NOirni SIDE OF ilOUSESLlOE GULCH. 157 



sideiable outcrop of White Porph)iv, whose thickness may be estimated 

 at 200 feet. Within tlie White Porphyry is u dark porphyry, very much 

 altered, but siniihir in appearance to the Sacramento Porphyry, and which 

 may once liave been connected with the body of this rock ah-eady described 

 above the Sacramento mine. These are succeeded by the Blue Limestone, 

 whose beds, as shown in the section and sketch, curve up and cover, some- 

 what irregularly, the double-pointed ridge over the arch of the fold. From 

 this limestone well-preserved specimens of Spirifera Rochymontana were 

 obtained. In the Blue Limestone on the crest of the arch are, according to 

 Professor Lakes, numerous vertical cracks, which may be cross fractures 

 I'esulting from folding. The lithological character of the Blue Limestone 

 varies greatly in different portions. Black chert concretions, which are as 

 elsewhere most frequent at its summit, are also found well down in the for- 

 mation. Many of the beds, especially near the base, are comparatively 

 light-colored. No satisfactory continuous section was obtained of the lower 

 Paleozoic beds, though the estimate of their aggregate thickness does not 

 vary from that obtained elsewhere. At various points an included bed oi 

 White Porphyry, near the top of the Lower Quartzite, and averaging about 

 thirty feet in thickness, was observed. The Archean is composed of gneist 

 and of red porphyritic granite with large orthoclase crystals. 



On the eastern slope of the anticline, outcrops of beds above the Blur 

 Limestone are exposed in the forest- covered region near the road leading 

 from East Leadville to Spring Valley, where they are much obscured by 

 surface accumulations, and, on the steeper slopes, by the relics of a lateral 

 moraine. Above the Blue Limestone the White Porphyry can first be distin- 

 guished ; next is an interval of coarse sandstone ; then a body of Sacra- 

 mento Porphyry, which apparentl}' thins out rapidly to the southward. 

 The White Porphyry, on the other hand, rapidly thickens in that direction, 

 as shown by its section on the eastern slope of Sheep Mountain. 



An attempt was made by Professor Lakes to obtain a continuous sccticm 

 fruni here eastward, through Faii-j)lay, across the upper members of the 

 Carboniferous and the overlying Triassic, Jurassic, and Cretaceous beds. 

 The result was not very satisfactory, inasnnu'h as a great portion of the 



