59 
Case 4: and part of ^.—Sye 7 iiie-nephelinite series. 
First Group. — First row. Syenite, minette, etc. Holocry- 
stalline rocks, having orthoclase and biotite as essential constitu- 
ents. 
Second row. Trachytes. Tertiary eruptive rocks, characterized 
by the predominance of an alkaline feldspar, usually sanidine, 
and freedom from quartz. An iron-bearing mineral is also usually 
present. 
Second Group. — First row. Nepheline or elaeolite syenites. 
Rocks comprised of nepheline, orthoclase, and usually a pyroxenic 
mineral and plagioclase feldspar. 
Second row. Phonolites, rocks consisting of an alkaline feld- 
spar, with minerals of the nepheline and leucite groups, and 
usually a monoclinic augite. 
Third Group. — Tephrites and basanites, rocks having neph- 
eline or leucite and lime-soda feldspar as essential constituents. 
They are usually porphyritic in structure, with a more or less amor- 
phous ground mass. 
Fourth Group. — Kersa^itite, leucite basalt, leucitite, 7iephe- 
liHe basalt, and 7iephelinite. Rocks containing leucite or nephe- 
line in place of feldspar, and these usually associated with 
augite. 
Case 5 and part of Case 6.— First Group. Diorite and 
varieties — holocrystalline rocks, having plagioclase feldspar and 
hornblende or black mica as essential constituents. 
Second row, a7idesites and dacites, amorphous or porphyritic 
rocks composed of soda-lime feldspar, black mica, hornblende, 
and in the case of the dacites, quartz. 
Third row. Porphyrites of various kinds. 
Second Group. — First row, gabbros and norites. Rocks con- 
sisting of a basic soda-lime feldspar, with diallage or other 
pyroxene. 
Second row. Diabases, rocks having plagioclase feldspar and 
augite as essential constituents. 
Third row. Basalts, dolerites and 77ielaphyres. The former are 
common rocks widely distributed in the form of dikes and intrusive 
sheets. They are popularly known as trap rocks. Their compo- 
sition is like that of the preceding. 
Third Group. — First row, py7'oxefie rocks, diallagite, etc. 
Basic rocks, composed largely of pyroxene. 
