Classification of Massive Rocks. . 299 
z (c 3) tholeiite, in which the constituents of the ground mass 
occur in but a single generation, and the structure 
is hypocrystalline through the existence of a little 
glass, which is aggregated in small areas between 
the crystalline components (intersertal structure). 
(D) augite-vitrophyrite, consisting principally of a glassy 
ground mass in which are a few microlites of 
plagioclase, augite and magnetite. 
1, MELAPHYRES, consisting essentially of plagioclase, augite and 
olivine. As in the augite porphyrite proper, three 
types are distinguished :— 
(A) navite, an olivine-bearing rock corresponding in struc- 
ture to labrador-porphyrite. 
(B) olivine-weiselbergite, with the characteristics of weisel- 
ergite. 
(c) olivine-tholeiite, an olivine-bearing tholeiite. 
E. THE PICRITE PORPHYRITES. 
The picrite porphyrites correspond to the intrusive peridotites. 
They are composed of idiomorphic olivine and augite crystals in a 
ground mass, which consists principally of a glassy base, which by 
devitrification often becomes weakly doubly refracting. 
The picrite-porphyrites are limited in their distribution. They 
are characterized particularly by the lack of feldspar in porphy- 
ritic crystals. 
III. B. Tae Nrovoitcanic ErrustvE Rocks. 
The neovyoleanie rocks occur principally as lavas, on the surface 
of the earth, as intercalated layers between sedimentaries, as dykes, 
voleanic necks and bosses. They are characterized by the vitreous 
appearance of the feldspars. 
_ They are diyided according to their mineralogical composition 
into families corresponding to those of the intrusive and paleovol- 
canic classes : 
A. THE LIPARITES AND PANTELLERITES. 
The liparites and pantellerites are composed essentially of an 
alkaline feldspar and quartz in porphyritic crystals, together i 
ground mass which may be either holocrystalline or glassy. i 
They are separated according to the nature of their porphyritie 
feldspathic constituents into liparites and pantellerites. n 
