420 



J U LIEN 



indicate a proportion of nearly 30 per cent, of brucite. His 

 specimen was of the usual " dull yellowish green, inclining to 

 olive" ; specific gravity, 2.82.^ 



3. Condition of the iron oxides, whether as hematite, magne- 

 tite or combined in a silicate. Only a trace of hematite or free 

 iron ochre was found in the thin sections. On digestion of 

 half a gram of the finely pulverized rock in boiling saturated 

 solution of citric acid, it was dissolved in a deep yellow solution. 

 The small grayish residue of gelatinous silica, treated with hot 

 solution of potassium hydrate, yielded traces of undissolved sili- 

 cates (diallage, bronzite and talc), chromite and magnetite. 

 The last was separated by a strong bar magnet, with apparently 

 no disturbance of the feebly magnetic chromite. It thus be- 

 came evident that the ferric as well as the ferrous oxide was 

 present in that form in the diallage molecule, as illustrated in 

 many analyses of pyroxene recorded by Dana, who reports 

 " certain varieties containing the trivalent metals, aluminum, 

 ferric iron and manganese. These varieties may be most simply 

 considered as molecular compounds of Ca(Mg,Fe)Si20g and 

 (Mg,Fe) (Al,Fe).,SiO,., as suggested by Tschermak." 



Mineralogical Constitution of the Scrpentinoid. — Instead of the 

 predominance of serpentine in our rock, the chemical and micro- 

 scopical evidences suggest rather an admixture of hydrated forms 

 of ferromagnesian minerals, such as those of which analyses, 

 chiefly from American localities, are tabulated below in the 

 order of increasing amounts of lime. 





Olivine. 



Villarsite. 



Asbestus. 



Actinolite. 



Tremolite. 



Diallage. 



Sahlite. 



SiOj 



Al,(), ... 



FeO 



MnO ... 



40.75 

 936 



38.90 

 7.80 



55.20 



11.82 



56.30 

 1.70 



4-30 



57.40 ' 

 .40 



1.40 



51-41 

 4.32 



9-31 



.04 



53-12 

 1.06 

 6.01 



.60 



CaO 



— 



— 



— 



10.70 



13.90 



20.60 



23.62 



MgO 



H2O 



50.28 



100.39 

 Manice. 



47-50 

 5.80 



100.00 

 By theory. 



30.73 

 2.25 



24.00 

 1. 00 



24.70 

 .40 



98.20 

 C. F. Ram- 

 melsberg. 



15-14 



14.50 

 -47 



Analyst. 



100.00 

 Beck. 



98.00 

 Seybert. 



100.82 

 W. G. Brown. 



99-38 

 Bowen 



^Nuttall, Am. Jour. Sd., IV, 1822, 16-17. 



