NORTH WALL OF HORSESHOE GULCH. 155 



tlic- (lark oiitrrop is .simply a portion o^" the Jjlue Limestone left above it at 

 this point, the main mass beinii" represented by the line of Blue Limestone 

 along the southwest base of the ridge. The thickness of the porj)hyry 

 bodv, as represented by the distance between these outcrops, may be 

 roughly estimated at al)oiit six luuulred feet at the south end and 1,000 to 

 1,500 under the summit of the ridge. It seems evident, therefore, that we 

 have here in actual outcrop a portion of the main laccolitic mass as it ascended 

 from below across the lower Paleozoic beds and spread out above the hori- 

 zon of the Blue Limestone, as is shown theoretically in Section F. 



Li the shales and quartziles on the northern and eastern slopes of White 

 Ridge are numerous bodies of White Porphyry, which in the neighborhood 

 of the summit sometimes seem to ramify and intersect the beds, but in 

 general show a tendenc}- to spread out between them. As it was impossi- 

 ble to delineate all the varying outlines of these bodies, the prevailing form 

 alone has been shown on the map, viz, that of intrusive sheets spreading 

 out from the main laccolitic bod}- along the stratification planes and grad- 

 uallv thinning as they depart from it. 



North wall of Horseshoe gulch. — The sectiou taken aloug the soutli face of the 

 ridge east\^•ard from the outcrop of Blue Limestone is approximately as fol- 

 lows: A covered gap of about three hundred feet, containing, as is shown 

 higher up, a bed of 50 feet of White Porphyry directly above the Blue 

 Limestone; then about one hundred feet of shales, both calcareous and 

 silicious, but mainly quartzite and sandstone; then a second bed of White 

 Porphyry 50 feet in thickness, 5 feet of quartzite, and 5 feet more of White 

 Porphyry; then varying quartzites, micaceous sandstones, and shales, above 

 A\hich are fine black shales, carrying pyrites and some fossils, from which 

 Avere obtained the foUowintJ- forms: 



Product us ticmintieulatus. 

 J'r(i(luctu)imuricafus=P. longispinus Meek. 

 I'roductus vuru. 

 Prinluctuii ohslatus. 

 Proiluvtun jxTlcn uis. 



ISpiri/i r camcratua. 

 Spirifer, sp. ! 



Avicvlopecten carboniferus. 

 FenesteUa, sj). uudet. 

 Ehombopora, sp. f 



Grijffiihides, sp. uiulet. i Fragmeuts of crinoids and bryo^oan>i. 



The above succession of beds, which is taken from notes by Professor 

 Lakes, represents approximately what has been assumed as the Weber Shale 



