BASE OF THE LARAMIE. 151 



orado, have been described by Dr C. A. White.* Some of the fossils 

 obtained there also occur in the Denver beds, in the Ceratops beds of 

 Converse county, and at Black Buttes, and it has been suggested that 

 possibly the Denver or Arapahoe beds, as well as the Laramie, might be 

 represented there. We found fairly good exposures near the Canfield 

 ranch and four or five miles above it, in the neighborhood of a large 

 irrigation reservoir. Fossils were distributed through the 40 or 50 feet 

 of beds exposed, and they are associated throughout in such a way as 

 to remove all doubt as to the unity of the formation, which is certainly 

 of Laramie age. This conclusion received additional confirmation from 

 a few species of plants found at the base and near the top of the exposure. 



General Considerations. 



base of the laramie. 



The facts stated in the preceding pages have an important bearing on 

 the more general question as to the upper and lower limits of the Lara- 

 mie. King's original definition of the Laramie t as the coal-bearing 

 series that conformably overlies the Fox Hills beds is a simple one, but 

 its practical application in the field is often a difficult matter, especially 

 in areas where there have been alternations of marine deposits with tfyose 

 of fresh or brackish waters in which conditions were favorable for the 

 formation of coal. In speaking of such alternations in Montana, Hatcher X 

 concludes that — 



" The terms Fox Hills and Laramie as now used cannot be taken to represent 

 distinct and different periods of time. . . . Marine beds with typical Fox 

 Hills fossils have been found interstratified with fresh and brackish water beds 

 containing characteristic Laramie fossils, showing conclusively that the two periods 

 were, in part at least, contemporaneous." 



If this view be adopted, then the term Laramie has no time significance 

 whatever, but simply indicates the conditions under which sedimenta- 

 tion occurred at different times. In western Colorado, Hills met with the 

 same difficulty, but solved it in a different way. He says : § 



" For economic reasons, we could wish that the base of the Laramie were made 

 to coincide with the base of the productive coal measures or, what amounts to the 

 same thing, with the lowest strata containing land plants. It may be well to ex- 

 plain, however, that the base of the productive measures does not always include 

 the lowest coal seams exposed. . . . For the present, therefore, as in a former dis- 

 cussion of this question, I shall regard the base of the Laramie as limited by the base 



*Ann. Rep. U. S. Geol. Survey Terr, for 1877, pp. 163-174. 



|U. S. Geol. Expl. 40th Parallel, vol. i, pp. 298, 331. 



I American Naturalist, vol. xxx, p. 117, Feb., 1896. 



I Proc. Colo. Scientific Society, vol. iii, pt. iii, 1890, p. 382. 



XXII— Bull. Geol. Soc. Am., Vol. 8, 1896 



