fossils of the Woolwich and Reading series of 

 English geologists, as well as to those of the great Lignite formations of the 

 south-east of France, would seem to point to the lower Eocene as their jjosition. 

 Yet it may be possible these resemblances have resulted from the action of pre- 

 cisely similar causes at a somewhat later period. 



It is a little remarkable that these formations differ in many respects from 

 those of the White river basin lying so near on the south. In the first place they 

 generally contain more sand, are usually characterized by beds of lignite, and 

 as yet have furnished no remains of Mammalia ; while the White river basin is 

 more argillaceous, appears to be destitute of lignite, and is well known to be one 

 of the most remarkable repositories of extinct mammalian remains on the face 

 of the globe. In addition to this, not one of the species of Mollusca in our col- 

 lection from the Lignite formations, is identical with any of those described by 

 Dr. Evans and Dr. Shumard from the White river basin. 



Formations immediately beneath the Tertiary in this district. 

 It would seem that the change of physical conditions which closed the Cre- 

 taceous epoch and ushered in the Tertiary, in this part of the world at least, was 

 gradual, not violent. We find that even while the Cretaceous conditions still 

 existed, (during the deposition of No. 5 of the seriesf ) the approaching close of 

 that state of things, and tlie coming of the Tertiary era, were foreshadowed by 

 the introduction of Fasciolaria^ Pleurotoma, and Belemnitella, with many shells of 

 other genera, quite as near in their specific affinities to Tertiary as to Cretaceous 



* We are under many obligations to Dr. Isaac Lea, of Philadelphia, for the 

 privilege of comparing our fossil species with analogous forms in his magnifi- 

 cent collection of recent shells. 



I For a section of the rocks of this country see a paper by James Hall and F. 

 B. Meek in the Memoirs. Am. Acad. Arts and Sci. vol. 5, New Series. Likewise a 

 paper by F. B. Meek and F. V. Hayden in Proceed. Acad. Nat. Sci. Phila., March 

 1856. 



