208 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



River the gneiss is overlain by a remnant of the limestones that once cov- 

 ered it. The rock sequence of Cambrian and higher rocks has not been 

 recognized, and it is probable that a fault exists between the exposures of 

 the gneiss and of the limestone, for the latter carries poorly preserved fossils 

 of Carboniferous types, the beds dipping gently to the southeast at 5° and 

 forming low rounded knolls near the wagon road. These limestones are 

 somewhat crystalline, have but indistinct bedding, and differ quite materi- 

 ally from the Paleozoic strata seen elsewhere in the vicinity. A thickness 

 of between 200 and 300 feet is exposed in an area whose boundaries can 

 not be closely defined owing to the overlapping- rhyolite sheet and the pre- 

 vailing mantle of drift, but the sedimentary rocks certainly cover the high 

 ground east of the wagon road. 



North of Lamar River the western slopes of Bison Peak show well- 

 bedded, dark-colored basic volcanic breccias, separated from the gneissic 

 hill lying between Slough Creek and Lamar River by a well-marked depres- 

 sion which defines the boundary line between the two rocks. The gneiss 

 is overlain at the highest point on this boundary line by a bed of quartzite, 

 which is of the usual pink and white variety, dipping 5° S., the strike 

 being N. 12° W. This quartzite makes a cliff 25 to 40 feet high, that 

 rises abruptly above the lakelet found upon the divide. The rock is gen- 

 erally somewhat fissile, well bedded, and of the normal character of the 

 Flathead quartzite. 



SLOUGH CREEK. 



The valley of Slough Creek above the confluence of Buffalo Creek 

 presents the picturesque scenery characteristic of this part of the Snowy 

 Range. The broad meadow lands which cover the valley bottom are flanked 

 by gentle slopes, with scattered groves of aspen and pine, above which are 

 the bold cliffs of white limestone that separate the lower slopes from the 

 crags of somber-colored breccias which form the upper part and summit of 

 the mountains. This valley presents the best exposures of the lower Paleo- 

 zoic series to be found in this part of the Park, and the general section of 

 the sedimentary rocks of the range which has just been given is compiled 

 from observations made in this valley and in the cliffs of the neighboring 

 valley of Soda Butte Creek. 



In the lower end of Slough Creek Valley the slopes on either side 



