GEOLOGY AND MINERALOGY. 323 



This exposure presented the following beds in the descending order : 



let. 20 feet exposed of light gray limestone and marl, con- ) No. 3 of 



taining Tnoceramus problematicuSs ) Nebraska Sec. 



2nd. 45 feet dark laminated clay with ferruginous concre- 1 No. 2 of 



tions containing fish scale. > Nebraska Sec. 



3rd. 15 feet exposed above the edge of the water, consisting ■^ 



of yellowish friable sandstone, with a thin bed of impure f ^'^' ■'■ ^^ 

 lignite above, and some layers of various colored clay C Nebraska Sect, 

 below, containing dicotyledonous leaves. J 



One of the sketches of a long lanceolate leaf, like some of the existing species of 

 Salix, sent by us to Prof. Heer, was drawn from a specimen collected from one of 

 the lower sandstones here. 



Again at another locality on the Missouri, about thiity miles above the mouth of 

 Big Sioux river, No. 1. was seen by one of us (Dr. H.) only five feet above the 

 water's -edge, and immediately overlaid by No. 2, of the Nebraska section, contain- 

 ing its characteristic species of Ammonites : and directly over the latter, he saw 

 Ifo. 3, containing Inoceramus Problematicus,* At this locality he also found in 

 No. 1, some of the same fossil leaves characterizing it at the other places already 

 mentioned. 



In ascending the Missouri, the last above named locality, formations Nos. 2, 3, 

 4 and 5 are seen to sink at the same gradual uniform rate of dip, in regular suc- 

 cession, beneath the level of the Missouri ; so that on reaching Heart river, we 

 find the top of No. 5 nearly down on a level with the water's edge, and a short 

 distance above that locality it passes out of sight, to be succeeded by the Great 

 Tertiary Lignite basin of the upper Missoui'i, which overlaps it on the hills along 

 the river for some distance below. 



From the foregoing statement, we think it will be clearly understood, that form- 

 ation No. 1 of the Nebraska section holds a position beneath the other cretaceous 

 deposits of that region ; while the occurrence in it of highly organized angiosperm 

 dicotyledonous plants proves that it cannot be older than Cretaceous. It may be 

 argued, however, that it may in part be Cretaceous, and part Tertiary, or at any 

 rate that sojne of these leaves may have been obtained from overlying Tertiary 

 beds which we have confounded with the Cretaceous below. This, however, is 

 impossible, simply because specimens of nearly all the species found at the various 

 localities, have been quarried ftom the same bed at Blackbird Hill, and the whole 

 — not a part only of this formation — passes beneath all the other Cretaceous rocks 

 of the North west. In addition to this, we have extensive collections of plants 

 from the Tertiary of Nebraska, not a single species of which is identical with 

 those from No. 1. 



When we stated in some of our papers that it was possible we might have in- 

 cluded in this formation beds not belonging to the Cretaceous, it was not because 

 we thought any pai't of it might be Tertiary, but because we suspected some of the 



* It is of course unnecessary for us to inform geological readers that a rock overJaid by 

 strata containing Ammonites and Inoceramus cannot be Tertiary, because these gpnera 

 became extinct at the dawn of the Tertiary epoch. 



