
48 STRUCTURAL AND FIELD GEOLOGY 
amphibole, pyroxene, black garnet, sodalite, haiiyne, or nosean, etc. 
Leucite-phonolite is a phonolite in which leucite takes the place of 
nepheline ; when hatiyne occurs instead of nepheline we have Haziyne- 
phonolite. When leucite largely takes the place of sanidine the rock is 
known as Leucztophyre. In the vacuoles, fissures, etc., of all phonolites, 
zeolites and calcite are of common occurrence. 
The syenites play much the same part as the granites— 
occurring as more or less deep-seated plutonic rocks—while 
orthoclase-porphyry and minette are also intrusive, but appear 
chiefly in the form of sills and dykes. The trachytes may 
be looked upon as the effusive or volcanic representatives of 
ordinary syenites ; while the phonolites, in like manner, may 
be the effusive equivalents of the plutonic eleeolite-syenites. 
2. ROCKS WITH DOMINANT SODA-LIME FELSPAR 
This group includes some of the so-called “intermediate ” 
types (diorites and andesites), and others which are on the 
whole more basic (gabbros, dolerites, and basalts). Like the 
rocks of the preceding division, they are holocrystalline, hemi- 
crystalline, and vitreous. 
Diorite is a holocrystalline aggregate of plagioclase and a 
ferromagnesian mineral which may be hornblende, biotite, 
augite, or enstatite. The rock varies in texture from granitoid 
to compact—the granitoid varieties being speckled green and 
white, while the compact kinds are often dark green. Acces- 
sory minerals are—apatite, magnetite, sphene, zircon, etc. 
The following varieties are recognised :— Quartz-diorite = quartz + 
plagioclase+hornblende or biotite, or both. [It may be noted that a 
little quartz may be present in any diorite.] 7/cca-diorite=plagioclase 
+ biotite, and Axgite-diorite = plagioclase + augite—in both these 
varieties hornblende is often present. Zomadzte (Plate XII. 2) is a quartz- 
mica-diorite, containing some orthoclase, and approaching hornblende- 
granite. Many diorites are conspicuously porphyritic. Corsz¢ée (Orbicular 
Diorite) is a rock in which the constituents have crystallised together so 
as to form spherical aggregates having a concentric radiate structure 
(Plate XIV.). Kersaniite is a dioritic mica-trap composed essentially of 
plagioclase and biotite. The diorites, although widely distributed, are 
not very abundant. They occur chiefly as intrusive masses or as dykes 
and veins. 
Andesite is a hemicrystalline rock, usually dark coloured 
grey to brown. It consists essentially of plagioclase with a 

