rSElJDOMORPniC SKRPENTINR. 123 



remain embedded in serpentine, and these grains show outhnes differing 

 essentially from those of" deformed crystals or clastic fragments, Ijnt resem- 

 bling in all respects corroded masses. Cracks in such fehlspars are also 

 filled witii serpentine, and it is manifest nnder the microscope that feld- 

 spathic material has been removed from the walls of these cracks, so that 

 they would no longer (it were they brought together. This evidence is of 

 exactly the kind connnonly accepted as proving the attack of other min- 

 erals. In one instance the phenomena are still more conclusive. In a slide 

 from Sulphur IJank (specimen No. 107), a feldspar shows such a crack nnich 

 widened, and, from the serpentine mass occupying it, sharp, elongated teeth 

 of serpentine bite into the clear f(ddspar. It is Impossible to explain such 

 a case otherwise than as an actual conversion of the feldspathic material 

 under the action of corrosive solvents. The sorpentine is characteristic and 

 unmistakable. The feldspar is unstriated, but probably triclinic. Other sat- 

 isfactory occurrences show that both plagioclase and orthoclase are converted 

 into serpentine. 



Fig. 4. Clastic quaitz partially oonvcrteil to sciiieiitiuc, wliich penetrates from the ontsido in needles. The specks irithin 

 ilic iinaitz are iluid inehisions and the strai;^ht prism is a small apatite. Magnifieil 53 diameters. 



That quartz is sometimes converted into talc is well known In the 

 altered sandstones of the Coast Ranges it is converted into serpentine. 

 This is shown, exactly as in the case of feldspar, by the presence, in patches 

 of serpentine, of irregular grains of quartz with corroded surfaces A 

 very beautiful case of the conversion of quartz to serpentine occurs in 

 altered sandstone from Clear Lake (specimen No. oT), and is illustrated 

 in Fig. 4. A clastic quartz grain of characteristic form, full of fluid inclu- 

 sions, containing an embedded apatite microlite, and behaving as usual in 

 polarized light, has been attacked from the outside. The exterior of the 



