BEBLKHJKAPHY. 11 



more than a historical interest. Hitchcock's map went through several editions 

 without change; Marcou's was republished a number of times and frecjuently altered. 

 Perhaps its best form is that which accompanied his (xeology of Noi'th America in 

 1868. These maps were the precursors of a numbei' of similar attempts which have 

 appeared from time to time and which for the present cuhninate in the McCJee map, 

 the latest and so far the best general geologic map of the United States. Maps of 

 this sort form a rather distinct but small and relatively unimportant branch of the 

 literature relating to the geology of Colorado, and 1 have made no determined effort 

 to include all of them in my bibliography. The scale to which thej' are drawn and 

 the unequal character of the information upon which the}^ are based, brought 

 together from a variety of sources, do not permit the eras to be so subdivided or the 

 divisions so represented upon the map as to be serviceable for detailed comparisons. 

 The}^ can not present the facts in the detail of the original reports which furnished 

 them and which form the natural material for a bibliography. J. Marcou and J. B. 

 Mai-cou" and C. H. Hitchcock* have published descriptions of the general geologic 

 maps of the United States. 



The earliest account of actual geologic exploration in Colorado is that published 

 by Schiel in 1861. Schiel traversed a large tract of country very hastily, one 

 would judge, and his brief account, which in the light of later explorations contains 

 nothing of geologic importance, is of only historic interest. He entered the moun- 

 tains by the way of the Huerfano River, crossed the Sangre de Cristo Range, 

 traversed the south-central part of the State, and passed on to Salt Lake through 

 the San Juan and Wasatch mountains. He describes the lithologic character of both 

 sedimentary and igneous rocks traversed on this route, which was not one best 

 suited to display the Paleozoics of Colorado, but obtained no fossils from the older 

 rocks of the State, and only in one iTistance attempted to assign any of them to a 

 definite geologic period. In the Sangre de Cristo Valley he mentions as Cambrian 

 (p. 123) a bluish brittle limestone associated with hard shale and sandstone. 



This is clearly not Cambrian, and if not one of the Carboniferous limestones is 

 more probably of Cretaceous or Tertiary age. It would be possible, though cer- 

 tainly unprofitable, by careful comparisons of lithologic character and geologic 

 position, and with the aid of the maps and descriptions of later geologic work, to 

 determine the formations to which manj' of the beds mentioned by Schiel probably 

 belong, biTt it has not been attempted. This report was republished in its original 

 form the year following (1855). 



The account of the geology of the Upper Missouri, published by Hayden in 

 1863, though no longer of practical value, on account of more accurate work in the 



aV. S. Geol. Survey, Bull. No. V, 1884. bAra. Inst. Min. Eng., Trans., vol. 15, 1887, pp. 465-488. 



