176 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



Fossil liidge I passed up to Spring Cauoii, andtlience through a i)ortioii 

 of it among the foot-hills. Some minor hills that lie immediately adja- 

 cent to the foot-hills proper are formed of the hardened shales and 

 calcareous layers of the lower portion of the Colorado Group; but 

 the principal foot-hills are mostly in the form of hogbacks that were 

 produced by the upturning of the strata of the Dakota Group and the 

 Eed Beds. 



I prosecuted a labored but unsuccessful search for fossils in the strata 

 of these hogbacks, as 1 did, also, in those of Box Ekler Canon, which is 

 a similar gorge, througli these same strata, similarly upturned. From 

 their stratigraphical characteristics and relative position the Eed Beds 

 were easily recognized as those that have been generally regarded as of 

 Triassic age, and the strata of the Dakota Group were just as readily 

 identified, although no fossils were discovered. There is also a series of 

 strata between these two groups, wliich, being softer than the others, 

 has yielded more to disintegration. These were recognized and described 

 by the late Mr. Marvine, in his report, as Jurassic strata. In this he 

 was probably correct, but so far as I am aware no invertebrate fossils * 

 of any kind have been found in these strata or in their equivalents east 

 of the Eocky Mountains in Colorado, except a shell found by Mr. Lakes 

 and noticed in connection with fossils found in the vicinity of Golden 

 City, on a following page. 



Eeturning to Fossil Eidge I made considerable collections of fossils 

 there, a part of the species being very abundant. They were obtained 

 mainly from " cannon-ball" concretions, some of which are very large 

 and which were weathered out of softer layers of sandstone. It has 

 already been mentioned that a part of these fossils are of the same spe- 

 cies that characterize the Fort Pierre Group of the Upper Missouri Eiver 

 region. It is a well-known fact that several species of fossils are com- 

 mon alike to both the Fort Pierre and Fox Hills Grouj)s, even in the 

 region just mentioned, and this is so especially the case in Colorado 

 that no attempt is made to separate them, and I have in my report 

 of last year ranged the equivalents of both groups under the single 

 name of Fox Hills Group, and shall do so in this report. It is neverthe- 

 less true that a greater i^roportion of the species found in the lower part of 

 the Fox Hills Group, as thus recognized in Colorado, are identical with 

 those of the Fort Pierre Group than with those of the Fox Hills Group, 

 as those two groups are recognized in the Upper Missouri Eiver region. 

 Tliis fact is apparent in the strata exposed in Fossil Eidge, as is shown 

 in the following list of fossils : 



ISTot only this fact, but also the known dip to the eastward, which 

 brings up lower and lower strata toward the foot-hills, indicates that 

 those at Fossil Eidge belong to a lower horizon than those which I 

 examined in the valley of the Cache a la Poudre. 



LIST OF CEETACEOUS FOSSILS COLLECTED AT FOSSIL EIDGE, THREE 

 MILES SOUTHEASTWAED FEOM SPEINO CANON, AND ABOUT SIX 

 MILES SOUTH OF FOET COLLINS, COLOEADO. 



1. Ostrea patina Meek & Hayden ? 



2. Pinna laliesi White. 



3. Fteria Unguiformis Evans & Shumard. 



* Some remarkable Dinosairriau remains have been obtained from the iipiser strata 

 of this group at the toAvn of Morrison, on Bear Creek, Colorado. See address of Prof. 

 O. C. Marsh, Proc. Am. Assoc. Adv. Sci. vol. xxvi, pp. 22 et seq. See also fiirtlier 

 remarks on a following page. 



