41 
?rtx r OF 5.-Syenite-nephelinite series. 
First GROUP.-First row. Syenite, minette, etc. Holocrys- 
talhne rocks, having orthoclase and biotite as essential consthu- 
Second row. Trachytes. Tertiary eruptive rocks, charac- 
terized by the predominance of an alkaline feldspar, usually 
sanidine, and freedom from quartz. An iron-bearing mineral 
IS also usually present. mmcrai 
Second GRoup-First row. Nepheline or elaeolite syenites. 
Rocks composed of nepheline, orthoclase, and usually a pyrox- 
enic mineral and plagioclase feldspar. 
Second row. Phonolites, rocks consisting of an alkali 
feldspar, with minerals of the nepheline and leucite groups, and 
usually a monoclinic augite. 
Thii® GRovp.—Tephrites and basanites, rocks having neph- 
^me or leucite and lime-soda feldspar as essential constituents. 
They are usually porphyntic in structure, with a more or less 
amorphous ground mass. 
Fourth GjovF.—Kersantite, leucite basalt, leucitite, nephe- 
line basalt and nephehnite. Rocks containing leucite or nephe- 
a'ugite” ^ feldspar, and these usually associated with 
CASE 5 AND PART OF CASE 6.-First Group. Diorite 
and varieties-holocrystMmt rocks, having plagioclase feldspar 
and hornblende or black mica as essential constituents. 
Second row. Andesites and dacites, amorphous or porphy- 
ntic rocks composed of soda-lime feldspar, black mica, horn- 
blende, and in the case of the dacites. quartz. 
Third row. Porphyrites of various kinds. 
Second Group.— First row. Gabbros and norites. Rocks 
consisting of a basic soda-lime feldspar, with diallage or other 
pyroxene. 
Second row. Diabases, rocks having plagioclase feldspar 
3.na augite as essential constituents. 
Third row. Basalts, dolerites and melaphyres. The former 
■are common rocks widely distributed in the form of dykes and 
intrusive sheets. They are popularly known as trap rocks. 
Iheir composition is like that of the preceding. 
Third Group.— First row. Pyroxene rocks, diallagite. etc. 
Basic rocks, composed largely of pyroxene. 
