236 Washington — Catalan Volcanoes and their Hocks. 



Pan. is transitional between this and the succeeding type, the 

 feldspar tables being extremely small and very sparingly 



present. 



Lirriburgose {Liniburgite\ San Roque type. 



Rocks of this type were but rarely met with, and they differ 

 from the most vitreous of those just described chiefly in the 

 absence of feldspar. While, therefore, they may be regarded 

 as probably but a variant of the other type, yet they may be 

 discussed separately on account of the mineralogical dissimi- 

 larity. 



Megascopic characters. — Contact, dark gray, aphanitic, 

 almost wholly aphyric, only a few very small nodules of brown- 

 ish augite being visible, though in certain lights the fresh 

 fracture shows an ill-defined glimmer, due to the presence of 

 scarcely visible, miuute prisms (of augite). 



Microscopic characters. — The rock is microporphyritic, 

 about 10 per cent of microphenocrysts of augite and -5 of 

 olivine being present. The former are anhedral to subhedral, 

 from 03 to l - mm . long, stout prismatic to fragmentary, and 

 of a pale brownish gray color : the latter euheclral to subhe- 

 dral, - 2 to 0*5 mra in diameter, colorless. Both carry inclu- 

 sions of small magnetite grains. The microgroundmass 

 consists of numerous, subhedral prismoids of pale brownish 

 augite, 0*1 to O03 mm long, and fewer magnetite anhedra, of 

 about the same size, but no olivine, embedded in a colorless, 

 isotropic base, which is evidently glass. JSfo flow texture is 

 evident, and the small augite prismoids are too stout and nearly 

 equant for the texture to be considered typically hyalopilitic. 



Mode. — As the type is highly vitreous, the mode is indeter- 

 minate, and the small size and crowded arrangement of the 

 groundmass augites renders any exact estimate of their amount 

 difficult. Consideration of the norm given below, and study 

 of the sections, however, indicates that the following figures 

 will express roughly the mode of the San Roque rock : 



Augite 35*0 



Olivine 5*0 



Magnetite - 10-0 



Glass 50-0 



100-0 



It may be said of this that the microphenocrysts of augite 

 constitute about 10 per cent and the small groundmass crystals 

 about 25, while olivine seems to be present only as micropheno- 

 crysts, of which certainly not more than 5 per cent are pres- 

 ent. On referring to the norm given later, it will be seen that, 



