6o 
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. 
Kemaiiider 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, serpentme 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 
in this order: sandstones^ conglomerates^ breccias^ quartzites, 
shales, 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 crystalline dhnestones, marbles and 
doloinites. They are made up chiefly of the mineral calcite, and 
are formed from remains of mollusks, corals and other animals. 
These produced limestone first and this was changed by the action 
of heat to the crystalline condition, In some cases the original fos- 
sils remain intact, as is illustrated in many of the polished slabs. 
Upper part of Case 9.— Specimens illustrating rock 
texture, veins, rock folding. A series of wooden models illustrates 
structures produced by faulting. 
Cower part of Case 9 and. Case 10.— Following the 
marbles AVQ placed the crystalline schists, which are rocks of var- 
iable composition, but characterized by a pronounced schistose 
structure, especially where mica is the prevailing constituent. 
Here are included argillite, clay-slate, eclogite^ quartzite, phyllite^ 
paragonite schist, chlorite schist, mica schist, and others. 
Last in the series appear the gneisses, a class of rocks essen- 
tially like the granites in composition, but differing from them in 
structure, in that the constituents are arranged in approximately 
parallel bands or layers. These are the oldest of crystalline rocks, 
and are considered by many to represent portions of the primeval 
crust. Others, however, regard granites as the last term in the 
metamorphism of such rocks, and for that reason the gneisses 
have been placed in juxtaposition to them. Varieties of gneiss, 
based upon the prevailing mineral, whether biotite, muscovite, 
hornblende , or others, are included here. 
