WRIGHT-FENNBR] PETEOGRAPHIC STUDY 71 



and refractive index noticeably greater tlian 1.53; the microlites 

 extinguished parallel with their elongation but were too fine for 

 identification. The refractive index of the glass ranged fr©m 1.51 to 

 1.53. Neither hematite nor magnetite was present except in. traces 

 around the microlites. To vary the conditions of heating a larger 

 quantity of the earth was taken (100 grams) and heated in a Fletcher 

 gas furnace at 1,1 00°- 1,200° for half an hour and then quickly 

 withdrawn and aUowed to cool m air. The product thus obtained 

 was higlily scoriaceous and resembled closely some of the natural 

 scorias. The glass which had been formed was streaky, and varied in 

 refractive index from about 1.515 to 1.540. Grams of the original 

 quartz and plagioclase, pyroxene, and magnetite fragments were 

 still visible. The coolmg of the magma was rapid and no new crystals 

 were formed as a result. A second charge consisting of lumps of the 

 earth was heated in a similar way in the gas furnace but at slightly 

 lower temperature. The lumps assumed a glassy surface and 

 although entirely melted were evidently so vjscous that little evidence 

 of flow was noticeable. On both these samples red hematite was 

 formed on the outer glassy surface but, in the mterior of the lumps, 

 the mass was gray-black in color and no new hematite was observed 

 with certauity. The origmal magnetite fragments were still visible. 

 New crystallization had evidently not taken place. In both cases 

 the glass was full of small bubbles and streaky, and variable m 

 composition and refractive index (1.515 to 1.54). (PL 7.) The 

 evidence from the different methods of heating adopted above 

 indicates that the character of the product is dependent somewhat 

 on the heat treatment it has undergone. 



No. 263725. Specimen label. '^Locality: Miramar. Material: 

 Disseminated scoria." 



A pale-brown earth of uneven grain in which are imbedded pieces 

 of a grayish-black, scoriaceous substance of variable size and ranging 

 from large lumps to small pellets. The vesicles of the scoria have 

 usually a glazed surface and are often filletl with the earth which 

 surrounds them. There is no evidence of a transition between the 

 scoria and the earth. Clingmg to the scoria and firmly wedged mto 

 some of the small cavities are rounded grains of quartz, calcite, 

 plagioclase (oligoclase, andesine, and labratlorite), pyroxene, garnet, 

 magnetite, and volcanic glass. These grains are noticeably coarser 

 than the earth which surrounds the scoria and have evidently been 

 blown or washed into their present position. The lai'ger pieces of 

 scoria often appear freslily broken, but at the contact of undisturbed 

 scoria and earth the surface of tlie scoria suggests an origmal smooth, 

 rounded surface similar to the surface of a volcanic bomb or scoria 

 rather than that of an originally angular fragment which has been 

 subsequently rounded by attrition during water transportation. 



