36 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



LITTLE QUADRANT MOUNTAIN AND FAWN CREEK VALLEY. 

 LITTLE QUADRANT MOUNTAIN. 



North of Quadrant Mountain is another flat-topped elevation, known as 

 Little Quadrant Mountain, which is clearly defined from the adjacent moun- 

 tains by the deeply incised valleys of Fawn Creek and the headwaters of the 

 Gardiner. The mountain is carved out of a block of Mesozoic strata, into 

 which numerous sheets of andesite-porphyry, offshoots from the Gray Peak 

 intrusion, have been injected. The resistant nature of these intruded sheets 

 has produced the marked terracing' which now forms so characteristic a 

 feature of the southern slopes. The following section, made by Mr. 

 George M. Wright, represents the beds exposed on the southern side of 

 the mountain, the lowest strata being the brecciated limestone forming the 

 top of the Madison limestone series, through which Fawn Creek has cut a 

 small canyon at the forks of the stream: 



Section of beds exposed on south side of Little Quadrant Mountain. 



Num- 

 ber. Feet. 



( 4 Sandstone 20 



Interval with no exposure (broad bench about 300 yards wide) 75 



Mica-hornbleude-andesitc-porphyry 50 



3 Cherty, arenaceous, and calcareous beds : 



Limestone 2 



Interval with no exposure 35 



Cherty, arenaceous, and calcareous beds 40 



Teton 

 limestone. 1 



77 



Quadrant 

 quartzite. 



2 Sandstone and limestone : 



(6) Limestone, white, much of it brecciated and mixed up with 



sandstone 20 or 25 



(a) Sandstone 175 



200 



Interval with no exposure 100 



Madison ( 1 Brecciated limestone, having some layers compact, not brecciated; iu walls of 

 limestone. ( miniature canyon at junction of branches of Fawn Creek 40 



The total thickness of this section is not given, owing to the uncer- 

 tainty of the exact thickness of two of the intervals above mentioned. 



Above the beds of the section just noted there is a long steep slope, 

 rising 300 feet or more to a prominent cliff formed of the Ellis sandstones. 



