57 
Case 4 and part of Case 5.— 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 daciteSy quartz. 
Third row. Porphyrites of various kinds. 
Second Group. — First row, gabbros and 7 iorites. 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 77ielaphyre^. 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 dmiite. These are highly basic rocks, composed 
chiefly of olivine, with chromite and other iron oxides usually 
present. 
Kemaincler of Case 5, Cases 6 and 7.— Sedimentary 
rocks. Rocks formed as chemical precipitates are placed first. 
These include he77iatite, limonite, calcareous tufa, oolitic and piso- 
litic limestones, onyx, several polished slabs of which are shown, 
serpentine and its varieties, also illustrated by many polished 
slabs, 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: sandstone, conglomerate, breccia, quartzite, shale, 
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 the crystalline limestones, marbles, 
and dolomites. These are made up chiefly of the mineral calcite, 
and are formed from remains of mollusks, corals, and other ani- 
