GEOLOGICAL SURVEY OF THE TERRITORIES. 21 



ences which gradually wear out an anticlinal valley. These anticlinals 

 vary from a few hundred yards to many miles in length, involving a few 

 beds or all of them down to the granite. We regard each great: range of 

 mountains, as the Laramie range, Black Hills, Wind Eiver range, Big 

 Horn range, &c, anticlinals on a grand scale ; all the ridges, whether 

 composed of changed or unchanged rocks, inclining, step like, from one 

 central axis. 



In the distance, near the North Platte, a bluff-like wall can be seen, 

 composed of the White Eiver tertiary beds, nearly horizontal or inclin- 

 ing at a very small angle. This abrupt wall is more or less continuous 

 all along the shore of this ancient fresh-water lake, and marks steps in 

 the progress after erosion. It shows that the sediments once extended 

 up to the flanks of the mountains, with a thickness of several hundred 

 feet more than at present. Between this wall and the sides of the 

 mountains, which vary in distance from two to twenty miles, there 

 are always remnants more or less continuous, with greater or less thick- 

 ness. It is from underneath these beds that the older rocks appear, here 

 and there, over an area sometimes of cnly a few hundred feet, or extend- 

 ing several miles. About five miles lorth of La Bonte, close by the 

 traveled road, there is a somewhat rema kable conical butte, composed of 

 fine gray sandstones, portions of it approaching a quartzite. The butte 

 is about fifty feet high, with a dip 35° to the northeast, and looks like 

 a mass of rocks that had been transported from some other locality and 

 lodged there, for there are no others of the kind for a considerable dis- 

 tance on either side. The explanation appears to be, that this is an 

 isolated portion left after the erosion or denudation of this valley. About 

 half a mile to our left there is a long parallel ridge inclining northeast 

 toward the Platte, with the basset edges of the rocky layers on the 

 southwest side towards the road. At the base a small portion of the 

 red beds is visible ; above them the Jurassic series. Over the red beds, 

 and forming a sort of transition or bed of passage between them and 

 the Jurassic series above, is a layer of this same sandstone, thirty to 

 fifty feet in thickness. This anticlinal valley is about five miles in 

 length and a mile in width, and is now occupied almost entirely by the 

 red beds, while the gray sandstones, and doubtless the more recent 

 formations, Jurassic and cretaceous, extend over the whole area ; and 

 this butte, with a few masses of sandstone on some low elevations close 

 by it, is all that is left at the present time. I call them remnants, mon- 

 uments, or landmarks, left after erosion to assist us in reconstructing 

 the ancient form of the earth's surface. We cannot say that, because a 

 formation or series of formations do not exist over certain areas at the 

 present time, they did not once exist there, and that too in their fall 

 development. How these isolated portions escaped the general erosion 

 it is somewhat difficult to determine. The currents of water, which seem 

 to have come from the direction of the mountain range, were perhaps 

 turned aside by some obstruction thus passing around them ; no debris of 

 any kind has lodged on the sides of the butte. The entire plain country 

 of the West affords examples of these buttes, and I have often alluded 

 to them in former reports. Bijoux Hills, on the Missouri Eiver, Turtle 

 Hill, Deers Ears, Thunder Butte, Church Buttes, Pulpit Bock, and many 

 others which have been regarded as worthy of a place on our best 

 geographical maps, are examples of this kind. 



A glance at the map will show that the Laramie Mountains have bent 

 around westward so as to cause the upheaved ridges to incline about north- 

 east, and as the range continues to curve the ridges to incline north and 

 even to the northwest, following the bend of the axis of elevation. In the 



