176 Washington — Igneous Rocks from Eastern Siberia. 



nite, as was thought at first, since this is optically negative, 

 and the small amount of C0 2 shown by the analysis corre- 

 sponds to only 0*8 per cent of this mineral. As the analysis 

 also shows an excess of alumina, the granular material must be 

 regarded as.hydronephelite, especially as the appearance of the 

 aggregate agrees with the description by Diller of the hydro- 

 nephelite of Litchfield, Maine. * 



The hornblende, which is seen only rarely in the sections, is 

 of a dark olive-green, with very intense pleochroism. There 

 is also present, in less amount, a highly pleochroic, yellowish- 

 green biotite, in stout ragged individuals, which resembles that 

 of the Maine Litchfieldite described by Bayley.f 



The small grains of fiuorite are seen here and there in the 

 sections, the purple color being often intense and again very 

 faint. They are usually xenomorphic toward crystal faces of 

 the feldspars, almost never as inclusions in the latter. Small 

 zircons are fairly abundant, for such an accessory constituent, 

 and a few titanites were seen. One of these last includes a 

 minute, colorless, isotropic, well-shaped octahedron, of high 

 refractive index, the nature of which could not be ascertained. 





I. 



II. 



III. 



la. 



Si0 2 



.. 55-38 



53-56 



55-87 



•923 



Al O . _ 



.. 23-74 



24-43 

 2-19 

 1-22 



•21-82 

 2-34 . 

 1-10 



•233 



2 3 " 



Fe 



0-63 



•004 



FeO 



.. 1-26 



•018 



MgO. 



_. 0-81 



0-31 



0-48 



•020 



CaO 



.. 0-67 



1-24 



3*07 



•012 



Na 2 _. 



.. 5-29 



6-48 



4-81 



•085 



K 2 



._ 10-05 



9-50 



10-49 



•107 



H 2 110°+... 



._ 1-12 



0-93 



0-34 





H 2 110°-. .. 



.. 0-38 













co 2 



.. 0-05 













Ti0 2 



. . trace 











ZrO 



. . 0-06 













PO 



_. 0-06 





so 3 ._ 



.. 0-07 





CI 



. _ trace 













MnO 



. _ trace 



o-io 



trace 





BaO 





— 









99-57 99-96 100-32 



I. Foyaite, East Cape, Siberia. H. S. Washington anal. 



II. Nephelite-syenite. Beemerville, N. J. L. G. Eakins anal. 

 J. P. Iddings, Bull. 150, U. S. G. S., p. 211, 1898. 



III. Leucite-phonolite. Lake Bracciano, Italy. H. S. Wash- 

 ington anal. Jour. Geol., vol. v, p. 49, 1897. 



la. Molecular ratios of 1. 



* J. S. Diller, this Journal, vol. xxxi, p. 266, 1886. 



f W. S. Bayley, Bull. Geol. Soc. Amer., vol. iii, p. 236, 1892. 



