66 GEOLOGICAL SURVEY OF THE TERRITORIES, 



or aggregate of the sedimentary strata has been completely overturned. 

 A careful, detailed study of this interesting locality would show very 

 many instances of this overturning of the beds as well as faults of the 

 most remarkable character. Froin Bellevue Peak we started for the Snow 

 Mass range in a northwest direction. The dikes in the Cretaceous strata 

 were very numerous. The igneous matter seems to have been forced 

 up through fissures, in the rocks which were produced by the uplift. On 

 the west side of our trail the little stream which has worn out the deep 

 eaiion and forms the south branch of Eock Creek presents in the walls 

 a wonderful display of the beds inclining about southwest 5° to lO^. 

 The strata here indicate in a marked degree two primary movements, 

 the vertical and tangential. The summits of the ridges on the west side 

 of the high mountain-ridges, at least 13,000 feet above sea-level, are 

 capped with the black clays and quartzitic sandstones of the Cretaceous 

 group, while underneath are the variegated sandstones and quartzites, 

 more or less changed by heat. These rocks present every degree of 

 change to the most compact quartzites or slates. The whole must have 

 rested upon a viscous mass, and by strange manifestations of the force the 

 superincumbent strata have been tipped in every direction, and through 

 the fractures thus formed was squeezed, as it were, the melted granite, 

 forming the numerous dikes which occur everywhere and of every pos- 

 sible form and size. Sometimes an aggregate mass of several hundred 

 feet of well defined strata is bent in graceful curves. These examples 

 of flexure are very numerous, and vary from a slight bend to an arc of 

 a circle. The gorges which are cut deep down into the sides of these 

 ridges display the flexure as well as the faults and dikes in a remark- 

 ably clear manner. The variegated color of the beds adds greatly to 

 the picturesque beauty of the scenery. 



The Snow Mass range presents one of the most marked examples of 

 the complete subversion of the strata by the elevation of the great group 

 of granite peaks which form the core of that range. Our camp was 

 made in the valley of Eock Creek, on the south side of the range. The 

 high ridge which extends down from the southwest side is composed of 

 the double set of strata. The lower grouj), which holds nearly its normal 

 position, inclines at a small angle, while turned completely over on this 

 set or group is the same series in reverse order, like the overlaying of 

 sheets of paper or cloth. The Cretaceous shales are at least 60<^ past a 

 vertical, while the Jurassic, Triassic, and older beds incline at various 

 angles, varying from 60^ to 40^ past a vertical. The great group of 

 peaks which formed the center of the movement rises nearly 14,000 feet 

 above the level of the sea, and is composed of massive granite. The 

 jointing of this granite is very marked. One of the master-joints is 

 vertical with a direction about east and west. The joints are not all as 

 regular as the vertical, but they are so well defined that the mountain 

 is much broken up, and easily yields to the influence of air and moisture. 

 The sides and base of the range are covered with an immense quantity 

 of debris, the masses of rock varying in size from a few inches to 20 or 30 

 feet in diameter. In some instances the sides of the mountain seem 

 to be made of massive layers that break oft' in folio, as if the granite had 

 cooled in concentric layers. The entire range is in this way slowly but 

 constantly falling down, so that from base to summit the talus is quite 

 remarkable in quantity. At the base:Jon the south side, there is a 

 beautiful lake about 300 yards long and 150 wide, on which an abun- 

 dance of water-birds were swimming and feeding. This is named on the 

 map Elk Lake. The summit of the mountain is massive igneous granite, 

 remarkably compact. From the top of Snow Mass Peak the view is 



