WRIGHT-FENNER] PETKOGRAPHIC STUDY 77 



microlites. The magnetite of the original scoria appears to have 

 been largely absorbed. The earthy material in the second crucible 

 also melted down to a thick viscous glass which did not flow rapidly 

 enough to take the shape of the crucible during the time of exposure. 

 In it the original mineral fragments are still visible. The glass 

 present was colorless, but was filled with fine, dust-like particles of 

 iron ore. Its refractive intlex was about 1 .51 , while that of the brown- 

 colored scoria glass ranged from about 1.515 to 1.54, 



No. 263719. Specimen label. '^Locality: Miramar: Material: 

 Washed-in hits of Tierra Cocida and Scoria." 



A pale-brown loess of the usual t3^pe containing fragments of scoria 

 and red indurated material. The vesicular cavities of these scoriae 

 often contain rounded grains of quartz, chert, magnetite, plagioclase, 

 and pyroxene; these grains are occasionally tightly wedged into the 

 small bubble cavities. The loess contains much argillaceous material 

 and minute fragments of quartz, microcline, plagioclase, magnetite, 

 pyroxene, and colorless glass. Small worm-like cavities are common 

 and are evidently due to former grass roots. The scoriae pebbles are 

 similar to specimen No. 263734 in appearance and composition. The 

 red earth contains much brick-red, argillaceous material and also 

 minute fragments of quartz, acid plagioclase (oligoclase), pyroxene, 

 hornblende, and colorless volcanic glass. This red earth resembles in 

 its properties that of specimen 263731. This specimen crumbles 

 slightly and softens when immersed in water. Tested with silver 

 nitrate it gives a strong chloride reaction (probably common salt 

 derived from sea water.) 



No. 263720. Specimen label. ''Locality: Barrancas 3 to 5 miles 

 north of Miramar. to 5 feet above the base, i. e.,from the lowest for- 

 TTMtion above the beach. Ameghino's Chapadmalean. Material: Scoria 

 and burnt earth." 



This specimen consists of a large fragment of scoria, similar in 

 appearance and properties to No. 263728, embedded in pale-brown 

 loess of the usual properties and closely allied to No. 263719 in texture 

 and composition. 



Nos. 263724, 263726, 263733, 263734, 263737. Specunen labels. 

 "Locality: Mira^nar. Material: Scorise and Tierra Cocida." 



These specimens are similar to the specimens noted above from 

 this locality. The scoriae are of the same general appearance and 

 composition and contain in a pale-brown, streaky glass irregular and 

 rounded fragments of quartz, plagioclase (andesine, labradorite), 

 pyroxene, and magnetite. (PI 7, a.) The glass base is full of fine 

 bubbles and is often streaky and variable in refractive index and 

 composition. In No. 263737, the vesicles are large and elongated. 

 In one part of this specimen elongated drops of the viscous scoria are 

 visible and testify to the flowing of the molten scoria. In all of these 



