408 



proofs of deposition in turbulent waters are most remarkable, and 

 the sediments are quite variable, though seldom so coarse as to become 

 a conglomerate, varying from a rather fine sandstone to a pudding- 

 stone. In this bed of sandstone are many irregular seams of indu- 

 rated clay, sometimes simply tilling small pockets or thin seams, 

 extending only a few feet horizontally. It was in one of these seams 

 of clay, about four feet thick, near the summit of the bed of sandstone, 

 that a portion of the plants described in the preceding paper by Mr. 

 Lesquereux were found. This sandstone appearsto hold a position beneath 

 all the workable beds of coal in this region, and from its thickness 

 and massiveness forms a marked horizon. It is full of holes, cavi- 

 ties in some instances so large as to be called caves, worn out by the 

 water which has trickled down from the top, the soft clay portions washing 

 out most readily, so that the face of the rocks is often very rugged, pre- 

 senting a most fantastic appearance. Sometimes the rock is literally 

 honey-combed. The layers of deposition are so irregular that a mass in 

 the center of the bed of sandstone, twenty or thirty feet thick in the 

 middle, tapers to a point at each end within a horizontal distance of 

 one hundred feet. Immediately above this sandstone at this locality 

 are several beds of coal, four to six feet in thickness, and above and 

 below these beds of coal are great quantities of oysters of several 

 varieties and a species of Corhlcula. It will be observed that everywhere 

 the genus Ostrea, and in many instances A)iomki, extend up into the 

 brackish-water beds, and that eveu on the Upper Missouri, where these 

 Lignitic beds were first discovered and pronounced to be of Miocene 

 age, Ostrea and other brackish-water forms of MoUusca were found in the 

 lowest strata. The group of plants described by Lesquereux from this 

 sandstone are, so far as I know, from the lowest horizon in the series 

 in which plants have been found up to this time. As Lesquereux re- 

 marks, the plants must represent a horizon very near the true Creta- 

 ceous beds, inasmuch as several of the species have strong Cretaceous 

 aflinities. At Eock Springs not a plant was found by me, and I cannot 

 not ascertain that any one else has observed any at this locality. 

 A species of Corhicula was rather abundant in the clay over the work- 

 able bed of coal. 



It is not my purpose to present any details of the season's work in 

 these notes. They are intended, to be rather explanatory of my former 

 views and the views I hold at present in regard to the important prob- 

 lem — the age of the Lignitic group in the West. So far as sections are 

 concerned, as well as a most careful and accurate study of the forma- 

 tions from Bitter Creek to Coalville, the very detailed and interesting 

 reports of Mr. F. B. Meek and H. M. Bannister in the Annual Eeport 

 of the Survey for 1872 may be consulted. 



With our present knowledge, we may separate the Lignitic beds, above 

 what is usually understood as the Cretaceous Fox Hills group, into 

 three divisions : 1st. The strictly marine strata, like those bearing coal 

 at Bear Eiver and Coalville; 2d. The mixed or brackish-water beds; 

 3d. The purely fresh-water strata, of which the upper portion of the 

 Lignitic group of the Northwest is an excellent example. The first group 

 contains abundant well-marked Cretaceous forms; yet even in this 

 division, the physical changes which we find at later date were fore- 

 shadowed by the mingling of a few brackish-water species. The genus 

 Inoceramus, which has always been relied upon as strong proof of the 

 Cretaceous age of beds in which it occurs, is found both at Bear Eiver 

 and Coalville in great abundance. 



Eeaching a certain horizon, we gradually approach a second group of 



