280 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



CRETACEOUS FORMATION. 



The middle and lower portions of the Cretaceous formation are not prominently 

 developed along our route. I have, in the foregoing chapter, mentioned that this 

 division of the Cretaceous strata, No. TIT, and, probably, also Nos. I, II, and IV of 

 the Nebraska section, are exposed above the Jurassic rocks between the Platte Bridge 

 and the Red Buttes. and I have described their character. Farther eastward the over- 

 lving Lignite formation covers the surface. Only about two miles above Deer Creek, 

 I noticed grav and brown laminated, impure sandstone, wirli slialy portions and car- 

 bonaceous particles, and found in it some imperfect fossil bivalves, which are referred 

 by Mr. Meek to the genus Vmtopiwa and the upper part of the Cretaceous system. 

 The lithological character of the rock corresponds to that of the upmost Cretaceous 

 l, t . ( ls — \,, # \ () f the Nebraska section — which are described as yellow arenaceous and 

 argillaceous grit, containing much ferruginous matter; it also closely resembles that of 

 some portions of the Lignite formation. Loose pieces of a hard, brown sandstone, 

 with a species of Inocrramua (see Mr. Meek's report), which seems to indicate that the 

 bed from which they come holds a position at the base of No. IV of the Cretaceous 

 section, have been found at several points near the last-mentioned locality, some dis- 

 tance higher up on Platte River, and again a few miles west of the Red Buttes. These 

 specimens apparently have not been drifted far, but I could not ascertain from which 

 strata they come. 



1 am led to consider the Lignite formation on Platte River, along our route, as 

 Upper Cretaceous, corresponding to the one near Bryan's Pass and the Medicine Bow 

 Butte. 



The Cretaceous formation is considerably developed farther south in this section 

 of country. While with Lieutenant Bryan, Topographical Engineers, in 1856, 1 have 

 observed beds, corresponding apparently to No. IV, on the eastern slope of the Black 

 Hills, near the South Platte. Speaking of them, I remarked (Report Secretary of 

 War, December. 1857, p. 510): "Near the place where Cache-la-poudre Creek breaks 

 through the last chain of rocks to enter the plains, I observed in the sandstones inter- 

 stratifications of altered sandy shales and shaly limestones. Some of these were highly 

 fbssiliferous, full of remains of fishes and shells, and fetid from the large amount of 

 organic matter. The fossils are, however, preserved badly. They are undoubtedly 

 Cretaceous." One of them appears to be Lion ramus S(((/citsis, which, in Nebraska, is 

 confined to the upper part of No. IV. 



No. Ill was then found largely and characteristically developed along Sage Creek, 

 an affluent of North Platte River, near the divide between Platte and Green Rivers, 

 and also on the northeastern side of the Medicine Bow Butte. No. II was observed 

 south of that butte: "There were several layers of a finely-grained, subcrystalline, 

 fetid limestone, which is in some places even bituminous, from the large amount of 

 organic remains which it includes. Other portions contain a great deal of micaceous 

 sand, so much so as to change it into a micaceous sandstone." Fossils were abundant, 

 and evidently of Cretaceous age. Lately the specimens from there have again been 

 carefully examined, and the result shows that this formation is No. II of the Cretaceous 

 series. An Ammonites is closely allied to Ammonites percarinatus, which occurs in No. 



