26 GEOLOGICAL SURVEY OF THE TERRITORIES. 



of sandstone of all sizes from a few inches in diameter to several feet, 

 which split horizontally into thin laminae. The indurated sandy clay 

 in which these concretions are inclosed exhibits the same concretionary, 

 character so that the rocks weather into curiously fantastic forms. This 

 bed is undoubtedly cretaceous, and is probably a bed of passage to the 

 lignite tertiary. A few fossils are found in the harder masses, as Inocer- 

 amus, Baculites, &c. Above this bed is a thick group of grayish-brown 

 sandstones, with rusty brown concretions, which also weather into curi- 

 ous architectural forms. These benches extend nearly to the foot of the 

 upheaved ridge, with only a slight inclination, perhaps 5°. The older 

 beds are exposed forming a very narrow belt. 



Our camp on the night of August 21 was near the mouth of Muddy 

 Creek, on the North Platte, thirty-four and one-fourth miles northeast 

 of Fort Fetterman. Muddy Creek rises in the Laramie range, cutting 

 a remarkable canon through the eastern end of Casper Mountain, one of 

 upheaval and erosion combined. The eastern end of this singular ridge 

 is about fifteen miles southwest of the mouth of Muddy Creek, and con- 

 tinues nearly parallel with the Platte for twenty miles or more until it 

 ceases at the Eed Buttes. About noon of the 22d we left the Platte near 

 the mouth of the Muddy and struck across the intervening country in a 

 southeast direction, to make an examination of this interesting ridge. 

 The scenery at the head of the Muddy is very remarkable, and, so far as 

 dynamical geology is concerned, would well repay a week or two of dili- 

 gent study. Casper Ridge seems to trend nearly northeast and south- 

 west, and the rocks which cap the ridge dip slightly southeast. The 

 ridge is capped with carboniferous limestones and Potsdam sandstones, 

 and these form a high wall abutting northwest toward the Platte, as if 

 the whole mass had been lifted up eight hundred to one thousand feet 

 above the plains below, in a nearly horizontal position, and the edges had 

 been broken off all round, and the fragments are now found lying against 

 the sides in a highly inclined position, or have been washed away. The 

 eastern end has escaped erosion, for the ridges are here quite large. The 

 Muddy flows through a narrow valley, for a mile or two over a portion of the 

 red beds — a high ridge on the left, composed of heavy beds of bluish 

 limestone, red argillaceous sands and sandstones; immense beds, capped 

 with a massive bed of fine pudding stone, which I have usually regarded 

 as the bed of passage between the Jurassic and cretaceous. This is the 

 first time I have noticed these pudding-stone beds north of Cache a la 

 Poudre. They are well developed and persistent through Colorado and 

 New Mexico, but apparently disappear, in part or entirely north of the 

 Union Pacific Railroad. But here we find them appearing quite suddenly 

 in full development. Immense cubical masses have fallen from the 

 ridge, twenty feet thick. This pudding-stone is composed of smoothly 

 worn pebbles cemented in a paste of sand, and disintegrates slowly, and is 

 so hard that a fracture passes through the pebbles. It would polish well, 

 and make an excellent building rock. These tilted ridges seem to bend 

 around toward the south side of the Casper Ridge, and I have no doubt 

 it may be regarded as an oblong quaquaversal. The edges which have 

 broken off, or bent down, incline from all sides of the central portion. 



The Muddy Creek issues from Casper Ridge in two branches, cutting 

 deep and most picturesque gorges through the yellow and reddish car- 

 boniferous rocks. The walls of the canons show on the outside the 

 beds inclining 40° to 60°, but in the ridge the beds are nearly hori- 

 zontal from base to summit, five hundred to six hundred feet. These 

 gorges show quite clearly the anatomy of the ridges. Passing from the 

 east end of the ridge westward, we find that for about a mile the broken 



