22 



EDWIN C. ECKEL 



these green slates were probably derivedj a number of analyses 

 have been selected from Turner's papers ' on the rocks of the Sierra 

 Nevada, and these are presented below. The specimens analyzed 

 were all from California localities, but none, unfortunately, from 

 very near the El Dorado county slate deposits. None of the 

 analyses are complete, but sufficient determinations are given in 

 each case to permit their use for the present purpose — their 

 comparison with the analyses, given above, of the green slate from 

 Eureka Slate Co. quarry. The coincidence in general composi- 

 tion seems to be sufficiently marked to suggest, with a high degree 

 of probability, that the green slates have been derived from some 

 rock of type similar to those whose analyses are given in the 

 following table : 



ANALYSES OF IGNEOUS ROCKS OF THE MOTHER LODE DISTRICT, 



CALIFORNIA. 



Silica (SiOg) 



Alumina (AI2O3) and titanic oxide (TiOg 



Iron 0}{ides (FeO, FcgOg) 



Lime (CaO) 



Magnesia (MgO) 



Alkalies (KgO, NaaO) 



Carbon dioxide (CO2) ) 



Water \ 



45-92 



n. d. 

 n. d. 

 9.96 

 13.85 

 0.81 



n. d. 



1. Gabbro : east side of Eureka Peak, California; analyzed by Hillebrand and 

 Steiger. {Seventeenth Annual Report, U. S. Geological Survey, Part II, p. 642.) 



2. Diabase : north of Hornitos, Calif.; analyzed by Hillebrand. {Ibid., p. 694.) 



3. Augite porphyrite : west of Jackson, Calif.; analyzed by Hillebrand and Steiger. 

 {Fourteenth Annual Report, Part II, p. 473.) 



4. Augite porphyrite : Plumas county, Calif.; analyzed by Hillebrand and 

 Steiger. {Ibid.) 



5. Gabbro: east of Penman Peak, Calif.; analyzed by Hillebrand and Steiger. 

 {Seventeenth Annual Report, Part I, p. 642.) 



Summary of the evidence as to the origin of the green slates. — An 

 attempt has been made to obtain evidence from three distinct 

 sources as to the probable derivation of the green slates. One 

 of these possible lines of solution gave no evidence of value; the 

 other two, however, are apparently conclusive, 



' Fourteenth and Seventeenth Annual Reports, U, S. Geological Survey, 



