54 



GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Section of the Mesozoic sedimentary rocks exposed in Cinnabar Mountain, etc. — Cont'd. 





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to 





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V i 



° j 



2 



^ s 





S 



V 



Q 







U 



1 



Quartzite changing to sandstone, light gray, dense in texture, and forming a prominent 

 wall 15 to 20 feet wide 



Limestones, blue-gray in color but weathering to a creamy buff tint on the surface. The 

 rock is dense in texture and shows the remains of the same gasteropoda found in the 

 beds of Little Quadrant Mountain. In the Cinnabar section this intermediate horizon 

 includes a portion of the thickness given to the Dakota conglomerate, but it is char- 

 acterized by red magnesian limestones which possess many characters similar to those 

 of the volcanic ash beds found farther north above the Dakota conglomerate, and 



passing into sandy shales which are capped by 10 feet of quite pure limestone 



^Dakota conglomerate and sandstone 



{ Reddish shales and impure limestones - 



Limestones and calcareous sandstones, occasionally a conglomerate; carries an abun- 

 dance of fossil remains, which are generally fragmentary near the base 



Red argillaceous shale 



Gray calcareous shales and impure limestones, characterized by an abundance of fossil 

 remains, particularly in the upper strata. The beds are separated near the center by 

 oolitic limestones 



Green and red shales 



Sandstone, saccharoidal in texture, generally light gray or buff in color, but red or brown 

 on weathered surface 



Red beds, consisting of very fissile sandstones and impure arenaceous clays 



Limestone, compact in texture, gray in color, and carrying remains of liuguhis 



Limestones, dark gray in color, generally fetid, often arenaceous, and frequently char- 

 acterized by rod-like masses of chert, which are seen to consist of grains of sand 



embedded in the siliceous matrix, the concretions having a white chalky surface 



[ Quadrant quartzites. 



Feet. 

 50 



175 



85 



75 



8 



132 

 50 



50 

 75 

 20 



125 



The western face of Electric Peak shows a number of sheets of igneous 

 rock, varying from 5 to 50 feet in thickness; but no dikes, either vertical 

 or inclined, were observed on this side of the mountain. The western 

 summit consists of a sheet of andesite-porphyry several hundred feet thick. 

 In the eastern spurs of the mountain numerous vertical and inclined dikes 

 cut the upturned beds. Those on the southeastern spur trend to the south- 

 west and northeast. They also traverse the eastern summit of Electric 

 Peak. The southeastern spur of the mountain shows steeply upturned 

 sedimentary beds, which at the base are overthrown and reversed. This 

 spur probably consists of a synclinal fold which was accompanied by 

 faulting, the eastern limb, forming the lower portion of the spur, having 

 a nearly vertical position. The axis of the syncline has a trend to the 

 southwest and northeast. The overthrown beds at the southern extrem- 

 ity of this spur show Madison limestones, Quadrant quartzites, and the 

 regular sequence of overlying Mesozoic strata. The beds strike north, 

 and they dip from 50° to 70° E. The Gardiner River cuts across the 



