58. BUREAU OF AMERICAN" ETHNOLOGY [bull. 52 



A loose, white, incoherent earth of even grain consisting in large 

 measure (about 90 per cent) of volcanic glass in angular and splintery 

 fragments, which often show evidence of \4scous flow. Gas inclusions 

 are abundant in the glass. The remainder of the material is made 

 up of scattered grains of plagioclase, quartz, hornblende, pyroxene, 

 relatively abundant bio tite, zircon, epidote, apatite, spinel (or garnet), 

 and cryptocrystalline calcite. This material is essentially shattered 

 volcanic glass (volcanic ash) with which are mingled mineral frag- 

 ments, some of which are not of volcanic origin. This ash was tested 

 with silver nitrate solution, and only a slight trace of chlorine obtained. 



The powder of this specimen, heated between 720° and 727° C. for 

 45 minutes, became flesh-colored, but otherwise remained loose and 

 noncoherent; heated to 1,100° for one-half hour, it became agglomer- 

 ated and shrunk to a hard, compact mass, but was not fused. Held 

 at 1,200° for 3 hours and then at 1,150° for 2 hours, it fused to a pale- 

 gray glass, which contained raicroscopic fragments of plagioclase and 

 particles of iron oxide. Gas bubbles were relatively common, but no 

 secondary microlites were observed. The refractive index of the 

 glass was fairly constant and averaged about 1.485. 



SPECIMENS FROM ALVEAR 



No. 263715. Specimen label. ^^ Locality: Alvear, on the Parana. 

 Material: Loess from the deposit in the ravine, selected hy Santiago Roth 

 for comparison with that from the Middle Pampean at a higher level. 

 This material appears to he a secondary deposit derived from, and 

 younger than, the Middle Pampean, hut Roth regards it as underlying 

 and older. B. W. 26 June, 1910." 



A, pale-brown, porous aphanitic earth, which consists largely of 

 plagioclase, quartz, and glass, with considerable argillaceous material. 

 Minor components are pyroxene, hornblende, biotite, and magnetite. 

 Most of the silicate fragments show some decomposition. The min- 

 eral grains average about 0.1 mm. in diameter and are usually sharp 

 and angular. 



This earth was mixed with bituminous coal and heated to 1,300° 

 for 30 minutes. It was then reheated at 1,300° for 2 hours and held 

 at 1 ,100° for 17 hours. The resulting gray glass contained fragments 

 of the original minerals and flakes and needles of hematite and acicular 

 microlites of a substance of medium birefringence and refractive 

 index considerably higher than 1,52. The minute crj^stals showed 

 parallel extinction, with the least elliptic axis parallel to the direc- 

 tion of elongation, but they proved too fine for satisfactory determi- 

 nation. The refractive index of the glass ranged from 1.505 to 

 1.525. 



