NATURAL SCIENCES OP PHILADELPHIA. Ill 



The Coal Measures, when thoroughly studied, will be found to hold an im- 

 portant position among the geological systems of the far West. According to the 

 investigations of Prof Shallow, they extend down the Missouri river to Lexing- 

 ton, and we may safely say that they occupy that portion of Kansas bordering 

 upon the river,'and for a considerable distance into the interior. We have 

 satisfactory evidence of their existence in the vicinity of Fort Laramie, and 

 also that they occupy a considerable area near Great Salt Lake, Utah Terri- 

 tory. 



Little is, however, known of the geology of these for western regions ; our 

 present information consisting for the most part of isolated facts. 



System II. — Cretaceous. 



This system holds a very important position in the North West not only 

 from the vast area which it occupies, but also in consequence of_ the 

 number, variety, and beauty of its organic remains. The different formations, 

 as they appear in ascending the Missouri, hare been separated into five 

 divisions, presenting generally well-marked lithological differences, and for 

 the most part characterized by different species of fossils. I shall first speak 

 of Formation No. 1 of the Vertical Section, presuming, however, that from all 

 the information yet obtained, its geological position is not definitely determined. 

 Thus far the weight of evidence seems to be in favor of its belonging to the 

 Cretaceous System. We will consider it provisionally, therefore, as the lowest 

 member of the Cretaceous System in this region, and as the first of the series of 

 beds of that age seen in ascending the Missouri. 



Formation No. 1 of Vertical Section* 



In the order of superposition, Formation No. 1 rests directly upon the true 

 limestones of the Coal Measures before referred to. Its first exposure seen 

 along the Missouri is at Wood's Bluffs, right bank, about eighty miles above 

 the mouth of the Platte, and it dips beneath the water level of the Missouri, 

 a few miles below the mouth of the Vermilion. Its general character is a 

 coarse grained, friable sandstone, very ferruginous, of a yellow or reddish 

 yellow color, with thin beds of impure lignite aud various colored claj-. It con- 

 tains very few fossils, mostly of the genera Solm, Cyprina and Peclitnculm, also 

 fossil wood, and numerous impressions of dicotyledonous leaves, similar to the 

 common willow. Its entire thickness is estimated at ninety to one hundred 

 feet, but it may be more. The relation which I suppose this formation holds 

 to one of a similar character near the mouth of the Judith river will be noticed 

 hereafter. 



Formation No. 2 of Vertical Section. 



This Formation is first revealed in thin outliers below the mouth of Big 

 Sioux river, and on that stream six miles above its mouth it caps the Bluffs, 

 apparently mingling to some extent with the succeeding bed, and containing 

 at this locality large numbers of Inoceramus problemaiicus and fragments of 

 fishes. Near the mouth of Iowa creek and above, it shows itself worthy of 

 a separate position in the series. It is composed of a dark leaden gray laminated 

 plastic clay, containing few fossils, but great quantities of the sulphate of lime in 

 crystals, assuming a variety of beautiful forms. Its greatest thickness is 

 seen five miles below the mouth of James river. At Dorion's Hills it is seen 

 at low water mark. Entire thickness estimated at ninety feet. Fossils, 

 Ammonites, Inoceramus, Cytheria, Serpula, Oslrea and abundant fish remains. 



Formation No, 3 of Vertical Section. 

 The geographical distribution of this formation and its influence on the 

 scenerj- render it one of the most interesting on the Missouri. It is first seen 

 in thin outliers near the mouth of Big Sioux river, and becomes quite con- 



* See Vertical Section in a paper by F. B. Meek and F. V. Hayden, in 

 this number of the Proceedings of the Academy. 



1857.] 



