GEOLOGICAL SURVEY OF THE TEERITOEIES. 81 



admit of the same e'splanatioii. Both undoubtedly form safety-valves 

 or vents for the escape of the powerful forces that have been gener- 

 ated in the interior of the earth since the commencement of our pres- 

 ent period; the true volcanic action has ceased, but the safety-valves 

 are the thousands of hot springs all over this great are^. I believe 

 that the time of the greatest volcanic activity occurred during the 

 Pliocene period — smoke, ashes, fragments of rock, and lava i)oured 

 forth from thousands of orifices into the surrounding waters. Hundreds 

 of cones were built up, fragments of which still remain 5 and around them 

 were arranged by the water the dust and fragments of rock, the ejectamenta 

 of these volcanoes, in the form of the conglomerate or breccia as we find 

 it now. These orifices may have been of every possible form — rounded 

 or oblong, mere fissures, perhaps, extending for miles, and building uj) 

 their own crater rims as the hot springs build up their rounded, conical 

 peaks or oblong mounds at the present time. It is not necessary to 

 enter into the history and origin of either hot springs or volcanoes in 

 this connection. The causes which have produced the phenomena here, 

 either in the Pliocene period or the present, are the same all over the 

 world, and have been favorite topics of discussion by men of science. 



CHAPTER v.* 

 THE GRAND CAHON— FALLS— HOT SPRINGS— YELLOWSTONE LAKE. 



We will now enter upon a description of the Yellowstone Basin proper, 

 in which the greater portion of the interesting scenery and wonders is 

 located. The term is sometimes applied to the entire valley, but the 

 basin proper comprises only that j)ortion inclosed within the remarkable 

 ranges of mountains which give origin to the waters of the Yellowstone 

 south of Mount Washburn and the G'rand Canon. The range of which 

 Mount Washburn is a conspicuous peak seems to form the north wall 

 or rim, extending nearly east and west across the Yellowstone, and it 

 is through this portion of the rim that the river has cut its channel, 

 forming the remarkable falls and the still more wonderful canon. The 

 area of this basin is about fort\ miles in length. From the summit of 

 Mount Washburn, a bird's-eye view of the entire basin may be obtained, 

 with the mountains surrounding it on every side without any apparent 

 break in the rim. This basin has been called by some travelers the 

 vast crater of an ancient volcano. It is probable that during the Plio- 

 cene period the entire country drained by the sources of the Yellow- 

 stone and the Columbia was the scene of as great volcanic activity as 

 that of any portion of the globe. It might be called one vast crater, 

 made uj) of thousands of smaller volcanic vents and fissures, out of 

 which the fluid interior of the earth, fragments of rock, and volcanic 

 dust were poured in unlimited quantities. Hundreds of the nuclei or 

 cores of these volcanic vents are now remaining, some of them rising to 

 a height of 10,000 to 11,000 feet above the sea. Mounts Doane, Lang- 

 ford, Stevenson, and more tlian a hundred other peaks may be seen 

 from any high point on either side of the basin, each of which formed a 

 center of effusion. Indeed, the hot springs and geysers of this region, 

 at the present time, are nothing more than the closing stages of that 

 wonderful period of volcanic action that began in Tertiary times. In 

 other words, they are the escape-pipes or vents for those internal forces 

 whiclj once were so active, but are now continually dying out. 



* An, abstract of Chapters V and VI was published in the February and March aum- 

 bera oi the American Journal of Science. 



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