HATDEN. 1 



GEOLOGY MORAINAL DEPOSITS. 55 



work, and, as the gorge increased in size, the power to excavate would be 

 increased. The crest of the range is covered with trachyte for miles, and 

 from that ridge extend down beautiful green vallej-s above timber-line. 

 The sides as well as the circular end of these gorges or valleys are cov- 

 ered with debris composed of the broken fragments of igneous or meta- 

 morphic rocks. All seem to originate in the same manner, and are con- 

 tinued by the same forces. The igneous rocks seem to have fliowed out 

 over the gneissic rocks to a considerable extent, at least 500 feet in 

 thickness, as is shown in this high mountain-valley, where the sides are 

 nearly vertical, and the bottom of the valley here and there reveals the 

 granitic rocks upon which the trachytes rest. So, we have in the main 

 range the same phenomena repeated that we find in all the southern 

 ranges, viz : a granitic nucleus or central mass, with dikes of igneous 

 rocks to a greater or less extent. The movements that elevated these 

 great ranges seem to have generated the heat that reduced the rocks in 

 certain portions of the crust to a fluid condition, and they came to the 

 surface in almost numberless places. 



We will not now discuss the history of the glacial period of the Eocky 

 Mountains, but simply state, in general terms, that the evidence seems 

 to point to a time when the Arkansas Valley was filled with one enor- 

 mous glacier, and that extending from it, on either side of the gulches, 

 were branches of greater or less magnitude ; that as the temperature 

 changed so that it was gradually reduced, and the physical conditions 

 approached those of the present time, the basins of the lakes were 

 scooped out, the morainal detritus was deposited, and finally the im- 

 mense granite bowlders were scattered over the surface. We shall 

 endeavor to show in a subsequent chapter that this glacial period was 

 one of great length, and that the gradual transition from the extreme 

 glacial cold to the present climatic conditions was of great duration, 

 and influenced the sculpturing of the surface to a very great extent. 



Our trail over the mountains led up the south branch of Lake Creek. 

 In many instances, these little branches have cut narrow channels into 

 the solid rock 30 feet in depth. This must have been done subsequently 

 to the melting away of the glaciers. 



About four miles up the valley the debris begins to be made up of 

 igneous rocks that have fallen down from the high ridges. There are, 

 also, immense masses of volcanic breccia, very compact, composed mostly 

 of granitic fragments of various sizes, some worn and others angular. 

 We see again the high crests capped with the igneous rocks, which 

 originally flowed from fissures in the granite, and, as the liquid rock 

 was ejected, fragments of the contiguous granitic rocks were worn off 

 and inclosed. This fork also branches off to the north toward Eed 

 Eock Pass, and the usual signs of the wearing out of these vast mount- 

 ain amphitheaters can be seen. The valley, or gorge, here is unusu- 

 ally broad, and yet the abrupt walls on either side show its origin. 

 The ridges are all capped with the igneous rocks, and, in some instances, 

 they are a brilliant red. The gorge is cut deep down into the granitic 

 rock, and, when it is not concealed by detrital matter in the bottom of 

 the valley, is worn smooth. 



We ascend the steep sides of the divide between the waters of the 

 Pacific and those of the Atlantic, by way of Lake Creek Pass. The 

 melting of the snow keeps the sides of the mountain, where covered 

 with loose earth, in a boggy condition, which impedes traveling. U))oii 

 the summit of the pass is a little lake or reservoir for the water from 

 the melting snows. On both sides are high walls about a fourth of a 

 mile apart, between which is located tbe pass. It is not so very nuicL 



