4 ^ 
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 
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 
consisting 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 melaphyres. The former 
are common rocks widely distributed in the form of dykes and in- 
trusive sheets. They are popularly known as trap rocks. Their 
composition 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, including 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 
in this order: Sandstones, conglomerates, breccias, quartzites, 
shales, clays, tufas or tuffs, coquina, chalk and limestones. 
Cases 8, 9 and 10. — Metamorphic rocks. 
These are divided into the stratified or bedded, and foliated 
or schistose. 
The first class includes crystalline limestones, marbles and 
dolomites .’They are made up chiefly of the mineral calcite, and are 
formed from the remains of mollusks, corals and other animals. 
