CRETACEOUS SYSTEM 447 



Freezeout hills (bed number 22 on page 44-i) ]\Ir Logan reports Unio 

 l-nigliti. U. wilUstoni, U^. haileyi, Vol rata Icei. and Pla)iorhis vcternu^i. 

 'J'he two latter also occnr in l)ed number 21. iS[\imero\is eycads and fossil 

 wood, together with a fragment of a liollow-boned dinosaur, arc reported 

 from bed 18 in the same section. 



The dinosaur remains in the Morrison have been regarded as Jurassic, 

 but some paleontologists believe that they are early Cretaceous. As tlic 

 stratigraphic relations in some regions sustain this latter view, the forma- 

 tion is provisionally assigned to the Cretaceous. 



CLOYERLY SANDSTONE 



Occurrence mid general character. — The Cloverly sandstone, at one 

 time called the "Dakota sandstone," extends continuously through central 

 Wyoming, usually giving rise to a liogback range on the slopes of the 

 various uplifts (see plates 28 and 29). The outcrops extend along the 

 sides of the Owl Creek and Bridger uplifts and the northeast side of tlic 

 Wind Eiver range, but in places it is covered by Tertiary. It appears 

 again in the anticline extending from Dallas to beyond Fort Washakie ; 

 also on Conant and Muskrat creeks and along the north side of the Rat- 

 tlesnake uplift, where it extends nearly to Oil City. It outcrops exten- 

 sively about Alcova, along both sides of the uplift of the Freezeout hills, 

 in the region southwest and south of Casper and Douglas, in the uplifts 

 north and east of Medicine Bow, along the east side and south end of 

 Laramie basin, in Centennial valley, and on the east side of Laramie 

 mountains from Chngwater creek to Middle fork of Crow creek. A small 

 outlier remains in the syncline near Jelm post-office. The principal rock 

 is hard, coarse sandstone, nearly everywhere in two members, separated hy 

 gray and purplish clay. The lower sandstone is generally conglomeratic, 

 at least in its lower portion. The formation averages 150 feet thick and 

 lies on Morrison formation, with an erosional unconformity that is usual 

 when coarse sandstone or conglomerate lies on shale or clay. 



Owl Creeh mountain^:. — In the Owl Creek Mountain uplift the thick- 

 ness of the Cloverly formation ranges from 100 to 150 feet. The outcrop 

 zone extends for many miles along the north side of tlic mountains and 

 along their south side from the headwaters of iSTorth fork of Muddy creek 

 to the Tertiary overlap south of Black mountain. Small exposures ap- 

 pear on the south side of the mountains, near longitude 108° 30', ami 

 more extensive ones encircle the uplifts between Muddy and Dry creeks, 

 near longitude 109°, and the anticline wliich passes through Thermopolis. 

 There is a lower member of hard, coarse, gray to buff sandstone in mas- 

 sive beds and an upper member of massive shale of purplish color contain- 



