GEOLOGIC RELATIONS OF LARAMIE OF DENVER BASIN. 



85 



He wrote as follows concerning the stratig- 

 raphy and paleontology: 



In this valley, as in all the plains region round about, 

 the exposures of strata are not only few, but none of them 

 are extensive. The most southerly exposure is about 10 

 miles from the mouth of the creek, and here I again rec- 

 ognized the oyster horizon, which has been mentioned 

 twice 1 before. The species mentioned before were found 

 abundantly here, and many other molluscan species 

 besides, in associated layers. I traced this fossiliferous 

 horizon northward for a distance of 5 or 6 miles above the 

 point where I first discovered it and found it to occupy 

 nearly a uniform height above the level of the creek. 

 The exposures are in the face of the low sloping hills that 

 border the east side of the valley and are distant from the 

 creek only from a few hundred feet to half a mile. 



The full section of the strata constituting the valley 

 side here was quite clearly ascertained, although the 

 debris which prevails upon the plains has so obscured them 

 in most places, even on the slope, that they were not 

 all observable at any one point. The following is a 

 record of the section as ascertained by, measurements at 

 several different points within the few miles that they 

 were found exposed, as before stated: 



Crow Creek section. 



Feet. 



1 . Sandy soil or debris of the plains 10 



2. Grayish siliceous marl 5 



3. Sandy and calcareous layers; with Corbula, 



etc 3 



4. Soft sandy and argillaceous material; with 



Ostrea and Anomia 5 



5. Arenaceous rock, somewhat concretionary; 



with numerous fresh- water forms 2 



6. Arenaceous marly strata 20 



7. Carbonaceous shale; 6 



8. Gray siliceous marl 6 



9. Carbonaceous shale 3 



10. Gray siliceous marl 25 



11 . Unexposed to the surface of the creek 5 



No. 1 is the prevailing d6bris of the plains, which at top 

 constitutes the sandy soil. 



No fossils were found in No. 2, but it is evidently a 

 part of a continuous deposit with those beneath. * * * 



The following is a list of the fossils obtained from the 

 different members of this section: 



List of fossils from the valley of Crow Creek, Colo. 



1. Anomia micronema Meek. 



2. Anomia gryphorhynchus Meek. 



3. Ostrea glabra Meek and Hayden. 



4. Volsella (Brachydontes) regularis White. 



5. Anodonta parallela White. 



6. Unio ? 



7. Corbicula cleburni White. 



8. Corbicula obesa White. 



9. Corbicula cardiniaeformis White. 



10. Corbicula (Leptesthes) subelliptica Meek and 



Hayden. 



11. Corbicula (Leptesthes) fracta Meek. 



12. Corbicula (Leptesthes) macropistha White. 



List of fossels from the valley of Crow Creek, CoZo.— Contd. 



, 13. Corbicula (Leptesthes) planumbona Meek 



14. Corbula subtrigonalis Meek and Hayden. 



15. Bulinus disjunctus White. 



16. Bulinus subelongatus Meek and Hayden. 



17. Physa felix White. 



18. Goniobasis gracilienta Meek and Hayden. 



19. Goniobasis nebrascensis Meek and Hayden. 



20. Melania wyomingensis Meek. 



21. Viviparus prudentia White. 



22. Tulotoma thompsohi White. 



23. Campeloma multistriata Meek and Hayden. 



24. Corydalites fecundum Scudder. 



# * * * * * * 



At a point about 18 miles east of Greeley I found the 

 uppermost strata of the Fox Hills group in the south 

 valley side of South Platte River, and from that point to 

 about 6 miles farther eastward I continued to see small 

 exposures of the same, most of which were obscure. I 

 however recognized about 20 feet in thickness of strata, 

 and the fossils, which were few and imperfect, were quite 

 sufficient to indicate an exact equivalency of the strata 

 containing them with those of the upper part of the sec- 

 tion at the mouth of the St. Vrains. Besides these few 

 characteristic invertebrate fossils, I also found fragments 

 of the fucoid Halymenites major in one of the upper layers. 

 The known general dip of the strata of all that region 

 makes it practically certain that the Cretaceous strata pass 

 beneath the level of the streams along a northward and 

 southward line which may be drawn a couple 6f miles 

 west of Greeley; that they receive a greater or less thick- 

 ness of Laramie strata upon them beneath the debris Of 

 the plains. Then a gentle rise brings them up again to 

 view in the valley of South Platte River, from 18 to 25 

 miles east of Greeley, as already mentioned; They seem 

 then to pass again by a gentle easterly dip beneath the 

 surface of the river, but I did not trace them farther, as 

 my journey led up the valley of Bijou Creek. It is prob- 

 able, however, that the exposures of these uppermost of 

 the Fox Hills strata continue at the surface farther down 

 the South Platte, in its immediate valley. Between 

 Greeley and the point where these Cretaceous strata are 

 exposed the space is ho doubt occupied by at least a small 

 portion of the strata of the Laramie group, which are 

 covered with the ddbris of the plains, but I found no 

 exposures of Laramie strata until I reached the valley of 

 Bijou Creek, about 12 miles above its mouth. * * * 



From the valley of Bijou Creek my investigations led 

 me southwestward to Cherry Creek Plateau, during which 

 I passed over the higher strata of the Laramie group, 

 which come in the series between those that I found 

 exposed near Bijou Station and the sandstones of the 

 Monument Creek group that constitute the plateau. I 

 found no fossils of any kind in these higher Laramie st r ata 

 except silicified wood, which in some places was quite 

 plentiful. It is possible that certain layers in this por- 

 tion of the Laramie group contain invertebrate fossils, but 

 the whole series in this region above the horizon of the 

 fossiliferous layers of the Crow Creek and Bijou Creek 

 sections is apparently destitute of invertebrate remains. 



■ The whole thickness of Laramie strata which I thus 

 passed over, from the uppermost layers of the Fox Hills 



