24 GEOLOGICAL SURVEY OF THE TERRITORIES. 



I 



from whif'li those streams take their rise. As we descend the Madison 

 we tind that the vaHey seems to pass alonj? a sort of anticlinal axis, and 

 an each side lofty, nearly vertical walls of trachyte, arranged in thick 

 layers. The lower portion ai)pears to yield qnite readily to atmospheric 

 agencies, owing' to the ferruginous matter contained, which renders it a 

 loosely aggregated mass of crystals of feldspar. As wa ascend ui)ward 

 the rocks become more compact, and the upper layers are a cellular tra- 

 chyte. In some places the up[)er compact beds assume a columnar 

 structure, breaking into the form of verti(;al columns; these break in 

 l)ieces and cover the sides of the hills with masses of rock. Lower 

 down on the Madison we find layers of the red feldspar, whicli ]>resent 

 the api)earance of stratified beds like the Azoic rocks, with an inclina- 

 tion in the same direction with the overlying basaltic rocks. There are 

 numerous seams of white quartz, also trap, running across the country 

 in every direction, many of which indicate the presence of gold-bearing 

 rock. The summits, or crests, of the high mountains are ragged, not 

 from erosions since upheaval, but owing to the manner of the upheaval. 

 Each peak assumes, to a certain extent, the form of an independent uplift, 

 with layers of rock inclining around from every side; and yet it is by a 

 series of these peaks connected together, more or less, that a mountain 

 range is formed. Wherever tliese peaks or groups of peaks are sei)arated 

 a short distance, a low point is made in the range, which gives passage to 

 streams. A^'iy many of theselow passeshaveno streams issuingfrom them 

 at this time. The Madison forms a canon by cutting tbrough one of these 

 lofty ridges at the upper portion of the Burnt Hole, and a second one at 

 the lower end of the same valley. Still below the feldspar beds and 

 near the junction of the Three Forks of the Missouri we have beds of 

 exceedingly slaty chaiacter, inclining at angles of 31° and passing down 

 into the granitoid rocks below. 



" In the valleys of these streams is a series of marls and marly sands 

 and conglomerates, precisely like the upper beds of the AVhite liiver 

 Tertiary. These marls are mostly of a tiesh-color, sometimes assuming 

 the texture of a quartzose sandstone. Its greatest thickness in this 

 region is about 200 feet, and not conforming to the Carboniferous rocks 

 beneath, but inclining in the same direction about 8°. 



" The Carboniferous rocks are largely developed in this region, and 

 incline at very large angles Irom the mountains. The lower part of 

 these limestones have been so atfected by heat that the stratification has 

 been very nearly obliterated, and presents a very rough api>earance. 

 Above this is a bed which is undoubtedly Carboniferous limestone 

 changed, but which now very much resembles basalt, but contains more 

 arenaceous matter, and appears to have had the stratification but partially 

 changed. From the Three Forks these limestones extend westward or 

 southwestward about twenty to twenty-five miles, and then continued 

 northward toward the gate of the mountains along the Missouri. They 

 also extend to the northwest to a range of mountains, in which is the 

 Blackfowt Pass of Lewis and Clarke. 



" r////// 3. — Visited the plateau, mentioned by Lewis and Clarke, be- 

 tween the mouths of the Gallatin and ^ladison. It is a long flat ridge 

 of limestone, representing the portion of the inclined rocks which form 

 the left side of the canon below. 



" The rocks on that side incline 2-1", (x^ntinuing far on the distant hills. 

 The base of this small ridge is a bluish cherty limestone, sometimes yel- 

 lowish, very compact or hard, breaking into fragments just like the 

 Carl)onit('r()us limestones before seen. J)i[). 33". This bed corresponds 

 with a portion ol the right side of the canon next to the water. There arc 



