HOLMES.] GLACIAL PHENOMENA. 53 



When we come to searcli for the source of the granite, we are led to 

 observe an interesting fact. The only bodies of granite rock within the 

 limits of this valley are found either on the north side or on the bottom 

 at no considerable elevation above the river. But the erratic masses 

 occur to a great extent on the south side of the valley and at all eleva- 

 tions. In the vicinity of Mount Evarts they reach the upper surface of 

 the plateau more than 2,000 feet above the river bed. It- is evident 

 that these masses of granite were transported to their present resting 

 places either before the valley existed or that the ice streams were 

 so deep as to fill the valley to the brim and thus carry and strand 

 them. Still it is a question whether in the latter case these bowlders 

 would ever reach their positions on the south side — supposing the gla- 

 ciers to follow the course of the valley — as they would have to accom- 

 phsh the feat of crossing the whole width of the glacier as a boat would 

 cross a ferry. This could really only occur in case there should be such 

 an increase in the masses of ice descending from the highlands to the 

 north as to completely fill the valley, sweep across its course, and over- 

 spread th« broad table-land to the south. This table-land I have named 

 the Park Plateau; it is wholly volcanic, and is separated from the base 

 of the granite highlands on the north by the valley of the Yellowstone 

 proper, and by the East Fork, its geologic as well as topographic con- 

 tinuation. It extends, with but few interruptions, 100 miles to the 

 south. We are here led to inquire whether or not there are evidences 

 of former glaciers on this plateau. Such evidences do exist, but they 

 are certainly not such as we might expect. Instead of well-defined 

 moraines, an area dotted by erratic bowlders and broad expanses of 

 polished surfaces as in the Wind Eiver and Teton Mountains, we find 

 only a few rocks other than those that may have been derived from the 

 plateau itself. It should be remarked, however, in this connection, that 

 the soft rhyolites which form the greater part of the plateau would not 

 retain glacial markings for any considerable length of time. 



An occasional small block of granite indeed is found, and sometimes 

 at unexpected levels, as on the slopes of the Washburn Mount;ains, 

 many hundreds of feet above the general level of the plateau. A very 

 few have been observed beyond Mount Washburn, on the south side. 

 The most remarkable example of these is a bowlder resting upon the 

 brink of the grand caiion, about a mile and a half below the great falls 

 and nearly eighteen miles from the northern border of the plateau. 



On a stormy day in December I undertook to meander the Grand 

 Canon from the falls to the base of Mount Washburn, and during a 

 storm of rain and sleet took shelter under the overhanging edge of a 

 great rock in the dense timber. Considerably to my surprise I discov- 

 ered it to be a very compact, coarsely crystalline feldspathic granite. 

 In shape it is somewhat rectangular, the edges for the most part sharp 

 and unworn, the result of spawling by the heat of forest fires. In 

 cubical dimensions it will probably exceed 2,000 feet. It is within a 

 stone's throw of the brink of the canon and rests upon a sheet or a 

 series of sheets of rhyolite, not less than one thousand feet in thickness, 

 as may easily be determined by an examination of the section exposed 

 in the canon walls below. 



In seeking the possible source of this rock, we naturally turn to the 

 south, towards the sources of the Yellowstone. The plateau alone the 

 river's course and around the lake is totally volcanic. The great ranges 

 to the east and south of the lake are not known to contain a single ex- 



