Parr Il. § vi] CRYSTALLINE ROCKS—MASSIVE. 131 
_ proximately equal size ; (b) pegmatoid, where there has been a simul- 
taneous crystallization and regular arrangement of two constituents ; 
(c) ophitic, in which the felspars are ranged parallel to one of their 
crystalline faces, forming a kind of transition into microlithic rocks. 
2. Trachytoid, distinguished by a more marked contrast between 
the crystais of the first and second consolidation, the usual presence 
of an amorphous magma, and the fluxion structure. ‘Three types are 
named, (a) petrosiliceous, with trains and spherulites of a finely clouded 
~ substance characteristic of the more acid rocks; (b) mecrolithic, cha- 
_ racterised by the abundance of microliths of felspars and other 
Ininerals; (c) vitreous, derived from the two foregoing types by the 
predominance of the amorphous paste.’ 
(1.) Felspar-bearing Series. 
a. Orthoclase Rocks. 
a. Quartziferous. 
In this family the silicic acid has been in such excess as to 
separate out abundantly in the form of free quartz. Sometimes, 
as in granite, it has not assumed a definitely crystallized form, but 
is moulded round the other crystals as a later stage of consolidation. 
In other rocks (quartz-porphyry, &c.) it occurs as a product of earlier 
consolidation. It often assumes perfect crystallographic contours, 
occurring eyen in double pyramids. The texture of the rocks is 
(1) erystalline-granular (granitoid) as typically developed in granite; 
(2) porphyritic (trachytoid), as in quartz-porphyry or felsite; (8) 
vitreous, as in pitchstone. 
Granite.2—A thoroughly crystalline-granular admixture of fel- 
spar, mica, and quartz in particles of tolerably uniform size. The 
felspar is chiefly white or pink orthoclase, but triclinic felspars (oligo- 
clase and albite) may often be observed in smaller quantity, fre- 
quently distinguishable by their fine striation and more waxy lustre. 
The mica may be either the potash or muscovite variety, usually of a 
white silvery aspect; or may belong to biotite (magnesian mica) or 
lepidomelane, when it is commonly dark brown or black. Dr. Heddle 
finds the common mica of the granites in the Scottish Highlands to be 
a new variety, which he has called haughtonite. The quartz may be 
observed to forma kind of paste or magma wrapping round the other 
ingredients. Only in cavities of the granite do the component minerals 
occur in independent well-formed crystals, and there too the accessory 
minerals (beryl, topaz, tourmaline, &c.) are chiefly found. 
From a microscopic examination of granite it was formerly in- 
1 Op. cit. p. 150. 
2 On the structure of granite see the manualsof Zirkel and Rosenbusch and the 
memoirs there cited; also Zirkel’s Microscop. Petrography, 1876, p. 39; Phillips, 
Q. J. Geol. Soc. xxxi. p. 330; xxxvi. p.1. J. C. Ward, op. cit. p. 569, and xxxii. p. 1. 
King’s Systematic Geology (vol. i. of Explor. 40th Parallel), p.111, et seg. Michel-Lévy, 
Bull. Soc, Géol. France, drd ser. iii. p, 199. 
, K 2 
