WRIGHT-FENNER] PETROGRAPHIC STUDY 63 



material in 263718 and 263729; (2) the close similarity between the 

 chemical analyses of 263717 and 263729; (3) the presence of chalce- 

 dony lining the cavities in 263717 and 263729; (4) the close resem- 

 blance in texture and color between fragments of 263717, baked at 

 870° over night, and fragments of 263718 and 263729. The frag- 

 ments of 263718 were baked in general slightly harder than those of 

 263729. (5) the identity of the glassy products obtained by fusing 

 263717 and 263718. (6) The absence of sodium chloride from all 

 three specimens. These facts prove with reasonable certainty that 

 the earth, the tierra cocida, and the bricks, just described from Alvear, 

 are of the same material, and that the last two have been heated under 

 the same general conditions. The tierra cocida in this case is prob- 

 ably the fragmental baked material from the old brick kiln in which 

 the bricks were made. 



No. 263738. Specimen label. ''Locality: Saladillo near Rosario. 

 Material: Burnt clay, calcareous concretions, and animal hones from 

 the conglomeratic layer in the 'Middle Pampean' of Roth. B. W. 

 25 June, 1910." 



As indicated in the specimen label, a number of different rock types 

 have been included in this lot: (a) Soft-brown loess of the usual 

 characteristics and composition (chiefly fragments of quartz, plagio- 

 clase, hornblende, magnetite, and argillaceous material); (b) pieces 

 of baked loess ranging in color from brick-red to brown and often 

 containing dark linings of probable manganese oxide; (c) nodules of 

 finely crystalline calcite; (d) black nodules rich in phosphate and 

 evidently associated with (e) bones which have been highly altered 

 and contain fine, microcrystalline calcite and black phosphatic 

 material and a pale-yellow to white, microcrystalline substance of 

 weak to medium bu'eiringence and refractive index about 1 .60. This 

 substance occurs in so intricately intergrown and overlapping 

 aggregates that further optical properties could not be determined 

 \vith certainty. (/) Rounded pebbles of a substance which agreed 

 in its properties with the white substance just described were also 

 observed and tested chemically. The pebble tested was examined 

 under the microscope and found to be practically homogeneous. 

 Heated in a closed tube a small amount of water was obtained. The 

 substance is completely soluble in dilute hydrochloric and also nitric 

 acid with strong effervescence of carbonic-acid gas. Phosphoric acid 

 was found to be one of the principal constituents; also calcium. The 

 mineral is evidently a hydrated calcium carbonate-phosphate. The 

 only mineral listed in Dana's Mineralogy of this nature is dahllite, 

 whose optical properties, so far as determined, agree approximately 

 with those recorded above. The density of this substance, however, is 

 about 2.53, which is quite dift"erent from that given for dahllite 

 (3.053). Unfortunately not enough of this material is available for 



