420 N. H. DARTON PALEOZOIC AND MESOZOIC OF ^VYOMING 



known natural bridge. This sandstone is massive, coarse-grained, and 

 usualh' of light gray color, but in some of the ridges west of Douglas it is 

 dark gray to brown on weathered surfaces. At Beaver it underlies a 

 l)road synclinal valley mostly filled with Chadron and Brule formations. 

 On La Bonte creek, a mile northwest of Springhill, the formation is about 

 700 feet thick and includes sandstone, red shale, and cherty beds in the 

 lower portion. At the base, under 20 feet of limestone, is a 3-inch bed 

 of conglomerate lying on 15 to 30 feet of disintegrated granite. On 

 3Iuddy creek, where the basal sandstone is thin and either locally absent 

 or faulted out, the limestones are 300 feet thick and the top sandstone 

 nearly 100 feet thick. 



Bates creek to Syhille creek. — About 3 miles northeast of Freeland the 

 Casper limestone bends around the northwest point of the general anti- 

 cline of Laramie mountains and trends southeastward to Laramie river 

 and beyond. It rises mostly in a line of monoclinal foothills, but a short 

 distance north of Laramie river it is deflected westward by two promi- 

 nent anticlines extending out of the Laramie mountains. The formation 

 is mostly limestone 200 feet or more thick lying on a small amount of 

 sandstone and overlain by gray sandstone (Tensleep). At an exposure 

 5 miles north-northwest of Marshall 100 feet of the lower beds of the 

 limestone contain nimierous cherty layers and are separated from the 

 granite by 30 feet or more of red shale merging down into a foot or two of 

 sandstone. This red shale strongly suggests the basal member of the 

 Amsden formation. Near Marshall the basal sandstone is only a few 

 feet thick, but brown and hard. The limestone here is only 200 feet 

 thick. From this region to a point west of Garrett the upper sandstone 

 member becomes conspicuous, with a thickness of 100 feet and the charac- 

 ter of the Tensleep sandstone. It is quartzitic and rises in prominent 

 knolls. It also appears at intervals south to Syhille creek, but is thinner, 

 becomes reddish in color, and in places carries intercalated limestone. 

 Xear Sj'bille creek the base of the formation is faulted out for some dis- 

 tance, so that only 80 feet of limestone remain ; but farther south the 

 limestone is seen to be 250 feet thick and separated from the granite by 

 20 feet of pink sandstone. I believe that from Casper mountain south- 

 ward the basal sandstone is a shore deposit of the Casper formation lying 

 on a sloping shore of pre-Cambrian rocks and rising progressively higher 

 in the formation to the south. 



Shirley-Freezeout uplifts. — Carboniferous and associated rocks appear 

 around the southern and eastern ends of the Shirley hills and in the 

 southern part of the Freezeout hills, but in the greater part if not all of 

 the area thev can be divided into several formations. There are three 



