THE EOCENE OF NORTH AMERICA 45 I 



as "calcareous sands and slightly siliceous limestones, which 

 are overlaid by remarkably fissile shales." The limestones are 

 about 800 feet thick; the shales 1200 feet thick. The beds 

 contain fresh-water fossils but " no brackish-water forms what- 

 ever." * 



The formation of the Bridger substage is described by King* 

 as follows : "Throughout the middle of the Bridger Basin it 

 rests in positions of complete horizontality, and throughout its 

 whole extent shows no evidence of orographical disturbance, 

 such as could be registered in local changes of angle. The 

 aggregate thickness of the beds of this group is estimated as 

 between 2200 and 2500 feet. The material is almost wholly 

 made up of fine sand and clay, arranged in varying proportions 

 and occasionally slightly changed by calcareous mixtures." Scott 

 correlates the Bridger with the Parisien of Europe. 3 



THE HUERFANO FORMATION 



The Huerfano beds in Huerfano county, Colorado, were first 

 described by R. C. Hills in 1888. He estimated the thickness 

 to be 8000 feet and made three divisions of the beds. In 1891 

 Hills identified the upper beds, which consist of clays, soft shales 

 and sand, as Bridger, and estimated its thickness at 3300 feet. 

 Below this lie the Cuchara beds 300 feet thick, and below the 

 Cuchara are the Poison Canyon beds 3500 feet thick. The lower 

 two divisions he considered Lower Eocene. In 1897 Osborn and 

 Wortman visited the region and arrived at the following conclu- 

 sions 4 : (1) "That west of Huerfano Canyon the variegated marls, 

 clays, soft shales and sands aggregate only 800 to 1000 feet in 

 thickness and are nearly horizontal in position. They may be 

 positively divided into upper beds equivalent to the Bridger, 5 

 and lower beds, equivalent to the Wind River or Upper Wasatch. 



'King: loc. cit.. p. 389. 2 Loc. cit., p. 400. 



3 Science, n. s., Vol. II, p. 499, 1895. 



* Osborn : Bull. Amer. Mus. Nat. Hist., Vol. IX, p. 250, 1897. 



5 "Bridger" and " Wind River" appear to be used in the sense of "Bridger 

 substage" and " Wind River substage" respectively as used by Scott. Cf. Scott's 

 Introduction to Geology, p. 496, table. 



