398 H. W. TURNER 



from the serpentine have soaked into the shale and deposited 

 their burden. 1 The above facts cannot be regarded as evidence 

 that the Bachelor lode has formed from the replacement of a soda- 

 feldspar dike, but it gives conclusive evidence that such dikes 

 readily undergo replacement when permeated by mineral waters. 

 The soda-feldspar dikes occur very often in association with ser- 

 pentine. This is the case in Plumas and Butte counties, where, 

 however, no evidence of mineralization was noted. It is also the 

 case at the Big Canyon mine, Eldorado county, and at the Wil- 

 lietta, Bachelor, Black Warrior, and Wheeler and Hill mines in 

 Tuolumne county, and at various points north of the Merced River 

 in Mariposa county. The dikes are not confined to the serpen- 

 tine, however, although, so far as I know, they are nearly always 

 in the neigborhood of this rock. One dike, however, more than 

 a kilometer in length was noted in the sediments of the Calaveras 

 formation, the nearest mass of serpentine being four kilometers 

 distant. Open cuts at numerous points indicated that this dike 

 had been prospected for gold. There is also a syenite dike in the 

 slates of the Mariposa formation by the tollhouse west of Princeton, 

 along which are small quartz veins. This dike is likewise mineral- 

 ized, containing lime carbonate very abundantly and pyrite. At 

 the Shaw mine also the dike is in slates, probably of Carboniferous 

 age. The usual association of the dikes with serpentine suggests 

 an original genetic connection, but this has nothing to do with the 

 mineralization of the dikes, which takes place irrespective of the 

 immediate presence or absence of serpentine, although it is pos- 

 sible that magnesium carbonate is never present to any extent 

 except when serpentine is immediately adjacent. The associa- 

 tion of gold with soda-feldspar dikes, so far as my observation 

 goes, is more frequent than with dikes of other rocks, and this 

 may point to albite being a mineral more readily altered or 

 replaced by mineralizing solutions than any other feldspar. 

 Experiments have been made on the relative solubility of some 

 of the feldspars in pure water and in water charged by carbon 

 dioxide. Mr. George Steiger kept for one month one half grain 

 1 For definite examples of this see Bull. Geol. Soc. Am., Vol. II, pp. 406-408. 



