98 BUKEAU OF AMERICAN ETHNOLOGY [bull. 52 



average refractive index about 1.61, are common and have evidently 

 resulted from the alteration of the original bone substance. In optical 

 properties this substance resembles that described under specimen 

 263738. Fine grains of an isotropic, low-refracting substance also 

 occur but are too fine for identification. 



No. 263749. Specimen label. " Weathered modern hone from playa 

 of 'fossil man,' near Laguna Malacara, north of Necochea." 



This bone contains abundant cryptocrystalline calcite which has 

 evidently replaced much of the original bone substance. The weakly 

 birefracting substance, noted above and probably phosphatic in 

 composition, is also present in considerable quantities. 



No. 263753. Specimen label. ^' Cow, very recent; exposed to ele- 

 ments; lower jaw. Playa Peralta, near Mar del Plata." 



In this specimen no calcite was observed. The material consists 

 chiefly of a cryptocrystalline, weakly birefracting, low-refracting sub- 

 stance which is probably slightly altered bone substance. Evidently 

 this bone has suffered but slight alteration. 



No. 263754. Specimen label. "Rib. Necochea 'fossil' man." 



Contains both cryptocrystalline calcite and the weakly birefracting 

 substance noted above. Has evidently been altered considerably. 



No. 263755. Specimen label. "La Tigra slcull." 



In powder form this bone closely resembles the foregoing. In both 

 specimens the calcite is evidently a replacement product. 



No. 263756. Specimen label. "Ovejero. ShillNo.l." 



Practically no calcite was observed in this specimen. The powder 

 consists largely of a fine cryptocrystalline, weakly birefracting, low- 

 refracting substance which is probably bone substance. The material 

 is evidently not highly altered. 



No. 263757. Specimen label. " Fontezuelas sTcull." 



Contains both cryptocrystalline calcite and the weakly birefracting 

 phosphatic material, besides a lower-refracting isotropic substance. 

 This bone has obviously suffered considerable change. 



No. 263758. Specimen label. "Homo pampseus. Necochea." 



Resembles 263755 closely and has evidently suffered the same kind 

 of change. 



No. 263761. Specimen label. "Sea lion; very recent. Punta 

 Mogote." 



But very little calcite was observed in this specimen and was then 

 associated with yellow, iron-stained argillaceous material. A weakly 

 birefracting substance not unlike that described in many of the 

 specimens above constitutes the major part of the powder. 



Carnegie Institution of Washington, 



Geophysical Laboratory, Washington, D. C. 



