57 
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. — Kersantite , leucite basalt , leucitite , nephe- 
line basalt , and nephelinite . 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, andesites 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 ?nelaphyres. 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, pyroxene rocks , diallagite , etc. 
Basic rocks, composed largely of pyroxene. 
Second row, peridotite and varieties, including Iherzolite , 
picrite and dunite. These are highly basic rocks, composed chiefly 
of olivine, but having chromite and other iron oxides usually 
present. 
Remainder of Case 6 and Case 7.— Aqueous rocks. 
Rocks formed as chemical precipitates are placed first. These 
include hematite , limonite , calcareous tufa , oolitic and pisolitic 
limestones , onyx , serpentine and its varieties, talc or steatite , in- 
cluding verd-antique marble and ophite , gypsum, alabaster , etc. 
Then follow rocks formed as sedimentary deposits, and frag- 
mental in structure. The principal varieties of these are arranged 
