140 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



west and southwest, at a variety of angles, 15^ to 80°. East of tMs 

 ridge the Eocene and Cretaceous formations prevail. 



As we descend the Gallatin, below Flathead Pass, a series of dark- 

 brown quartzites, sandstones, and pudding-stones rise up from beneath 

 the limestones. Some of the sandstones are very micaceous, as if they 

 had been formed out of mica slates of the metamorphic series. I esti- 

 mated the thickness to be 1,000 feet, and I have not observed it anywhere 

 else along the sources of the Missouri. Ko fossils were observed, and the 

 rocks themselves did not seem to promise any. They may possibly be 

 remnants of the Lower Silurian series, left from erosion prior to the de- 

 position of the Carboniferous ; at any rate, they appear very old, even 

 partially metamorphosed. The dip of these beds is variable, 10^ to 25^ 

 northwest, though some local inclinations are greater, with a trend north- 

 east and southwest. These rocks extend across the Gallatin, and under- 

 lie, to some extent, the terraces and Pliocene deposits between the forks. 

 The Gallatin River passes across the edges of this series, showing the 

 uplifted strata on both sides, passing up into massive limestones and 

 reddish sandstones. The lower series exhibits all the usual signs of 

 mud flats and shallow- water deposits in quite a remarkable degree. It 

 may be that the center groui)S, from the metamophic strata up, are of 

 Carboniferous age. 



Is ear the junction of the Three Forks, the Pliocene beds are well 

 shown, and on both sides of the Madison, for ten miles or more above 

 the junction. The bluffs on either side are high, composed of the light- 

 colored clays, sands, and sandstones of the lake deposits. A careful 

 examination, I have no doubt, would have shown the existence of ver- 

 tebrate remains. I heard of the discovery of bones, teeth, and turtles by 

 the farmers, but could not secure any. 



The Missouri below the Three Forks, passes through a canon formed of 

 the clays and massive limestones of Carboniferous age. On the south 

 and west side of the Jeftersou the dip, which is slight, 5^ to 10^, appears 

 to be about northwest. About six miles above the junction the lime- 

 stones rise up from beneath the lake deposits on the south side of the 

 Jeflerson in the ridge which forms the tongue or wedge between the 

 Jefferson and Madison. The dip is north and northwest, 45°. Imme- 

 diately underneath the limestones are the usual gneissic strata, that con- 

 tain the gold ores. It is not common for any other beds to be brought 

 to the surface between the well-known Carboniferous and the metamor- 

 phic ; and so far as the sources of the Missouri and the Eocky Mount- 

 ain divide, it is not uncommon for large areas to be occupied by no beds 

 newer than the Carboniferous. 



In the valleys of the Gallatin, Madison, and Jefferson, we find, on the 

 east side of the Gallatin, a range of Carboniferous limestone mountains 

 rising up 8,000 to 9,500 feet above the level of the sea. On the north and 

 west side of the Jefferson, these limestones form high, nearly vertical walls, 

 but between these walls the lake deposits extend up the valleys and form 

 the tongues or ridges that extend down between, for ten miles or more, 

 and it is only here and there that the older rocks crop out. The lake 

 deposits fill the valleys and lap on to the sides of the hills ou either side. 

 The caiion of the Missouri, below the junction of the Three Forks, was 

 evidently the outlet of the lake, that had its deepest portion around the 

 Three Forks, and set high up in the valleys to the mountains at their 

 sources. Ascending the valley of the Jeflerson, we passed over the 

 high hills on the east side, to avoid the deep caiion through which the 

 river ran for several miles. Granitic strata cropped out in the valleys 

 or gorges, with now and then a protrusion of trachytic basalt. The 



