42 
Second row. Peridotite and varieties, including IhergoHte,. 
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 verdantique marble and ophite, gypsum, ala- 
baster, etc. 
Then follow rocks formed as sedimentary deposits, and 
fragmental in structure. The principal varieties of these are 
arranged in this order; Sandstones, conglomerates, breccias, 
quartzites, shales, clays, tufas or tuffs, coquina, chalk and lime- 
jfoHW^SEs 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. These produced limestone first and this was changed 
. by the action of heat to the crystalline condition. In some 
cases the original fossils 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 illus- 
trates s-tructures produced by faulting. 
LOWER PART OF CASE 9 AND CASE 10 .— Following 
the marbles are placed the crystalline schists, which are rocks 
of variable composition, but characterized by a pronounced 
schistose structure, especially where mica is the prevailing con- 
stituent. Here are included argillite, clay-slate, eclogite, quartz- 
ite, phyllite, paragonite schist, chlorite schist, mica schist, and 
others. _ , ^ i 
Last in the series appear the gneisses, a class^ of rocks es- 
sentially like the granites in composition, but differing^ from 
them in structure, in that the constituents are arranged in ap- 
proximately parallel bands or layers. These are the oldest of 
crystalline rocks, and are considered by many to represent por- 
