white.] LAEAMIE FOSSILS OF YAMPA VALLEY. 207 



are very valuable for general application, the known great vertical range 

 of some of the species makes it impracticable to place implicit reliance 

 upon any single species as indicating a definite limited horizon within 

 the group. The following comparisons and references will show how far 

 the paleontological indications agree with the known stratigraphical 

 position of the fossils in question. According to our present knowledge 

 of the range of the species of the Fox Hills Group, the presence of 

 SeapMtes nodosvs among these fossils indicates for them a low horizon in 

 the Fox Hills Group, as does also Thetis f circularise if that species has 

 been correctly identified. 



On the other hand, all the others may be regarded as ranging through 

 the whole upper half of the Fox Hills Group in Colorado, and some of 

 them below if, including Baculites ovatus, which, as before stated, ranges 

 higher upon the west side of the Rocky Mountains than it is known to 

 do upon the east side. Besides this, Inoceramus pertenuis, which is 

 doubtfully identified here, is a species hitherto known only in the upper- 

 most strata of the Fox Hills Group in the Upper Missouri Elver region; 

 and a variety of I. baraMni also exists in the same strata. Summing 

 up the whole paleontological evidence then, it is seen that while it is 

 suggestive of a lower horizon, there is nothing to prove that the strata 

 containing these fossils may not really belong, as they appear to do, to 

 the uppermost portion of the Fox Hills Group. Therefore we need not 

 assume that the strata of the last named group were in any degree re- 

 moved by erosion in this neighborhood before the deposition of the 

 Laramie strata. Careful examination at the junction of the two groups 

 in the neighboring hillsides also failed to discover any plane of demark- 

 ation between them. This fact has the same general application in this 

 region west of the mountains that it was found to have at their eastern 

 base. 



No other fossiliferous horizons were found in this neighborhood, either 

 in the Fox Hills or Laramie Groups. My journey led me down the val- 

 ley of the Yampa, dining which 1 passed much of the way over Laramie 

 strata, as determined by their stratigraphical position and character- 

 istics, as far down as opposite the confluence of Williams Elver before 

 I found any fossils to confirm those previous conclusions. From this point 

 to one about seven miles below, in the north valley side of the Yampa, 

 I found somewhat frequent exposures of fossiliferous layers, the prin- 

 cipal of which was found in Canon Park, a portion of Yampa Valley. 

 The fossils collected here will be treated as from one locality, because 

 they are practically upon one horizon and essentially the same species 

 of fossils occur at each locality, except two or three limited ones, where 

 no others besides the Ostrea were found. 



LIST OF LARAMIE FOSSILS COLLECTED IN YAMPA VALLEY, NEAR 

 CANON PARK, NORTHWESTERN COLORADO. 



1. Ostrea glabra Meek & Hayden. 



2. Anomia micronema Meek. 



3. Anomia grypJwrhynchus Meek. 



4. Yolsella (Brachydontes) regularis White. 



5. Corbicula occidentalis Meek & Hayden. 



6. Corbicula (Leptesthes) pacta Meek. 



7. Corbula subtrigonalis Meek & Hayden. 



8. Neritina volvilineata White. 



9. Melania wyomingensis Meek. 



10. Viviparus plicapressus White. 



11. Campeloma multistriata Meek & Hayden. 



