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fessor Capcllini agree in regarding this sandstone in which the dicotyle- 

 donous leaves are found as a fresh-water formation. I would simply say 

 that I have always regarded it as marine, and I am sure this has been 

 the opinion of my friend Mr. Meek. At any rate, we have found mingled 

 with the leaves at Sioux City quite well preserved casts of Pharella dako- 

 tensis, Axinca siouxensis, and Cyprina arenacea, shells peculiar to marine de- 

 posits." Since that time a number of species of marine mollusks have been 

 found in the strata of this group, and Dr. Mudge, in his paper quoted above 

 from Transactions Kansas Agricultural Report, p. 396, gives a list of species 

 determined by Prof. B. F. Meek, all referable to marine mollusks : Crassatel- 

 lina oblonga, Area parallela, Yoldia microdonta, Cardium Icansasensis, C. sali- 

 nens,Cyrena {Corbiculd) nucalis, C. subtrigonalis, Tellina subscitirfa, T. mactroides, 

 Leptosolen conradi, Turritclla htnsasensis, Turbo mudgcanm. Professor Mudge 

 remarks on these shells that : " They are in the same strata and in the vicinity 

 of several deposits with the dicotyledonous leaves, and together with the 

 plants, identify this portion of the sandstone as belonging to the Dakota group 

 of the Cretaceous, as described by Messrs. Meek and Hayden, in their first 

 report.'" 



The opinion that this group of the Cretaceous may be a fresh-water for- 

 mation is, moreover, contradicted by its extent and by the homogeneousness 

 of its compounds. It has been seen that at some places it covers an area of 

 more than sixty miles in width, and that its length along the borders of the 

 Carboniferous or Permian measures is recognized as continuous from Texas 

 to the northern limits of Minnesota, thus passing through fourteen degrees of 

 latitude, even probably across the English portion of North America to Green- 

 land. It is not possible to suppose a fresh-water formation of such extent, 

 especially when we consider, as stated above, the homogeneity of the materials 

 composing it. For, indeed, with the exception of thin local strata of carbonace- 

 ous shale and soft clay, especially observed near its base, the compound is es- 

 sentially the same in the whole thickness and in the whole extent, varying 

 only in degree of hardness, compactness, and red coloring, resulting from the 

 different proportion of oxid of iron with which it is impregnated. This forma- 

 tion, by the character of its ferruginous arenaceous shale, even by its color, 

 and also by the special character of its flora, has the greatest analogy with the 

 red sandstones so widely formed at the end of the Devonian epoch, between 

 the Chemung and the Carboniferous, either as the Catskill group, or as the 



