GEOLOGICAL SURVEY OF THE TERRITORIES. 141 



ant. The character is so changeable that two sections taken ten miles 

 apart would not be identical, and in some cases not even very similar. 

 The more recent the age of formations the less persistent seem to be 

 their lithological characters over extended areas. 



From Black Buttes to Point of Bocks the dip is southeast. About 

 five miles west the principal bed of gray-brown sandstone rises to the 

 surface. The railroad runs through what I have termed a monoclinal 

 valley, that is, an interval between two upheaved ridges inclining in 

 the same direction, the high outcropping hills on the north side, and 

 the sloping portion on the other. The principal coal beds lie above the 

 massive bed of sandstone, which forms a line of separation between the 

 clays above, which are full of beds of coal, and the alternate beds of 

 sandstone and clay beneath, in which there are few seams of coal. 



The tendency of this sandstone to weather into curious forms and 

 cavities has given peculiar names to localities, as "Hermit's Grotto," 

 " Caves of the Sand," " Water- washed Caves of the Fairies," all of which 

 exhibit most singular, rounded cavities worn out of the sandstone, 

 sometimes extending into the bluff walls several feet. We may suppose 

 that most of these cavities originally contained a spherical concretion 

 which first determined their present rounded shape, and that the long- 

 continued action of the wind and storms has enlarged them to their 

 present dimensions. Perhaps, also, the trickling of water, or the process 

 of freezing and thawing, may have performed a part in disintegrating 

 the particles of sand. Here, too, we find preserved in the rocks the 

 greatest abundance of deciduous leaves of the poplar, ash, elm, maple, 

 &c, and among them some species which are found in the coal forma- 

 tions on the Upper Missouri. Among the fossil plants found is a spe- 

 cies of fan-palm, which, at the time it grew here, displayed a leaf of 

 enormous dimensions, sometimes having a spread of ten or twelve feet. 

 These gigantic palms seem to have formed a conspicuous feature among 

 the trees of these ancient forests. 



At almost every station, from Bitter Creek to Bock Springs, coal 

 mines are opened, and an abundant supply for railroad purposes can be 

 easily obtained. At one locality, near Point of Bocks, five beds were 

 opened in the same bluff, within a vertical height of eighty feet. These 

 beds are respectively five, one, four, three, and six and a half feet in 

 thickness. Near the summit of the hill, just over the coal, is a seam of 

 oyster shells six inches in thickness. The oyster is of an extinct and 

 undescribed species, about the size of our common edible one. 



There are also in this range of hills extensive beds of hard, tabular 

 layers of rock, which would make excellent flagging-stones. On the 

 surface are fine illustrations of wave and ripple markings, and at one 

 locality impressions which appear like the tracks of a mule on the soft 

 bottom ground. There are others that might be attributed to a huge 

 bird, and others to some four-toed pachyderm. Scattered all through 

 the coal strata are seams and concretionary masses of brown iron ore, 

 sometimes local and sometimes persistent over extended areas ; it occurs 

 mostly in a nodular form, and if the coal proves to possess sufficient 

 heating power to smelt it, the ore must become eventually of immense 

 economic value. There are also numerous chalybeate and sulphur 

 springs in the vicinity. 



About ten miles east of Salt Wells Station the high hills or bluffs on 

 either side disappear, and it is plain that we are passing across an anti- 

 clinal valley in which only the yielding clays of the upper cretaceous 

 period are seen. These clays have permitted the surface to be so 

 rounded off that a distinct anticlinal valley can be seen extending 



