22S Washington — Catalan Volcanoes and their Rod's. 



while the two may be referred to two periods, yet that the 

 only essential difference lies in the fact that the eruptions 

 which produced the cones were the final, explosive effects of 

 the vnlcanicity, the commonly small size of these cones testi- 

 fying to the comparative feebleness of these last manifestations. 

 Such a formation of small cinder cones of the Puy type, 

 and comparatively free from lava flows, during the last, feeble 

 phases of vnlcanicity, is a not uncommon phenomenon*, as 

 exemplified by the volcanic regions of the Auvergne and the 

 Eifel. It is of especial interest to note, in this connection, 

 that very similar cinder cones, composed of basaltic material 

 closely allied to those of the Catalan volcanoes, marked the 

 close of volcanic action in Sardinia and on Pantelleria and 

 Linosa ; the rocks of which are held to be related petrologi- 

 cally to those of Catalonia, f as will be described in subsequent 

 papers. 



Petrography. 



In the field the rocks of the Catalan volcanoes would be 

 unhesitatingly considered basalts, which vary in texture from 

 compact forms, dark gray to almost black in color, to highly 

 vesicular, spongy scorise and lapilli, the color of these being- 

 black when fresh, but often yellow or red through surface 

 decomposition. The more compact forms frequently show 

 phenocrysts of olivine and augite, both minerals being usually 

 visible in the same specimen ; while phenocrysts of feldspar 

 are extremely rare. In some flows, most notably that of the 

 Bafla de Bosch, in the bed of the Llemana near Llora, the lava 

 contains rounded nodules, varying in size from a few centime- 

 ters to a decimeter or more, which are made up of small grains 

 of greenish yellow olivine, with a few grains of magnetite. 



Examined microscopically, it is seen that augite in large 

 amount, and less quantities of olivine and of magnetite, are 

 present in all these rocks, while hornblende and biotite are 

 entirely wanting. With these there frequently occurs much 

 plagioclase feldspar, usually a labradorite, orthoclase not hav- 

 ing been definitely recognized. In a few of the specimens 

 this plagioclase is the only salic mineral present, so that these 

 are true feldspar-basalts, according to current nomenclature. 

 In other cases a considerable amount of nephelite, or of glass 

 with probably a nephelitic composition, is present with the feld- 

 spar, giving rise to nephelite-basanites ; while, again, neither 

 feldspar nor nephelite is present, a glass base replacing them, 

 so that the rock may be called a limburgite. From the de- 



* Sir A. Geikie, Textbook of Geology, 1903, vol. ii, p. 764. 



fCf. H. S. Washington, Quart. Jour. Geol. Soc, vol. lxiii, p. 69, 1907. 



