WRIGHT-FENNBR] PETEOGKAPHIC STUDY 61 



the large amount of salic components and tlie abundance of free 

 corundum in the norm, vrhich is probably due to the argillaceous 

 material of the loess. If the rock were an eruptive rock its analysis 

 would be classified along -with those of certain granites and rhyolites, 

 which in the quantitative system are included in the subrang Teha- 

 mose of the persalane class. 



No. 263718. Specimen label. ^'Locality: Alvear on the Parana. 

 Material: Brick from the tower near the mass of burnt clay." 



A brick of ordinary red color and usual appearance. Under the 

 microscope angular fragments of quartz, plagioclase, and colorless 

 glass are seen to be embedded in a microcrystalline, reddish matrix 

 which is evidently argillaceous. The deep-red color is probably due 

 to the presence of hematite which has resulted from the dehydration 

 and breaking down of the limonitic material in the yello^\dsh and 

 brownish matrix of the original earths. The hematite is so fine, 

 however, that the microscope is of little assistance in the direct 

 determination, and the character of the microscopic red dust is 

 inferred rather than definitely determined. The thermal experiments 

 on the earths of this collection prove that many of them are suitable 

 for brickmaking. In the present specimen there is no trace of fusion. 

 When immersed in water this material remains intact. No trace of 

 chloride was obtained with silver nitrate solution. 



No. 263729. Specimen label. ^'Locality: Alvear on the Parana. 

 Material: Burnt clay from the remains of the lower 'part of the mass or 

 fogon originally discovered hy Roth. B. W. 26 June, 1910." 



A brick-red, terra-cotta-like material considerably indurated and 

 of fine, even grain. Under the microscope small angular fragments of 

 plagioclase, quartz, and glass were observed embedded in a fine 

 reddish matrix, evidently argillaceous in character. In comparison 

 with the earth (specimen 263717) the present material is similar in 

 composition and general texture except that the individual mineral 

 grains are possibly slightly smaller in average size. Both specimen 

 263717 and specimen 263729 exhibit cavities coated with chalcedony 

 and are intersected by films and threads of manganese oxide. 



This specimen remains intact when immersed in water and does not 

 crumble. When treated with silver nitrate only the slightest trace 

 of cliloride was obtained. In this respect the present specimen 

 resembles the two preceding specimens. 



This specimen was heated first to 1,300° for 30 minutes and then 

 held at 1,100° for 16 hours. The resulting melt was dark-purple in 

 color and consisted chiefly of glass in which occasional remnants of 

 the original mineral fragments were embedded and also numerous 

 microlites of hematite and rarely a minute, lath-shaped crystal, which 

 was too fine for satisfactory determination. The major part of the 



