68 GEOLOGICAL SUKVEY OF THE TERRITORIES. 



year slowly moved downward, carrying with it great quantities of earth 

 and fragments of rock far below. The time for this action in its full 

 force is now past, and the work of excavation could not have been per- 

 formed, as we see it has been done in past ages, with the forces now in 

 operation. 



Between the two main peaks, each of which is nearly 14,000 feet high, 

 the crest curves so as to form a full semicircle, and has been worn away 

 so that it is now 500 to 800 feet lower than these peaks, though it must 

 have bee^ originally of the same height at least. We may see that it is 

 most probable that much of the original form of these mountain-ranges has 

 been lost, and that their present shape is the result of atmospheric 

 forces acting through ages — from the time of the uplift to the present day. 

 It is also evident that these eroding agencies operated with far more 

 power in the past than at present, and that it is most probable this force 

 has been decreasing slowly to the present time. The Blue River range 

 is a fine illustration of the same process of excavation. The Snow Mass 

 Peak is really a long, sharp ridge with two points, the northwest point 

 'being about 300 feet higher than the southeast one, while between the two 

 the crest has been worn away so that it is 600 to 800 feet lower than the 

 two ends. The shape seems to be given by the flexures of the 

 jointing. The sides are deeply furrowed, down which it is probable 

 that masses of snow and ice have slidden for ages. On the south 

 side these furrows are very deep and regular, and at about the same 

 distance apart, so that the curved form appears like a series of waves, 

 extending from the summit down into the amphitheater. There can be 

 no doubt but that they have been worn down by the combined action 

 of water and ice. The square masses of granite stand up on these crests 

 or ridges like druidical columns. The remarkably broken condition of 

 the rocks composing the entire nucleus of these mountains would indicate 

 immense wear, and that all these peaks which are now very lofty were 

 once much higher than at the present time. On the south side of Snow 

 Mass, near its base, there are vast masses of igneous rocks that appear 

 to be of more modern age. Much of the basalt being porous like 

 slag. It is most probable that the igneous rocks are of different ages, 

 and while none of them in their i)resent form may be older than the 

 Cretaceous period, there may have been eruptions of greater or less ex- 

 tent all the way up to the present period. In tracing the channel of 

 Eock Creek up from our camp, we find the black Cretaceous clays dip- 

 ping past a vertical 50° to 60°. The channel of the little stream reveals 

 a complete section of the beds in their order, as well as their position. 

 We find two distinct sets of beds, the upper reversed, so that at the 

 upper falls we find the quartzites of the Dakota group on the black 

 clays of No. 2, and the latter over tlie limestones that usually charac- 

 terize No. 3. Near the lower part I obtained quite a collection of well- 

 marked Cretaceous fossils, among them Baculites, Tnoceramus, and many 

 small shells. In the gray limestone are numbers of a high, round Inoce- 

 ramus identical with the species found on the east slope of the Rocky 

 Mountains. In No. 2 I found Ammonites, Ostrea congesta, and a small 

 shell with scalloped edges like O. larva. These shales and clays are more 

 or less metamorphosed at different localities. 



In the little streams that flow from the high mountains are nu- 

 merous beautiful cascades. There is in most instances a reason 

 why the water should be interrupted ; and there are two excellent 

 examples in this stream above our camp toward its sources. The 

 upper falls are produced by the water flowing over the hard 



