Washington — Igneous Rocks from Eastern Siberia. 175 



Art. XV. — Igneous Rocks from Eastern Siberia; by 

 Henry S. Washington. 



The rocks which form the subject of the present paper 

 were collected near East Cape in Siberia, during the summer 

 of 1900, by Mr. A. G-. Maddren, who, through the kind offices 

 of Dr. L. B. Bishop of ]New Haven, generously sent them to 

 me for investigation. It is a pleasure to record my thanks to 

 both these gentlemen for the interesting material thus made 

 available for study, and which has added another to the grow- 

 ing list of localities of foyaite and related alkalic rocks. 



East Gape. 



Foyaite. — The most interesting rock of the suite is one —the 

 only one— from a locality given as " South of Whalen or 

 Itschan, East Cape." As the locality is little known, it may 

 be of interest to quote from a letter received from Mr. 

 Maddren. 



" The region in the vicinity of East Cape is a rugged one. 

 Mountainous ridges of crystalline rocks come out to the sea- 

 shore and form bold, rugged cliffs five to eight hundred feet 

 in height. Between these ridges are low swampy stretches of 

 tundra, with pebble beaches. The tops of the ridges are 

 almost barren of vegetation, and the surface is overstrewn 

 with frost-broken blocks of the country rock of all sizes and 

 shapes." 



The rock is quite coarse in grain, cqui posed very largely of 

 an alkalic feldspar, with less nephelite of a slightly brownish 

 color. Scattered through these are small (up to 5 mm ), stout 

 prisms of hornblende, the arrangement of which suggests a 

 schistose structure. Minute specks of purple fluorite are also 

 visible with a lens. 



Under the microscope the feldspar is seen to be distinctly 

 tabular, in stout individuals, generally twinned according to 

 the Carlsbad law. They show little, if any, microperthitic 

 development, or the moiree appearance so characteristic of 

 soda-rich orthoclase, and it may be inferred that the feldspar is 

 nearly pure orthoclase. The nephelite occurs in stout indi- 

 viduals, xenomorphic toward the feldspar tables. 



Interstitial between these feldspars and nephelite areas, but 

 varying much in relative amount in different parts of the sec- 

 tions, is a finely granular, colorless substance, of low refractive 

 index, the irregular grains, between crossed nicols, being either 

 isotropic or showing yellow or orange colors of the second 

 order, and optically positive. This mineral cannot be cancri- 



