WEiGHT-FENNER] PETEOGEAPHIC STUDY 67 



On immersion in water this specimen disintegrates readily into a 

 lumpy mud. The water solution above was found to contain abun- 

 dant chloride (probably common salt). 



No. 263742. Specimen label. ^'Locality: Mar del Plata, Barrancas 

 del Norte. Material: ' Tosca,' from the 'Ensenadean' of AmegTiino." 



A light-gray-brown, stony material of fine, even grain. The 

 microscopic examination of the specimen revealed the presence of 

 very fine-grained calcite, in which are embedded many larger grains 

 of plagioclase, quartz, colorless glass, and a little pyroxene. Both 

 macroscopic and microscopic evidence indicates a concretionary 

 limestone or nodule in the loess formation. 



On immersion in water this specimen remains fairly intact. Tested 

 with silver nitrate solution it gives a strong cliloride reaction (prob- 

 ably common salt). 



No. 263740. Specimen label. " Laguna de los Padres, 10 miles 

 west of Mar del Plata. Material: Balced loess from hole about 12 

 inches deep in which there had been a large hot fire." 



A burnt-looking earth, light-brown to black in color, which crumbles 

 to a fine, soft powder. Under the microscope the most abundant 

 components were found to be plagioclase and glass, both partly 

 decomposed and stained with iron oxide. Hornblende, pyroxene, 

 zircon, apatite, epidote, and magnetite (often altered) were j)resent 

 in smaller quantities. Argillaceous material is widely disseminated 

 through the rock. The color of the black portion appears to be due 

 to carbonaceous material, and merely the blackening from the fire. 

 There is no evidence of fusion. 



Immersed in water this specimen remains fairly intact and only 

 here and there crumbles down to mud. Its water solution contains 

 abundant chloride (probably sodium chloride). 



No. 263703. Specimen label. ^'Locality: Bajada Martinez de Hoz- 

 Barrancas de hs Lobos. South of Mar del Plata. Material: ' Tosca' 

 from lower part of the ' Chapadmalean' [^] formation of Ameghino." 



This large specimen is not homogeneous tlu-oughout but includes 

 two different types of material — a light-brown earth and a grayish- 

 brown, stony substance which is evidently concretionary in character. 

 The brown earth was found under the microscope to consist chiefly 

 of earthy argillaceous substance, plagioclase, and volcanic glass. 

 The argillaceous material was usually stained brown by iron oxide. 

 The plagioclase fragments were quite fresh and ranged in composition 

 from andesine to labradorite, the individual fragments often showing 

 zonal growth. Orthoclase and quartz were also observed and occa- 

 sionally grains of magnetite, pyroxene and hornblende. In general 

 aspect tliis earthy specimen is not unlike No. 263702 from Buenos 

 Aires. 



[' Written also Chapalmalean. j 



