55 
Case 4 and part of Case 5.— First Group, diorite and 
vdTieties — holocrystalline rocks, having" plagioclase feldspar and 
hornblende or black mica as essential constituents. 
Second row, (uidesites 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 7iorites. Rocks 
consisting of a basic soda lime feldsp r, with diallage, or other 
pyroxene. 
Second row, diabases, rocks having plagioclase feldspar and 
augite as essential constituents. 
Third row, basalts, dolerites and 77 ielaphyre<s>. i he 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, y)yroxe7ie rocks, diallagite, etc. 
Basic rocks, composed largely of pyroxene. 
Second row, iieridotite and varieties, including Iherzolite, 
picrite, and duTiite. These are highly basic rocks, composed 
chiefly of olivine, but having chromite and other iron oxides usually 
present. 
Remainder of Case 5, Cases 6 and 7 .—Sedimentary 
rocks. Rocks formed as chemical precipitates are placed first. 
» Xhese include he77iatite, Ii77i07iite, calcareous tufa, oolitic piso- 
litic Imiestones , onyx, several polished slabs of which are shown, 
serpentine and its varieties, also illustrated by many polished 
slabs, talc or steatite including verd-antique 77iarble and ophite, 
gypsu 77 i, 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, bixccia, quartzite, shale, 
clays, tufas or tuffs, coquina, chalk and limestones. 
Cases 8, 9 and lO.— Metamorphic rocks. 
These are divided into the stratified or bedded, and foliated 
or schistose. 
The first class includes the crystalline limestones, inai'bles, 
and dolomites. These are made up chiefly of the mineral calcite, 
and are formed from remains of mollusks, corals, and other ani- 
