324 GEOLOGICAL SURVEY OF THE TEERITORIES. 



sand-rock too, many remains of fiicoidal plants, especially of the spe- 

 cies which, so easily recognized by its tuberculate surface, appears to 

 be the most common one, and the more characteristic too of the Lig- 

 nitic. This is a proof that the eocenic character of this formation is 

 not limited to its base, and that the lower sandstone, together with the 

 beds of lignite, are of the same formation ; that, indeed, as it will be 

 seen elsewhere, the lower sandstone sometimes includes in its divis- 

 ions beds of lignite to its base.* 



Can we here determine the upper part or the end of this formation? 

 At the Eaton its lower stage is especially formed. I could see there 

 nothing in ascending the highest hills or slopes covering the volcanic 

 central group which indicated any change in the characters of the strata. 

 But near the center of the Lignitic of the Arkansas Yalley, the forma- 

 tion is covered with high hills, and the 200 feet of lignite-bearing meas- 

 ures above those marked in the section are overlaid by beds of coarse 

 grit, mostl}^ conglomerate sandstone, which I consider as the closing 

 strata of the Eocene-Lignitic period. For this, as for the great sand- 

 stone of the base, we have to see if these upper conglomerate strata 

 have been observed elsewhere and in circumstances which may prove 

 their immediate connection with the Lignitic. Here the 200 feet of 

 measures under them are formed by an alternance of beds of soft clay 

 or soapstone, with an abundance of silicified wood, beds of lignite, 

 (the outcrop of one near the top indicating at least two feet,) beds 

 of clay, which become hard, uninterrupted, blackened by carbonaceous 

 matter; and over them, in immediate superjiosition, ferruginous con- 

 glomerate sandstone separated by bands of soft-grained sand-rock in a 

 thickness of about 75 feet. No trace of organic remains are found in 

 this top sandstone. I found fucoidal plants mixed with broken remains 

 of Cyperaceiie as high as 300 feet below the top. 



Three miles northeast of Caiion City i had opportunity of examin- 

 ing the formation which underlies No. 1 of Mr. Clark's section. It is 

 a compound of thin beds of yellow, compact, sandy clay, separated by 

 thin layers of coarse materials or of sandstone. It contains animal 

 remains only, large scales of fishes and shells of Cretaceous characters 

 overlying the black shale No. 4, in a thickness of about 40 feet. What 

 there remains of this upper group of the Cretaceous is not much, the 

 materials being too soft, and having been swept away by erosion. But 

 there is enough left to show at once the great difference existing in the 

 compounds and nature of the strata of this Cretaceous upper formation, 

 and of those of the lignitic sandstone, which here is immediately aboye. 

 The superposition is seen, as remarked above, in the Arkansas Valley, 

 on the banks of a creek on the stage-road midway between Pueblo and 

 Caiion City. 



All this is not new. The same yellow, arenaceous clays of No. 5 in 

 the Arkansas Yalley are already exactly characterized and reported by 

 Dr. Hayden,t who marks, too, their succession in ascending as " passing 

 up into a somewhat extensive series of what 1 call mud-beds, composed 

 of thin layers of clay and mud sandstones, with aU kinds of mud-mark- 

 ings, sort of transition beds or beds of passage. In the upper portion 

 of these layers I found an imperfect specimen of Inoceramns. This 

 group of beds is from 50 to 100 feet in thickness. Resting upon them is 

 a thick bed of rusty-yellow sandstone, which I regard as the lower bed 

 of the Tertiary deposits," &c. These mud-beds, with all kinds of mud- 



* Dr. Hayden lias, from five miles south of Trinidad, specimens of the same plants 

 labeled, "From the sandstone above the coal." 

 t Dr. F. v. Hayden's Report, 1869, p. 50. 



