SHEEr MOUNTAIN. 165 



fault on the west are always found to stand at a nearly vertical angle. The 

 Lamb Mountain laccolite, it must be borne in mind, is at a higher horizon 

 than the main sheet of White Porphyry. It may be an irregular offshoot 

 from the AVhite Ridge laccolite, or, as shown in Section G, simply an extru- 

 sion from the main sheet. 



Sheep Mountain. — Sheep Mountain itself is an important peak, having an 

 elevation of over two thousand feet above the bed of the gulch and form- 

 ing the northern culmination of a ridge running in a nearly northwest and 

 southeast direction, whose form is closely connected with its geological 

 structure, since the line of fiiult south of Sheep Mountain follows approxi- 

 mately its crest. The internal structure of the peak is best exposed on the 

 north face, a view of which is shown in Plate XVIII. The eastern slope 

 of Sheep Mountain is a little less steep than the dip of the beds, for which 

 reason the White Porphyry which crowns its summit is denuded over a con- 

 siderable portion of the slope, and comes in again at the foot, where the 

 slope becomes more gentle. The western side of the fold, as shown in the 

 sketch, is very nearly vertical In point of fact, however, the angle is a 

 little over the vertical, or, in other words, the beds dip slightly east, as 

 shown in section G. This is not apparent, however, on the cliff, from the 

 fact that its plane is not exactly at right angles with the axis of the fold. 

 Here, again, as in the Sacramento arch, the series of beds when vertical 

 appear thinner than when standing nearly horizontal ; in other words, they 

 seem to be compressed between the arch of the fold and the plane of the 

 fault, which is not at all impossible or even improbable. Unfortunately, it 

 could not be determined b}' actual measurement, as there was no continu- 

 ous outcrop of the vertical beds. 



A section was carefull}' made across the beds from the crest of the fold 

 to the summit of the peak by Mr. Cross, from whose notes most of the fol- 

 lowing data are taken. The Archean exposures are mainly of gneiss and 

 their bedding is comparatively distinct. As well as could be ascertained, the 

 beds stand nearly vertical and have an east and west strike, or at right 

 angles to the axis of the fold. Adjoining the vertical Cambrian beds was 

 noticed a little irregular dike of White Porphyry about four feet in thick- 

 ness, which comes out of the gneiss nearly parallel to the strike of the 



