122 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



serpeutinized. The observer would incline to the belief that both methods 

 were followed, but the conclusion would not be certain, because many 

 rocks whicli are really liolocrystalline a])pear to the e\-e to be mere sand- 

 stones somewhat modified. It will be seen in the sequel that botli proc- 

 esses can be traced microscopically. 



The serpentinoid rocks invariably slio\v evidence of violent dynamic 

 action. Traces of stratification are often visible, but can never be followed 

 more than a few feet, and single croppings frequently exhibit remnants of 

 stratification in all sorts of contradictory directions. There is usually little 

 evidence of plication ; as a rule, the rock Avas reduced to a confused mass 

 of rubble prior to serpentinization. The blocks indeed wei-e often some 

 yards long, but even these were generally divided by numerous cracks. 



Microscopical evidence of derivation. While It IS UOt pOSsiblc tO folloW iu tllC field 



the transitions of the components of the altered rocks, the indications of 

 field observation were found to be borne out by microscopical and chem- 

 ical examination. It can be shown, as I think beyond dispute, that all of 

 the principal minerals of sandstones and granular, metamorphic rocks are 

 converted into serpentine, and the inference with regard to some of the 

 less important ones is also strong. After tlie investigations of the last 

 fifteen years, together with the earlier macroscopical examinations, it will 

 sm'prise no one to hear that in the granular, metamorphic rocks of the 

 Coast Eanges augite and hornblende are found passing into serpentine. 

 The attack takes place along the surfaces and cracks, exactly as in uraliti- 

 zation and chloritization, while the resulting mineral has all the distinctive 

 characteristics described in the preceding pages. Sometimes partial pseu- 

 domorphs may be observed in which a kernel of the bisilicate is embedded 

 in a mass of serpentine, surrounded by an outline characteristic of the par- 

 ent mineral. This, however, is rare, apparently because Avell developed 

 crystals of augite and hornblende are also rare. 



Though Bischof, vom Rath, and others have shown that the conver- 

 sion of feldspar to serjjentine was probable, I am not a^vare that it has ever 

 been conclusively proved. In the altered sandstones and the granular 

 metamorphics of the Coast Ranges, however, it seems beyond doubt that 

 this alteration has taken jilace. In vi-i-y numerous cases grains of feldspar 



