196 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. 



Grouse Creek on the broad 90-foot lacustrine bench of the older and larger 

 Yellowstone Lake. 



On the west side of the moraine across which runs the continental 

 divide there is an abrupt descent to a characteristic glacial lake. From 

 this lake flows Outlet Creek, the sluggish stream before mentioned. Across 

 the west end of Outlet Canyon there stretches a somewhat formidable 

 barrier in the shape of a moraine. Upon reaching this barrier the stream 

 deviates to the northwest and cuts its narrow channel through the gravel 

 under the north wall of the canyon. Descending rapidly through the 

 accumulated drift, it comes out once more upon the old river channel, and 

 soon pours its waters into Heart River and out through the Snake to the 

 Columbia, 



CHANNEL MOUNTAIN. 



Outlet Canyon north of Chicken Ridge presents many of the same 

 physical features as those noted to the southward, and offers no special 

 points of geological interest. A conical hill which forms the southern spur 

 of Channel Mountain affords an excellent bird's-eye view of Outlet Canyon, 

 its mural face rising high above the river channel. 



From this hill the Montana formation can be traced northward along 

 the summit of Channel Mountain, a conspicuous and timbered point 9,000 

 feet above sea level. The sandstones of Channel Mountain do not differ 

 essentially from those of Mount Hancock and Barlow Peak. From this 

 culminating peak Chicken Ridge gradually falls away toward the lake on 

 the north and east. 



Lacustrine deposits skirt the lake shore, attaining an elevation of nearly 

 8,000 feet above sea level. Still above this in certain localities come the 

 remnants of glacial drift, resting indiscriminately upon rhyolite and Creta- 

 ceous sandstones. Rhyolite encircles the ridge on all sides, while the cen- 

 tral body consists of the. ever-persistent Montana sandstone. 



FLAT MOUNTAIN. 



It may be well to call attention to the fact that near the lake shore, 

 at the northwest base of Flat Mountain, there comes to the surface from 

 beneath the rhyolite an outcrop of sedimentary rocks, exposed by the erosion 

 of the lava along the southern prolongation of Flat Mountain arm. A short 



