80 QUIOKSILVIOR DEPOSITS OF THE PACIFIC SLOPE. 



boiling, conceiitratetl clilorliydric acid, yielded a solution containing both 

 alumina and magnesia. Clinochlor is thus absent. None of the specimens 

 affords an 0[)portunity of isolating the chlorite in sufficient quantities for 

 quantitative analysis. Pennine is stated to occur characteristically m hexag- 

 onal scales, which are readily attacked by chlorhydric acid.^ It is possible that 

 the rather rare irregular foils mentioned above belong to this species; but the 

 ril)rous variety is certainly not easily attacked by the acid. Of the ordinary 

 chlorites there remains only the ripidolite of Rose, which is Werner's chin- 

 rite and Dana's prochlorite. It is to be hoped that the researches of Pro- 

 fessor Tschermak will make future determinations more satisfactory than this. 

 Epidote. — Epidote is not very abundant in the metamorphic rocks. In 

 a single specimen, how^ever (No. 110, Knoxville), it is developed in large 

 crystalline grains with two cleavages, and in this case greatly resend^les 

 augite. The optical reference of this specimen was confirmed by a silica 

 determination, which was 38.98 per cent. The usual occurrence of this 

 mineral is in crystalline aggregates in association with chlorite, to which it 

 often stands in relations strongly suggesting epigenesis from chlorite. No 

 cases so fine as those described and figured in my memoir on the Comstock 

 lode were met with. Professor Rosenbusch^ doubts my explanation of 

 those occurrences, believing that they are not of such a nature as to pre- 

 clude the "simultaneous formation of the two minerals. It is difficult to prove 

 absolutely that they were not formed at the same time, because of the lack 

 of persistent structure in the chlorite; yet, from the inspection of almost 

 numberless cases, it certainly appears that epidote needles pierce aggre- 

 gates of chlorite fibers freely, while the ari-angement of these fibers does 

 not bear any visible relation to the epidote crystals such as is familiar in 

 cases of simultaneous formation. When I first expressed my opinion on 

 this subject I was unaware that other lithologists had reached the same 

 conclusion. Both Dr. H. Francke and Prof A. Renard anticipated me in 

 what I still regard as the most probable explanation.^ 



' Fouque and MiclielL(!vy : Miii. micrograpliique, p. 438. 



^Neues Jahrbuch fiir Miueral., vol. 2, 1884, p. 187. 



' Dr. Francke's paper, Stiiilieuiiber Cordillereiige.steine, Inaug. Diss., Leipzig, 1675, I have not seen. 

 The following is an extract from Mr. Renard'spaper on the diabase of Challes (Bnll. Acad. roy. Bel- 

 giqne, vol. 46, No. 8, 1878, p. 230-) : "Francke admits that tlie epidote is formed by the decomposi- 

 tion of the viridite included in the feldspars, the viridite itself arising from the decomposition of horn- 



