Ellis 

 limestone 



fa:n t pass. 49 



soil. The saddle itself is formed of limestones broken through bv andesite- 

 porphyr y. The following section shows the series of beds exposed from the 

 pass to the summit of the peak to the north : 



Fan Pass section. 



Num- 

 ber. Feet. 



Dakota. 8 Dakota conglomerate and sandstone; creamy, pink, broken through by an- 



desite porphyry 40 



( 76 Limestone, hard, gray, crystalline, weathering brown 10 



la Limestone, granular, arenaceous, light drab 15 



Ellis , 6 Limestone, more or less arenaceous in certain bands, fossililerous. Strike, 



sandstone. 1 N. 45° W. ; dip, 25° N 75 



56 Limestone, soft and sandy 10 



5a Limestone, arenaceous, gray-brown 5 



I" 46 Red shale, crumbly and soft 8 



4« Slate; metamorphosed by andesite-porphyry 2 



Andesite-porphyry. 



3 Limestones, soft, crumbly, very argillaceous, with harder crystalline layers; 



very fossil iferous _ 58 



2 Limestone, finely crystalline, weathers brown, somewhat shaly 5 



1 Limestone, shaly, broken through by andesite-porphyry 45 



To the east of Fan Pass an extension of the anticlinal uplift noted 

 to the west brings up the red shales and sandstones from the upper portion 

 of the Teton formation. From the summit of the mountain peak north of 

 Fan Pass the ledg-e extends in a northwest direction until it meets the lone: 

 southwestern spur of Electric Peak. The Dakota conglomerate forms the 

 crest of the ridge as far as the second peak north of Fan Pass, and, as 

 already noted, the same rock extends westward, forming the crest of the 

 encircling ridge The summit of the second peak north of Fan Pass is 

 formed of andesite-porphyry. This rests upon Dakota conglomerate and 

 is overlain by cherty limestone, which is apparently part of the Dakota 

 limestones, but is of different habit and carries light greenish-yellow chert. 

 Between this point and the 10,100-foot peak to the northeast a succession 

 of beds is exposed in which the shales are cut by intrusive sheets of 

 andesite-porphyry. The Dakota limestone, somewhat metamorphosed, but 

 showing the crystalline marks and the little gasteropod shells so character- 

 istic of this horizon, is overlain by very splintery greenish-yellow shale, 

 weathering brown. This in turn is capped by a baked sandstone about 20 

 feet thick, which is overlain by the upper quartzite belt of the Dakota 

 series, the bed being here 30 feet thick. The carbonaceous shales of the 

 Benton formation form the ridge from this point eastward to the slopes of 



MON XXXII, PT II 4 



