74 BUEEAU OF AMERICAN ETHNOLOGY [bull. 52 



quartz and different varieties of plagioclase, ranging from oligoclase 

 to basic labradorite, and occasional grains of pyroxene. Superficially 

 the red portion of this specimen resembles the baked earths, but 

 closer examination has shown it to be distinctly different. Its glassy, 

 vesicular texture throughout is indicative of melting; the red colora- 

 tion may be the result of alteration or oxidation, whereby magnetite 

 has been changed to the red oxide of iron. It seems probable from 

 this evidence alone that the whole of the present specimen represents 

 an originally vesicular rock in the red part of wliich the iron is in 

 a more higlily oxidized state than in the dark-gray part. 



No. 263728. Specimen label. ''Locality: 3 miles north of Mira- 

 mar. Bluff on the coast, 5 feet helow the top in Ameghino's, 'Ensena- 

 dean.' Material: Scoria and adjacent loess." 



This specimen is an irregular, slaglike piece of scoria, consisting of 

 a dark, olive-green glass, almost pumiceous at certain points and 

 filled with vesicles wliich are often so large and numerous as to leave 

 only thin walls of the glass between them. The outer surface of this 

 scoria has plainly been in contact with the loess, some of which stiU 

 clings to it and is of a light-brown color. The division between the 

 scoria and the loess is sharp and there is no indication of a transition 

 between the two. In the cavities of the scoria there is an accumula- 

 tion of rounded grains of magnetite, olivine, quartz, and plagioclase, 

 measuring up to 1 mm. in diameter. These have reached their pres- 

 ent position either by wind or by water action. Microscopicall}" this 

 scoria is similar to specimen 263725. Angular and rounded frag- 

 ments of quartz, plagioclase, and pyroxene are set in a streaky, 

 brownish glass out of which lath-shaped microhtes, showing high 

 extinction angles and medium birefringence, have crystallized; these 

 are probably pyroxene. The refractive index of the glass is not con- 

 stant, but ranges from about 1.515 to 1.55, and occasionally shows 

 birefringence resulting evidently from strain. 



The brown earth surrounding the scoria is of the usual type and 

 consists chiefly of argillaceous material, fragments of plagioclase, 

 quartz, pyroxene, and magnetite. Volcanic glass is less abundant 

 than usual. 



Part of the scoria was heated to 1 ,240° for 1 hour and then held at 

 1,000° for H hours. Under this treatment it melted down to a dark, 

 brownish-green glass, in which many of the original mineral frag- 

 ments (quartz, plagioclase, and p}Toxene) were stUl ^^sible. Newly 

 formed microlites of high refractive index, medium to fauiy strong 

 birefringence and parallel extinction, were also abundant, but were 

 too fine for satisfactory determination. Occasionally radial aggregates 

 of a lower-refracting, medium to weakly birefracting, substance were 

 observed, which may have been plagioclase feldspar. Particles of 



