' GEOLOGICAL SUEVEY OF THE TERRITORIES. 83 



Nowhere in Montana have I found the anticlinal folds or the synclinal 

 valleys so distinctly defined as in the interior basin of Utah. Still, 

 there are frequent local synclinals and anticlinals, as we find them 

 developed below the Three Forks. The prominent features, however, are 

 the widely-extended areas of elevation, though a single anticlinal may 

 embrace several apparently distinct raoges of mountains. Theoperatious 

 of the survey during the past season more strongly convince me of the 

 position that I have so often taken in my reports, of the originally wide- 

 extended and continuous cluiracter of the entire grouj) of sedimentary 

 strata ; that where that continuity is broken it is the result of upheaval 

 attended with erosion. It is possible that the later Tertiary group may 

 not have been continuous, but existed in basins. But from the Silurian 

 to the Upper Lignite group, inclusive, a thickness of 10,000 to 15,000 

 feet extended, °in an unbroken, horizontal mass, over nearly or quite the 

 entire area of Montana, and probably much more widely; and that 

 what Ave find remaining at the present time are only remnants of this 

 vast mass. Occasionally the entire series of formations is exposed,^ as 

 in the East Gallatin Eange, where for twenty miles, on a line from east 

 to west, the entire series of sedimentary strata may be seen from the 

 Silurian to the top of the Lignite group in consecutive order. (See Fig. 24.) 

 The groups of limestones and other rocks, as we see them inclining from 

 the Yellowstone Eange, in the Yellowstone Valley, show that they once ex- 

 tended uninterruptedly over the entire area, where now mountain-peaks 

 rise amid perpetual snows, 11,000 feet above the sea. The Silurian group 

 increases in importance as we proceed northward from the Three Forks, 

 and southward from that point it diminishes in thickness and changes 

 very much its mineral texture. Toward the south we find little of 

 the thin shaly and mud layers with the variegated sandstone, bat in 

 their stead, a quartzite passing up into a very hard, brittle limestone. 

 Still, we believe that this group in some form and with greater or less 

 thickness underlies the greater part of the Eocky Mountain region. 

 About the Black Hills of Dakota and the Big Horn Eange, the Potsdam 

 group presents a different mineral structure from the rocks of the same 

 age about the sources of the Missouri. 



The Carboniferous group, like most sea-deposited rocks, is very ^idely 

 distributed. It is probable that it will eventually appear that this 

 gToup of beds, as it is known, west of the Mississippi will be found to 

 cover a wider extent of territory and to maintain a more uniformly 

 similar mineral texture than any other formation in the scale. By 

 reference to the list of fossils prepared for this report by Mr. Meek, it 

 will be seen that, even in the most widely-separated localities, there 

 is a similarity or identity^ in the organic remains. Old Baldy, at the 

 head of Alder Gulch, forms a portion of a limestone-ridge in w})ich the 

 series of beds is shown vrith a vertical thickness of 1,000 to 2,000 

 feet and extends 'Off to the southwest, giving origin to the Stinking 

 Water, 'Black Tail Deer Creek, Eed Eock Creek, and many others. 

 These beds have a general dip to the southeast. We believe also that 

 the Jurassic and Cretaceous group had a very wide extension, though 

 perhaps not as great as that of the okler formations. They have been 

 more extensively w'orn away so that at the present time they occur in 

 fragments among the upheaved mountain-ridges and covering restricted 

 areas. So far as the position of the sedimentary rocks is concerned, 

 they may occur at any elevation. The beds may pass under the lowest 

 valleys or be found capping the gneissic rocks upon the summit of the 

 highest mountains. This is certainly not due to any inequality of the 

 surface of the gneissic rock prior to the deposition of the succeeding 

 beds, but unquestionably to upheaval. 



