GEOLOGICAL SUEVEY OF THE TERRITORIES. 43 



25°, while the limestones form the entire upper portion of a peak which 

 rises to a height of over 1 0,000 feet above tide-water. It is probable 

 that a portion of this Coal group is of Cretaceous age, but I also believe 

 that the beds pass up into the Tertiary period, as we find them in other 

 IDortions of the West. Ammonites and baculites and other Cretaceous 

 shells were found below the coal in a fine state of preservation, but no 

 plants or other fossils were found above. On the east side of the Yel- 

 lowstone the more modern beds, probably Tertiary, are largely shown, 

 inclining in such a way as to indicate that the Yellowstone had made 

 its way, for a few miles here, through an anticlinal fissure. Opposite 

 the Hot Springs on Gardiner's Eiver, there is a vertical wall of Creta- 

 ceous and Tertiary strata, exposing 1,500 feet or more in thickness. Coal- 

 beds occur here also. All the way to Tower Falls, or the foot of the 

 Grand Cafion, fragments of the sedimentary group occur of greater or less 

 extent. They crop out from ainder mountains of volcanic conglomerate 

 and basalt. The evidence becomes stronger every year of exploration 

 that the erosive forces have acted on a more stupendous scale than I 

 have ever conceived or expressed in any of my former reports ; that the 

 entire series of sedimentary strata, from the lowest Silurian to the high- 

 est Tertiary known in the West, has extended in an unbroken mass all 

 over the Northwest ; and we find here and there by the exposure of the 

 entire series, as at Cinnabar Mountain, and in many other localities, the 

 most satisfactory proof of the statement which I have so often made. 

 This single statement implies that from 10,000 to 15,000 feet in thickness 

 of unchanged rocks have been removed from this mountain-region, except 

 what might be called remnants left behind, occupying restricted areas. 

 Of course, the older the group the larger the area over which it has es- 

 caped erosion. The hard and compact limestones of the Carboniferous 

 and Silurian ages are found to a greater or less extent all over the North- 

 west. They yield much less readily than the more modern beds, and 

 are consequently found on the summits of some of the highest mountains, 

 10,000 and 12,000 feet above the sea. Indeed, these isolated patches of 

 all the formations which occur here and there render it necessary to ex- 

 plore the country, with much detail, in order to prepare a geological map 

 in colors with any degree of accuracy. These isolated fragments are 

 liable to be met with in the most unexpected places — on the tops of 

 mountains, or cropping out of the sides of caiions or ravines. Around 

 the sources of Gardiner's Eiver and Tower Creek, the mountains and 

 hills appear to be entirely of volcanic origin at a distance, and many 

 of them are ,• but underneath the vast volcanic mass, is a series of the 

 grayish-brown beds of the Coal group, so that many of the lower hills 

 from which the volcanic material has been denuded are covered with an 

 indurated calcareous clay, filled with deciduous leaves in an excellent 

 state of preservation. Farther down these streams, toward their junc- 

 tion with the Yellowstone, outcroppingsof the true Cretaceous, Jurassic, 

 and Carboniferous occur here and there. To what extent these trachytes 

 and volcanic conglomerates covered the surface at one time, it is hardly 

 possible to determine, but there is evidence that they must have ex- 

 tended in an unbroken mass over a very large area. 



The question continually arises in the mind. At what time in geologi- 

 cal history did this period of intense volcanic activity occur'? Evidences 

 of greater or less igneous action are found in rocks of all ages, from the 

 lowest metamorphic u]) to the present time, but there seems to have 

 been, as it were, a culmination of the volcanic forces some time during the 

 later Tertiary period. It may be that the accumulated forces, which had 

 been since the Cretaceous era gathering in the interior of the earth, 



