160 



GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Survey Peak section. 



Sum 

 ber. 



Teton 18 



Quadrant ... 17 



(16 





15 





14 





13 





12 





11 



Madison 



10 





9 





8 





6 















3 



Three Forks? J 



2 





1 



Feet. 



Clierty sandstone, forming slopes of Survey Peak. 

 Quartzite, white, etc., forming summit of peak. 



Limestone, with red streaks, etc., near top 1, 000-J^ 



Limestone, gray, splintery 25 



Limestone, brecciated 50 



Limestone, gray, similar to beds below 50 



Limestone, brown, containing peculiar chert balls 10 



Limestone, cherty, fossiliferous, steely gray 300 



Limestone, gray, weathering brown, with smooth surface 30 



Limestone ; not exposed , 25 



Limestone, gray brown, obscure traces of fossils 30 



Limestone; not exposed .30 



Limestone, deuse, gray 10 



Limestone, brown, with rough, guttered surface. Strike N. 5° W. ; dip 



30° W 100 



Limestone, light yellowish green; laminated 10 



Limestone, light gray, cherty 25 



Limestone, dark gray, cherty. Strike N. 10° E. ; dip 5 3 AV 10 



Limestone, great ledge of rough brecciated rock at base of east slope of 



the peak 150 



The summit of Survey Peak is formed of the cherty sandstones which 

 occur at the base of the Teton formation, but the Avestern flank of the 

 mountain is coA~ered by a narroAv strip of rhyolite that connects the rhyolite 

 sheet near the head of Berry and Conant creeks with the rhyolite plateaus 

 Avhich sweep northward to the geyser basins. This rhyolite AA^est of the 

 peak is about one-fourth of a mile Avide, its upper limit being 8,600 feet, 

 and it forms a bench terminated westward by bold cliffs, some 200 feet in 

 height, that form the wall of the Boone Creek amphitheater. The bottom 

 of the sheet dips to the Avest. The surface of the rhyolite is quite irregular, 

 as the sheet rests upon the steeply upturned Teton shales which have 

 slipped beneath its weight, forming great fissures of varying width, from a 

 few feet to many yards across and often many yards long. Huge masses 

 have become detached and have slid down to the bottom of the amphi- 

 theater valley. To the south the rhyolite thins out against the cherty 

 sandstones, but on a projecting point extends to the flat summit at the head 

 of Berry Creek. Beneath the rhyolite the walls of the amphitheater show 

 the red Teton shales and sandstones well exposed and dipping steeply to the 

 nortliAvest, These Teton sandstones probably extend under the gravel- 

 capped ridg-e to the west, but no exposures Avere seen. 



