CRETACEOUS SYSTEit 449 



to 1 inch in diameter, partly of jasper. This merges up into a coarse 

 Imff sandstone, followed b}' 60 feet of shales, mostl}' dark, l)nt in part of 

 purplish red color, and then tlie top sandstone. In places tlierc are two 

 sandstone members besides the basal one, separated by shale. The upper 

 sandstone is thin-l)edded and rusty in color. Sonth of l)onglas there are 

 three 'sandstones, the basal one coarse-grained and conglomeratic as on 

 Muddy creek. Locally the npper sandstone l^ecomes especially prominent 

 and is imderlain by 20 feet or more of reddish clay. About Alcova the 

 formation is about 50 feet thick and consists of dark conglomerate below 

 and white or bnff sandstone above. Near the south end of Platte canyon, 

 .35 miles above Alcova, where the thickness is 60 feet, the basal portion 

 is massive conglomerate containing numerous boulders up to 6 inches 

 in diameter, including many of limestone, apparently Carboniferous. 

 Como ridge east of Medicine Bow is capped by Cleverly sandstone, and 

 this rock circles aroimd the end of Preezeout uplift and the anticline 

 north of Medicine Bow and rises in a prominent monoclinal ridge on the 

 east side of Little Medicine valley. Here the thickness varies from 125 

 to 150 feet, and in the high butte on the axis of the anticline, 15 miles 

 northeast of Medicine Bow, there are. two sandstone members separated 

 by gray and purplish shale and clay. West of Marshall, where the thick- 

 ness is less, the formation appears to consist entirely of hard, gray sand- 

 stone. 



Laramie basin. — In Laramie basin the Cloverly is seldom more than 

 200 feet thick and ordinarily the amount is considerably less. As in other 

 regions, it consists of two sandstone members separated by buff and 

 purplish, sandy clays. The sandstones, especially the lower ones, arc 

 usually locally conglomeratic, with pebbles of vari-colored cherts and 

 jasper. The lower sandstone is the most prominent member topograph) c- 

 allj, often giving rise to a prominent hogback ridge. At the north end 

 of the hogback at the east end of Centennial valley the formation con- 

 sists of 10 feet of massive sandstone, 100 feet of flaggy, ferruginous sand- 

 stone and shale, and at the base 40 feet of massive, wliite sandstone. 

 The latter is conglomeratic in places and lies on 30 feet of ferruginous 

 shales which may belong either in the Cloverly or Morrison formations. 

 Below are 300 feet of typical, bluish to purple, Morrison shales. On the 

 south bank of Laramie river, north of Jehn mountain, the formation 

 consists of 25 feet or more of buff, flaggy sandstone, then 60 feet of 

 shales, greenish above, buff beloAV, Avith some layers of flaggy, white sand- 

 stone, and, at the base, 23 feet of flaggy, buff sandstone. In llie auli- 

 cline on the south side of Hutton lake, 10 miles southwest of Laraniic. a 

 complete section of vertical beds is exposed as follows: 



