156 ^ PROCEEDINGS OF THE ACADEMY OP 



Lands. They remind one of some ancient city with its palaces, domes and 

 towers. At the mouth of Mule Creek we have one of the most picturesque views 

 in this region. An area of two miles wide and six miles long has been worn 

 away by the eroding agency of water into myriads of conical and pyramidal 

 peaks, high sharp ridges and deep winding canons two hundred and fifty 

 to three hundred feet in depth. The summits of these ridges are capped with 

 layers of coarse-grained sandstone, containing many whitish particles of clay 

 which have been dissolved out by exposure, and give to the rock the appearance 

 of worm-eaten masses. We then have underneath the sandstone a yellowish 

 calcareous marl passing down into a light gray grit ; then the flesh-colored 

 Turtle bed with its peculiar fossils. Most of the same organic remains are found 

 here as at Bear Creek or Ash Grove Spring, but not near so abundant. A 

 species of land shell, Helix Leidyi, a single specimen of which was discovered 

 at Bear Creek in 1853 by Mr. Meek and the writer, occurs at this locality in 

 great numbers. Continuing our course down the south bank of White River, 

 we see on our left the main range of the Bad Lands rising high above the sur- 

 rounding country, and extending in an easterly direction to the head of Teton 

 River, where it ceases abruptly. On our left as far as the eye can reach we see 

 outliers of the Tertiary exposing their whitened surfaces, and resting upon Cre- 

 taceous bed No. 5. 



Nearly in a direct line south of Grindstone Hills, and near the dividing ridge 

 between White and Running Water Rivers, we meet with a high outlier of 

 Tertiary called Eagle Nest Hill, from the fact that an eagle has built her nest 

 on its summit from time immemorial. This hill is about eighty feet in height 

 above the surrounding prairie, with nearly perpendicular sides, composed 

 mostly of indurated clay with a mixture of calcareous matter. Not far distant 

 is another hill of the same formation, about a mile long, and covered to some 

 extent with pines and capped with a bed of sandstone twenty to thirty feet in 

 thickness. All around the base of these hills the Cretaceous bed No. 5 is 

 seen with a few of its peculiar fossils. 



About ten miles north east of this point, near White River, we meet with a 

 denuded area which presents some peculiarities worthy of note. Here I ob- 

 served a vertical seam of fine-grained sandstone passing through the different 

 strata for several hundred yards, varying in thickness from four to thirty inches. 

 Sometimes this vertical seam is left standing, the more yielding calcareous 

 marl having been washed away from either side, and thus it forms a high 

 jierpendicular wall having much the appearance of mason work. It is com- 

 posed of a fine, light gray grit, and is doubtless due to the infiltration of fine 

 sediment in a fissure in the strata. At this locality we have, in descending 

 order, rather fine grained gray sandstone, then a yellowish or flesh-colored 

 calcareous marl, containing many tough argillo-calcareous concretions. This 

 forms bed E of vertical section, and contains at this locality numerous remains 

 of turtles and mammals. Within the space of a mile I saw of turtles — portions 

 more or less entire — more than thirty individuals. Fragments also of Oreodon, 

 Rhinoceros and several new species of Mammalia, one of which Dr. Leidy has 

 described as Steneofiber Nebrascensis, 



We continue to see quite numerous isolated patches of this deposit until 

 reaching the forks of White River, below which point they almost entirely 

 cease, and the river cuts deeply through Cretaceous bed No. 5 into No. 4. 

 The alluvial bottoms are composed of the light-colored clays and sands 

 of the Bad Lands, but the bluffs are formed of the yellow and dark ash- 

 (•olored clays of the Cretaceous formation, with a few fossils, as BactiUtes, 

 Ammonites, Inoceramus, S^c. Passing down the Slissouri River, the next indica- 

 tion of the Tertiary deposit is at Medicine Hills, about eighty miles below Fort 

 Pierre. These are a lofty group of hills, the upper portions and sides of which 

 are covered with large fragments of rocks, which seem to have been removed 

 from their position by denudation. This rock holds the same geological 

 position and is similar to that on Bijou Hills, but is, in some instances, of a 



[June, 



