84 BUREAU OP AMERICAN ETHNOLOGY [bull. 52 



pebbles of various colors (white, gray, red, brown, and black) are 

 scattered. These pebbles range from 1 mm. to 1 cm. in diameter and 

 are more or less rounded and distinctly water-worn. They appear 

 to be in large measure quartzose and cherty in character. Under the 

 microscope much argillaceous material was observed. The sand 

 grains consist largely of plagioclase and quartz, both stained or 

 coated with iron oxide. Isotropic glass, usually considerably altered, 

 is present in noticeable quantities. Minor components are pyroxene, 

 magnetite, and spinel (or garnet). Many of the pebbles consist of 

 quartz which appears to be vein quartz. Other pebbles are com- 

 posed of chalcedony of typical fibrous structure. The dark-red and 

 brown pebbles contain so much fine iron oxide as to be practically 

 opaque. They contain either quartz or chalcedony and resemble 

 ferruginous chert in general appearance. 



This specimen crumbles into a muddy sand when immersed in water. 

 Its water solution gives a noticeable chloride reaction when tested 

 with silver nitrate. 



No. 263743. Specimen label. ''Locality: Monte Hermoso near 

 the old ligJithouse. Material: Volcanic ash from the Puelchean." 



V light-gray, gritty material of fine even grain which microscopi- 

 cally consists largely of colorless volcanic glass, the refractive index 

 of which is fairly constant and averages about 1.500. Some argilla- 

 ceous material is present, as are occasional grains of plagioclase and 

 quartz. After washing away the major part of the glass, grains of 

 plagioclase, quartz, hornblende, pyroxene, biotite, magnetite, apatite, 

 zircon, spinel (or garnet), and epidote were found in the concentrates. 



This ash crumbles but little in water. Its water solution, when 

 tested with silver nitrate, gives an abundant silver chloride precipitate. 

 The chlorine is evidently present in sodium chloride. 



SPECIMENS FROM RIO COLORADO 



Nos. 263730, 263739. Specimen labels. "Locality: Delta of the 

 Rio Colorado, 100 miles south of Baliia Blanca. Material: 'Tierra 

 Cocida,' or hurnt earth, produced hy burning the 'esparto,' a ranJc grass 

 growing in swampy ground. Area burnt about ^ acre. Earth all burnt 

 to tender crusts to a depth of 3 to 5 inches.^' 



These specimens are brick-red in color, fine-grained and indurated. 

 They are full of irregular holes and cavities and carr}^ numerous 

 impressions of grass leaves. Under the microscope numerous frag- 

 ments of quartz, plagioclase, pyroxene, magnetite, colorless volcanic 

 glass, and abundant argillaceous material deeply impregnated with 

 iron oxide are visible. Except for the red oxide of iron, this compo- 

 sition is similar to that of the original loess from which these burnt 

 earths were derived. Microscopically this burnt earth resembles 



