46 
It is interrupted in the numbering of the cases in order to give 
place to some collections illustrating rock regions and to the sye- 
nite-nephelinite series. 
Case 2. — Collection of rocks of the copper and iron bearing 
regions about Lake Superior. This was prepared with great care 
by Mr. Oscar Rohn, and illustrates many important types of rocks 
in a region of great economic interest. 
Rocks of Manhattan Island. These were obtained chiefly 
from excavations made in and about New York City. They are 
crystalline, metamorphic rocks, and illustrate well the great vari- 
ations possible in kinds of rock in a small region. 
Upper part of Case 2. — Lavas of the best known volcanoes, 
such as Vesuvius, Mauna Loa and the extinct volcanoes of Central 
France. 
Case 3. — Lavas and other volcanic products of the volcanoes 
of the Valley of Mexico. 
Rocks of the Green Mountain Range, as seen in passing east- 
ward from Pittsfleld, Mass. 
These include a variety of schists, limestones and other meta- 
morphic rocks ranging in geological time from the Archaean into 
the Devonian. They illustrate the different formations distin- 
guished by geologists in the region. 
Case 4 and part of 5. — Syenite-nep he Unite series. 
First Group. — First row. Syenite, minette, etc. Holocrys- 
talline rocks, having orthoclase and biotite as essential constitu- 
ents. 
Second row. Trachytes. Tertiary eruptive rocks, charac- 
terized by the predominance of an alkaline feldspar, usually sani- 
dine, and freedom from quartz. An iron-bearing mineral is also 
usually present. 
Second Group. — First row. Nepheline or elaeolite syenites. 
Rocks comprised of nepheline, orthoclase, and usually a pyroxenic 
mineral and plagioclase feldspar. 
Second row. Phonolites, rocks consisting of an alkaline feld- 
spar, with minerals of the nepheline and leucite groups, and 
usually a monoclinic augite. 
Third Group. — Tephrites and basanites, rocks having neph- 
eline or leucite and lime-soda feldspar as essential constituents. 
They are usually porphyritic in structure, with a more or less 
amorphous ground mass. 
