84 



GEOLOGICAL SURVEY OF THE TERRITORIES. 



There is one feature in tlie 



geological 



Terraces. 



GNE133IC. 



Micaceous sandstones, 



Gray- 



limestone, with 

 trilobit&s. 



1 Brown limestone. 



SlLUBIAN. 



Bluelimeetone. 



structure of tlie mountains 

 of Montana, observed 

 by the survey of the 

 past seasons for the first 

 time and not noticed in 

 such a marked degree 

 in any other portion of 

 the West, and that is 

 the inversion of the sed- 

 imentary beds, so that 

 the oldest incline at a 

 greater or less angle on 

 those of more modern 

 ages. Thispheuomenon 

 occurs at a number of 

 places, but the most 

 marked are in the mid- 

 dle caijon of the Madi- 

 son, at the head of 

 Jackass Creek, and in 

 the East Gallatin range. 

 Several illustrations 

 are given in this report 

 which will render this 

 matter clear. The fol- 

 lowing illustration rep- 

 resents a section from 

 east to west through 

 the East Gallatin range. 

 (Fig. 24.) The Silurian 

 strata incline past a 

 vertical 30^ to 50^. The 

 central portions of the 

 range are Carbonifer- 

 ous limestones and are 

 nearly or quite vertical, 

 while eastward the Ju- 

 rassic, Cretaceous, and 

 ligiiitic strata incline 

 at various angles and 

 pass down in step-like 

 ridges to the valley of 

 ■Shield s's Elver, as they 

 were gradually elevated 

 by the ui)lift of the 

 range. We will not 

 enter into a discussion 

 here of the origin of 

 the forces that brought 

 about these results, but 

 it would appear that 

 there were two in ope- 

 ration, one which raised 

 the mass vertically, and 

 a side or tangential 

 force which crowded the Silurian beds over past a vertical. In some 



Whitish lime g t o n t-', 

 with spirifer, pru- 

 duclu.^, and i-t>r:il3. 



Cariwnifeuous. 



Gray limestones. 



Jurassic. 

 Limestone 

 ciuactzite. 



and 



Bed of Conglomerate, 



CUETACEOVS. 



Sandstones, with oa- 

 trca, Irigonia, iiio- 

 cenuiuis, etc. 



rEr.TIAKV. 



Soft Sandstunea, 



