234 Washington — Catalan Volcanoes and their Rooks. 



undoubtedly nephelite. In the more scoriaceous material the 

 base is entirely vitreous, and is apt to be much obscured by 

 the abundant black dust spoken of above. 



The textures offer nothing of special interest, being com- 

 mon to many such basaltic rocks. The feldspars are not 

 sufficiently large, or numerous enough to render the rock 

 ophitic, and in the more compact forms the texture may best 

 be designated as hyalopilitic, while in the more glassy ones 

 it is simply vitrophyric. 



Mode.— Owing to the very small size of the groundmass 

 constituents and the consequent extensive overlapping, as well 

 as the presence of glass in many cases, no satisfactory estimate 

 of the mode by Rosiwal's method was possible. However, by 

 making certain readjustments from the figures furnished b} r 

 the chemical analyses, on the basis of the relations between 

 norm and mode observed in the Castellfullit rock, the modes 

 of three of the more compact analyzed specimens were calcu- 

 lated to be approximately as follows : column I representing 

 that of the Llora specimen, II that of the rock from the "sum- 

 mit of Garrinada, and III that from Las Planas. 



I II III 



Labradorite, (AbjAnJ 35-0 35*0 38*0 



Nephelite 12*0 10-0 6"0 



Augite 25-0 30-0 28-0 



Olivine 15'0 8-0 13-0 



Ores 11-0 15-0 14-0 



Apatite.. 2-0 2-0 1-0 



100-0 100-0 100-0 



Chemical composition. — Analyses of five rocks of this type 

 will be found in columns II to VI of the table on page 239. 

 Of these, the first three represent the more compact forms, 

 II and IV being flows and III being a somewhat scoriaceous 

 lava block, while the last two (V and VI) are scoriaceous lavas 

 from the recent cones. As compared with the analysis of the 

 Castellfullit flow, they are distinctly lower in silica, but resem- 

 ble it in other respects, and each other in all, very closely. 

 The greatest variation is seen in the relative figures for the 

 iron oxides, where there seems to be evident an increase of 

 ferric oxide at the expense of ferrous in the more scoriaceous 

 lavas of the cones, which may reasonably be referred to the 

 difference in the conditions which obtained during the extru- 

 sion and solidification, the possibilities of the oxidation of 

 ferrous to ferric oxide being greater in a vesicular lava than 

 in a compact flow. The uniformly high figures for Ti0 2 , 

 which vary within very narrow limits, are also to be noted as 

 an important feature. 



