262 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



The same strata were observed by me, in 1856, further south on Rock Creek, a 

 branch of the Republican River, near longitude 102°, where I found similar seeds, and 

 at some points northeast from there, on the upland, toward South Platte River. I then 

 was inclined to consider them as Post-Tertiary. A similar formation, lower down on 

 the Republican River, below the mouth of Frenchman's Fork, and thence to near lon- 

 gitude 97° 20', may be of the same age, or perhaps a little older. The strata on 

 Lodge Pole Creek, near the Pine Bluffs, present a similar character, and are probably 

 of the same age, or only little older. They are, partly at least, more regularly strati- 

 fied, and some of them are conglomeratic, or coarse-grit stones ; but such differences 

 may be occasioned by the geographical distance of the two points. There I also 

 found the seeds of Celtis. The more conglomeratic portion may, however, correspond 

 to No. E of Dr. Hayden's section. 



FROM ASH HOLLOW TO BEYOND SCOTT'S BLUFFS. 



From Ash Hollow westward, the strata gradually assume a different appearance, 

 and instead of being calcareo-arenaceous they become more purely arenaceous, and 

 finally argillo-arenaceous. The main body of the formation is made up of the very 

 finest, light-brown, or buff-colored sand, with a slight admixture only of clay, just 

 enough to make it hold together, and stand in vertical exposures. Only the lower 

 strata are a little more clayey. But there are interstratilicafions of coarser sand and 

 sandstones, in which the cement, however, is not carbonate of lime, and which mostly 

 form no regular continuous beds. These strata present numerous precipices and high 

 cliffs, with vertical bare walls and turreted appearance, some of which have attracted 

 the attention of every traveler, and are known as prominent landmarks. On account 

 of the variability of their character it is more difficult to trace their superposition than 

 it would appear on a superficial examination ; and the dip does not seem to be quite 

 uniform throughout, but it is generally a few degrees to the east. All my observations 

 combined, leave, however, no doubt that this formation is older than the Ash Hollow 

 series ; and the remains of animals in the lowest portion of these strata, near Scott's 

 Bluffs, seem to indicate that it is of the age of the White River formation, viz, Mio- 

 cene-Tertiary. The total thickness of this series is probablv not much less than 1,000 

 feet, or even more. 



At the mouth of Ash Hollow the lowest 30 feet are occupied by a stratum of 

 buff-colored, finely arenaceous material, with no visible cement, but rather compact, 

 capped by the calcareous sandstones. Up the river the arenaceous bed, or beds, rise 

 more and more, and exhibit occasionally harder portions of the same color, like irreg- 

 ular rocky interstratirications, although these are not very prominent. Within 14 miles 

 they attain an altitude of nearly 200 feet, indicating a rise of about 12 feet per mile 

 more than the fall of the river. In a prominent bluff there the stratification is indi- 

 cated by steps or terraces in the bare escarpment, on which the sand is mostly a little 

 coarser and better cemented, but more in concretions and irregular seams than in dis- 

 tinct layers, and without changing much the uniform appearance of the face. The 

 upper 10 feet are compact sandstone, and the bluff is capped by some strata of the cal- 

 careous drift-stone. Near by, a few ledges of a calcareous sandstone, with softer 

 interstratifications, were also noticed near the water-level. 



