VALLEY OF THE UPPER YAMPA RIVER. 183 



shales already seen, standing at a steep ang-le; they were also found near 

 the river, dipping gently to the westward. Although no fossils were 

 obtained which were sufficiently well preserved for specific determination, 

 little doubt was felt that these limestones belong to the Jurassic forma- 

 tion, and that the sandstones and shales overlying them represent respect- 

 ively the Dakota and Colorado groups of the Cretaceous. The shales 

 form a region of soft, rolling hills, included between Elk River and 

 Moore's Fork, where they are generally inclined at low angles, while 

 along the flanks of the Archaean rocks are occasional outcrops of steeply- 

 dipping sandstones, which have been referred to the Dakota Cretaceous. 



At the bend of Moore's Fork, the stream cuts through a ridge of white 

 and buff, coarse sandstones, which are reddened by local metamorphism and 

 oxidation of their ferruginous material. At this gap is a very interesting 

 group of springs, whose waters are charged with carbonic-acid gas and 

 sulphur. Unfortunately, we have no analysis of these waters, as the bottle, 

 in which some was carefully collected at the spring, was broken in transit 

 to the East. The presence of sulphur is, however, evident from the 

 color of the water and its peculiar odor, as well as from slight deposits of 

 sulphur around the edges of the springs, while the effervescence of the 

 carbonic acid is not to be mistaken. In the gravels on the eastern bank of 

 the river is one large pool, about 20 feet in diameter, of clear, bluish water, 

 out of the centre of which rises a little bubbling jet, several feet above the 

 surface, which would lead one to suppose at first glance that it was a boil- 

 ing spring. Several springs are found in the rocks to the west of the gap, 

 sometimes onl)^ a few inches in diameter, out of which the water issues in 

 a foaming jet, and in one instance having worn out a cave, of considerable 

 size, in the soft sandstone. The water is cold, and not unpleasant to 

 drink when freshly taken from the spring, though when warm the sulphur 

 gives it a disagreeable flatness. 



To the south of the gap is a broad Quaternary valley, whose surface is 

 covered with loose gravel and pebbles of the Archaean rocks. To the east of 

 this valley, the spurs of the Park Range rise up steeply, composed of coarse 

 gneisses and mica-schists, underlaid by granitoid rocks whose genei'al strike 

 is about north 15° east, with a dip of 50° to the westward. Just beyond 



