WRIGHT-FENNER] PETEOGRAPHIC STUDY 69 



entire group is the abundance of siliceous volcanic glass and minerals 

 derived from igneous rocks. This earth disintegrates readily in water 

 to a fine mud. The water solution above it contains abundant 

 chloride (probably sodium chloride). 



Part of this specimen was powdered, mixed with bituminous coal 

 and heated to 1,300° for 30 minutes; a fused product was obtained. 

 After heatmg at 1,300° for 2 hours it was held at 1,100° overnight 

 (17 hours). A dark, glassy mass resulted, which contained remnants 

 of the original fragments of quartz and plagioclase set in a gla§s 

 matrix out of wliich hematite crystals in separate individuals and 

 stellate groups had formed in abundance; more rarely minute 

 acicular crystals, either isolated or in radial clusters, occurred 

 (probably pyroxene). Their optical properties, so far as deter- 

 mined, were: Refractive index high; birefringence medium to fairly 

 strong, extinction angle often large, with elliptical axis c nearest the 

 axis of elongation. The refractive index of the glass ranged from 

 about 1.510 to 1.525. 



SPECIMENS FROM MIRAMAR AND VICINITY 



No. 263701. Specimen label. '^Locality: Miramar. Coast for a 

 mile north. Material: Portion of ' Ensenadean' (AmegJiino) , represent- 

 ing the deposit above the intraformational unconformity." 



A grayish-brown, distinctly conglomeratic rock in which hardened 

 nodules, ranging up to 3 cm. in diameter, but generally less than 

 1 cm., are included in a fine softer matrix. Scattered through the 

 matrix are, furthermore, hard, brown, cherty grains, round, and 

 from a half to 1 cm. in diameter; microscopically these grains consist 

 in large part of quartz and chalcedony more or less filled with fine 

 particles of iron ore. The pale-gray nodules on the other hand 

 consist essentially of calcite in minute grains and clusters, associated 

 with which are a few larger grains of plagioclase (mostly albite and 

 oligoclase with occasional grains of labradorite), quartz, glass, 

 pyroxene, hornblende, and magnetite. The subangular appearance 

 of these nodules indicates that they were not formed in place but 

 were derived from rocks not far distant. The rounded and polished 

 chert grains, on the other hand, have evidently been transported 

 long distances. The matrix contains chiefly plagioclase, glass, and 

 argillaceous material. Minor components are quartz, pyroxene, 

 hornblende, biotite, magnetite, and zircon. This earth falls into 

 pieces when immersed in water; the soft material crumbles into mud 

 and the nodules remain intact. When tested with silver nitrate this 

 earth gave a strong cliloride reaction. 



No- 263710. Specimen label. "Locality: Miramar. Exposed 

 ' Ensenadean, ' ^ mile north. Material: Ferruginous segregation regarded 

 by both Ameghinos as ' Tierra Cocida.'" 



