THE COLORADO FORMATION AND ITS INVERTE 



MATE FAUNA. 



By T. W. Stanton. 



INTRODUCTION. 

 HISTORY AND DEFINITION OF THE COLORADO FORMATION. 



For many years the well-known upper Missouri section has served as 

 the basis for all studies in the Cretaceous formations of the great in- 

 terior region of the United States. As first published in 1856, by Hall 

 and Meek, 1 and with a few slight modifications, by Meek and Hayden, 2 

 it embodied the notes on the Cretaceous strata made by the two authors 

 last named during the earliest of their geological reconnoissances in 

 the upper Missouri river region. It has since been modified and en- 

 larged from time to time by the same authors and by others, and made 

 to include, more or less successfully, all the Upper Cretaceous strata 

 in the region from Kansas to Arizona and from southern New Mexico 

 far northward into British America. 



In its original form this upper Missouri section was divided into five 

 parts, which were simply designated by numbers, beginning at the base. 

 The total thickness of the entire Cretaceous series of that region was 

 at first estimated at not more than 650 feet. In 1861 Messrs. Meek and 

 Hayden 3 published a paper in which names were given to the five divi- 

 sions, with the addition of lists of characteristic fossils and references to 

 typical localities. It should be remembered that this is not a contin- 

 uous section at any one locality, but it is generalized from all the out- 

 crops seen over a very large area. The thickness assigned to each 

 group is an estimate of its maximum development. The section, as 

 republished in 1876 by Meek, 4 who made no changes excepting in the 

 nomenclature of a few of the fossils, is as follows: 



* Mem. Am. Acad. Arts, and Sci.. 2d ser., vol. V, p. 405. 

 2 Proc. Acad. Nat. Sci. Phila., vol. vm, p. 03. 



» Proc. Acad. Nat. Sci. Phila., 1801, p. 419. 



• U. S. Geol. Sur- of the Territories, vol. ix, pp. xxiv and xxv. 



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