68 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



The indurated part of the specimen consists largely of fine, almost 

 aphanitic calcite. Occasionally coarser-grained patches of the 

 calcite occur, especially near and in the druses wliich are not uncom- 

 mon in the rock. Accessory components are plagioclase, quartz, 

 magnetite, and some hornblende. Tliis part of the material is 

 evidently concretionary limestone and similar in formation to the 

 Loess-kindel of Germany. 



The earthy part of this specimen disintegrates to a fine mud in 

 water; the calcareous part remains practically unchanged. A strong 

 chlorine reaction was obtained with silver nitrate from the water 

 solution which contained the earth. 



The concretionary calcite and the earthy portions of this specimen 

 were mixed together in about equal parts and heated to 1,050°; 

 brick-red, indurated material resulted but no melting. On another 

 charge, held at 1,200° for 30 minutes, incipient fusion was observed; 

 heated to 1,300° for 2 hours the powder melted down to a vesicular 

 glass, which was reheated for one-half hour at 1,300° and then cooled 

 to 1,100° and held at about that temperature for 16 hours (over 

 night). During this last period the temperature may have varied 

 30° or 40°. The product thus obtained was pale-brown, compact, and 

 stony in appearance. Under the microscope, the original mineral 

 fragments were found to have disappeared and the glass to have 

 recrystallized in large part. In the crystalline aggregate sections of 

 a colorless substance of medium birefringence, maximum refractive 

 index about 1.655, parallel extinction on square sections, apparently 

 uniaxial and optically negative, predominate and are probably 

 gehlenite. Minute specks of a higher-refracting, weakly birefracting 

 substance occur in the gehlenite sections but were too fine for satisfac- 

 tory determination. Low-refracting isotropic glass particles were 

 not uncommon. None of these crystallized substances were found 

 in the scoriae. 



No. 263712. Specimen label. ^^ Locality: Bajada Martinez de 

 Hoz-Barrancas de los Lohos. South of Mar del Plata. Material: 

 Loess of the ' Chapadmalean ' formation of Ameghino from the lowest 

 part of the exposure near high-tide level." 



A fine-grained, gray-brown earth, similar in appearance to specimen 

 263711, from the north of Mar del Plata. The mineral components 

 observed under the microscope are plagioclase, quartz, sanidine, 

 hornblende, biotite, zircon and magnetite. Volcanic glass and 

 argillaceous subtance are also present, the glass being relatively 

 less abundant than in many of the preceding specimens. The plagio- 

 clase is relatively abundant and appears in broken, twinned grains 

 averaging about 0.1 mm. in diameter; zonal growth is characteristic 

 of many of its fragments. In general type and composition this 

 earth is similar to the earths described above. Characteristic for the 



