

_. , _ v .....„._.... ..._.„. _~_^_, „„_ _.._.♦,- — — . T „_ — .__ --,.-- . — ~, — , — _.„„._ ._ ~*. F ,^. v .^^„^ l . k *y v .. „„^., :v ,. f ^ *■*. | ■^^■■■i^h ■ bb^i 



224 



THE AUEIFEROUS GEAVELS OF THE SIERRA NEVADA. 









above Newtown on the South Webber Creek, is the locality of the so-called 

 " photograph rocks " or u picture rocks/' which were exhibited in San Fran- 

 cisco some years ago, and which w r ere supposed by some to be natural photo- 

 graphs of the surrounding scenery of the locality where they were obtained. 

 These " photographs " were dendritic markings on a large scale, and they 

 seemed to penetrate the whole mass of the rock, which was itself a pretty 

 fine sandy and clayey material, horizontally stratified and in places very deli- 

 cately and thinly bedded. The materials of which this rock is composed 

 seem to be partly at least of volcanic origin, and the hill in which they occur 

 is capped with a heavy mass of white lava. Infusorial material has also 

 been obtained here and sold in San Francisco, under the name of "El Do- 

 rado polish/' The greater portion of the dendritic markings occur in hori- 

 zontal bands parallel with the bedding of the material and from a fourth of 



- 



an inch to two inches wide. These bands usually have a dense black border 

 on the upper and lower margin, and between these borders is a narrow medial 

 band of white ground mottled with the dendritic markings, which are often 

 extremely varied and elaborate, forming two lines of " landscape-scenery/' as 

 these markings are called, the one being upright and the other inverted. 

 These curious markings are sometimes continuous for fifteen or twenty feet. 

 Between the bands of dark variegated material the rock is white. These 

 markings are not merely superficial, but penetrate the mass of the rock. The 

 bands do not always run horizontally, but occasionally rise and fall in wavy 

 lines, or are developed in rather complex convolutions, although the bed- 

 ding of the rock itself is everywhere nearly horizontal. In one portion of 

 the bank the color of the mass of the material is a pretty deep and brilliant 

 pink, instead of white as usual. This portion also is traversed by markings, 

 which, however, do not so often assume the form of bands, but are rather 

 irregular although often extremely beautiful. 



There are two points here, on about the same level, and within a hundred feet 



* 



or less of each other, at which some little quarrying has been done. One of 

 these openings yields fine specimens of the dendrites, but none of the " pol- 

 ish" of good quality ; the other opening yields both. The passage from one 

 material into the other is gradual, and there is no well-defined line of demar- 

 cation between them. These openings are small and do not offer facilities 

 for thoroughly investigating the geology of the locality. The hill rises to a 



■ 



height of several hundred feet above the quarries, and appears to be made 



up of u white lava, 



>> 



that is, of white, consolidated, volcanic ash. These are 



