HOLMES.] THE GRAND CANON. 37 



plateau. K it could be ascertaiued that they really are lake beds they 

 would take a very important place in our discussions of the erosion of 

 this caQon and the drainage of the old lake, but it seems to me that 

 they may be simply beds of alluvial material formed by the river before 

 the falls had receded to their present position. At the falls, however, 

 we are really within the borders of the ancient Yellowstone Lake, and 

 the lake beds play an important part in the geology of the locality. 

 The wall of the cafion between the Upper and Lower Falls, on the east 

 side, is capped with about 20 feet of horizontally-bedded sandstones, 

 under which are 30 feet of sandy clays. These are at a height of about 

 100 feet above the top of the Upper Falls. In the banks of the river, 

 near the head of the rapids, similar strata outcrop at a height of from 

 101) to 150 feet above the river. The low, grassy hills that lie along the 

 east side of the river, and the sage-covered terraces bordering the 

 broad valley of Sour Creek, are probably composed chiefly of the lake 

 beds. They occur also on the west side of the river both above and 

 below the falls, and have their greatest development in Hayden's Valley, 

 about 10 miles above. They rest upon the uneven surface of the pitch- 

 stones, rhyolites, and mixed, igneous rocks that constitute the body of 

 the great plateau. In Plate XXXI, I give an approximate outline of 

 the ancient lake in which these formations were deposited. 



On the morning of the 5th I left the falls with the intention of pass- 

 ing down the western side of the caiion and between the canon and 

 Mount Washburn. At the request of Mr. Gannett I undertook to make a 

 meander of the river course. The work proved to be very tedious, as it 

 was quite impossible to know the approaches to the salient angles of 

 the canon wall on account of the dense timber, and much time was re- 

 quired to follow the sinuosities of the brink. Looking down from the 

 cliff west of the falls,- the view is cut off by a great white promontory, 

 the steep, outer x)oint of which projects forward and overhangs the 

 river. This promontory is probably nearly a mile below the falls. The 

 walls of the caQon, from the falls to this point and a short distance be- 

 yond, are extraordinary in form and color. They have already been de- 

 scribed by many visitors. The rocks are all rhyolites (Ko. 9, of Cai)tain 

 Button's catalogue), mostly of whitish and grayish colors, which have 

 been stained by the oxidization of minerals. As a rule the walls do 

 not present broad, vertical faces, the jjeculiar jointage of the rocks hav- 

 ing a tendency to produce steep buttressed slopes. Below the white 

 promontor,y the character of the walls is greatly changed. The rocks 

 are brownish and grayish rhyolites, which weather very dark, and are 

 so amorphous and compact as to form walls remarkably steep and per- 

 sistent. On the eastern side, beginning opposite promontory point and 

 extending down nearly two miles, we have the finest wall exhibited any- 

 where in the caiion. The canon is here about 1,000 feet deep, the upper half 

 of the wall being a sheer i)recipice. The dark-brownish face is scarred 

 and seamed in a most remarkable manner. There is apparently a tend- 

 ency to the columnar structure. The joints have the greatest diversity 

 of directions, extending in great sweeping curves across the wall, reach- 

 ing from base to summit in almost straight lines or arranged in groups 

 set at all angles with each other. Down the middle portion of this 

 scarred wall a cascade falls. In the upper 500 feet the thread of water 

 slides down the almost vertical groove which it has cut for itself. Below 

 it strikes the debris talus and sinks from sight. The debris slope is for 

 the most part covered with trees. An attempt to sketch this fine wall 

 was defeated by a rain-storm, which, unfortunately, continued most of 

 the day. At the lower end of the wall, and nearly three miles below the 



