MAKVIKE.] 



GEOLOGY VALLEY OF THE MUDDY. 181 



timated. Following on eastward up the valley, all is covered with a 

 curious porous soil to its head, where the high escarpment of the great 

 volcanic mass is met. 



Flows of black basalt, lined with columned escarpments, great thick- 

 ness of volcanic conglomerate and white tuff, and red scoriaceous 

 masses show on this western face. The thickness of the volcanic mass 

 must exceed a thousand feet. The peculiar porous soil of the valley is 

 probably due to soft volcanic material. The ridge running toward the 

 exposure of the lower lignitic rocks (a) has some small lava masses on 

 it, while a long arm stretched northwestward would seem to indicate 

 the direction of the lava flow, which reached all around the northern 

 sources of the Muddy. 



Southward from the Upper Muddy Butte, the formation, as indicated 

 by the more frequently outcropping sandstone ridge of No. 5, would 

 seem to follow very closely, in its changing trends, the general course 

 of the river. The effect ou the topography of the intermingling of the 

 flat lake-beds with the including upturned Cretaceous, is here very curi- 

 ous. For ten miles down the river the lateral streams from the east are 

 very numerous, and have cut the lake-beds into long, often irregular, 

 tongues, whose ends fall in a steep terrace slope to the river, and the 

 sides falling similarly to the cutting ravines. These, however, often cut 

 through ridges of the Cretaceous sandstones at right angles to their 

 course, which close to a narrow cut the ravine-shaped valley, and mod- 

 ify in many ways the naturally regular forms of the lake-bed erosion. 

 The types of these tongues are flat and even, all of pretty uniform 

 length, with surfaces sweeping up in long, graceful curves to the gently 

 molded hills bordering the valley on the east, and which are probably 

 of the lignitic rocks. Near the river the Cretaceous shales, and the 

 sandstones just east of them, dip rather steeply or up to 30<^ or 40^ 

 eastward, but they flatten in going either east or west. West of the 

 upper part of this region, and partially encircled by the southward 

 bending of the Muddy, are the rolling hills of lake-beds, which have 

 been before referred to. South of these, however, the ridge in which 

 Station LXV is situated, is of a very different character. Northwest of 

 the station, and in the deep ravine at the base of the hill, is a small 

 ridge striking N. 40° E., and dipping 55° to the northwest. The beds 

 about show it to be swinging around the northern extremity of the sta- 

 tion, and beneath the hills of lake-beds just north. It is of limestone, 

 in all respects similar to the bed called No. 3, a few miles to the north- 

 west, and is undoubtedly the same bed. Following the main ridge 

 southward, this bed forms a minor, but parallel, ridge on its northwest 

 side, which dips as high as 65° in the same direction. The southern 

 end of the main ridge is quite broad and flat, and is surrounded by a 

 small palisade facing south and east, which appears to be the same bed 

 capping the hill and dipping gently east. It is through here that sec- 

 tion 3 (Plate III) is drawn. Outcrops of the same limestone, which is 

 still composed of two i^rominent layers, but is thicker than farther 

 north, appears as if broken downward along the east side of the ridge 

 also. All along the lower slopes upon this side the slates of No. 4, 

 where observed in the ravines in the confusing lake-beds, di])ped gently 

 eastward toward the river, some being barely inclined, and few, if any, 

 exceeding 30°. The ridge, indeed, is an anticlinal, with a gentle east 

 side, an abrupt west slope, trending about north-northeast, and flatten- 

 ing at the north. To have sections 3 and 2 (Plate III) in their i)roper 

 stratigraphical relations, section 3 should be moved eastward until the 

 anticlinal ou the lelt comes under the Upper Muddy Butte in section 2. 



