viARviNE.] ■ GEOLOGY VALLEY OF THE BLUE RIVER. 185 



close to tbe stream. This first rise is perhaps about 100 feet to the top 

 of the lower terrace, then a long gentle rise to a subordinate terrace 

 (often absent) of 30 or 40 feet steep slop^, then another long slope to 

 the highest, but less distinct terrace, of 150 to 250 feet in height. Just 

 above the middle subordinate terrace another low terrace is sometimes 

 present. The lower slope is the most marked, and is often several 

 miles across. 



The Cretaceous shales are frequently exposed in the ravines and river- 

 channel. On the left is the hill of Station LXVIII, with the shorter 

 terraced slopes of coarse archaean debris. Mixed with this debris, on its 

 northwest side, is also much debris of shales, as if the Cretaceous rocks 

 laid up against the granite. In the ravines near the river some ex- 

 posures showed a bending of the strike of the strata from southward 

 around to the eastward, at first with a flat northward dip and then a 

 steeper southward one ; in other words, as if the strata were mantling 

 around the southern side of the archsean area of the Grand. Though 

 perhaps too few points were observed to make the fact absolutely cer- 

 tain, yet, where seen, the strata occupied just such positions as would 

 exist at the junction of two folds, one (perhaps the older) bringing the 

 granites of the Grand to the surface, with rocks here dipping off to the 

 south and west, the other, the Park-range fold, trending nearly at right 

 angles to the former, and lying just across its western end. Indeed, the 

 LXVIII hill, in its geological characters, is probably the complement 

 of the Lower Muddy Butte, and seems to be the southwestern extrem- 

 ity of the east and west fold of the Grand, which, judged by the un- 

 conformability at the Hot Springs, occurred before the deposition of 

 the lignitic beds, and preceding by a long interval the great final folding 

 of the mountains. 



About five miles from the Grand there rises above the terraced- slopes, 

 on the east, an escarpment of bedded rocks, about 400 feet high. These 

 are mostly of buff-colored with some brown friable sandstone, showing 

 in four prominent and nearly horizontal layers. At first, at the north- 

 ern end, a low dip to the south is apparent, again a probable indication 

 of the fold of the Grand. Their usual dip, however, is gently to the 

 east, and into the flattish-topped mass which they mostly make up, and 

 all along the west face of which they show in banded escarpments. The 

 exposures, meanwhile, in the ravines of the valley seem to be, so far as 

 observed, almost wholly of shales and slates, so that these bluffs would 

 appear to be the Upper Cretaceous sandstone No. 5. The horizon can be 

 quite readily traced by the eye all along the base of Williams Eiver Mount- 

 ains, and in it, near the south end of the range, was found an Inoceramus, 

 which Mr. Meek identifies as being closely allied to I. barabini, (Mor- 

 ton,) a fossil of Cretaceous No. 5, of the Nebraska section. All the lower 

 portions of the Williams Eiver Mountains, therefore, are composed of 

 Upper Cretaceous strata. 



For five or six miles these sandstones mostly form the flattish north- 

 ern arm of the range before it rises in rounded curves to its higher and 

 more ridge-like middle portions. At one point they are covered with a 

 large mass of apparently eruptive rock, probably basalt, or trachyte, 

 but which was not ascertained. Southwest of those lava-covered escarp- 

 ments are two dikes of trachy tic lava, which appear as low ridges cross- 

 ing the terraces on the east side of tbe valley, the westward trending 

 nearly south, the other trending more southwest; the two iutersectiug 

 near their southern ends. The one is vertical, the other apparently dip- 

 ping noithwest at an angle of 00^ toward the other, and probably joining 



