DEl’ARTMEXT OF GEOLOGY 
tions, clay stones, sand and limonite concretions make up the bulk 
of the collection. A related structure called orbicular, found in 
eruptive rocks, is illustrated by large slabs from California, North 
Carolina, and Sweden. A number of geodes are shown illus- 
trating the forms and size of these bodies. The next case is 
largely devoted to septaria formed from concretions by drying 
and shrinking and a subsequent filling of the cracks with some 
other substance. Several of these shown are of large size, one 
being nearly three feet in diameter. Polished sections are also 
shown. The next case illustrates cave formations and cave life. 
Stalactites and stalagmites and other cave formations chiefly 
from Indiana caves are mounted in natural positions so as to il- 
lustrate the formation and characters of typical limestone caves. 
The forms of life inhabiting such caves are also shown. The 
next case is devoted to specimens of individual stalactites and 
stalagmites of large size or perfection of form; it also contains 
a series of fulgurites, one of which is nine feet in length. On 
the floor of the hall is a collection of basalt columns from the 
Giant’s Causeway, Ireland, and the Rhine valley. These are 
grouped so as to illustrate the stair-like arrangement which often 
characterizes cliffs of basalt. There is also on the floor of the 
hall a case containing a large number of crystals of sele- 
nite from Wayne County, Utah. In this exhibit the crystals are 
arranged in the geode-like form in which they occur at the orig- 
inal locality. 
Hall 66. 
LITHOLOGY. 
The chief collections of this hall illustrate the varieties of 
rocks. About 2,000 specimens are shown, most of them being of 
the size 3x4x1 inch. The specimens are classified under the 
heads of eruptive, aqueous, and metamorphic rocks. 
Entering from Hall 65, in the first case at the left of the 
entrance are shown granite and its varieties, such as granitite, 
graphic-granite, etc. These are coarse-grained rocks having 
quartz, potash-feldspar, and one or more minerals of the mica, 
amphibole, or pyroxene groups as essential constituents. Then 
follow granite-porphyry, quartz-porphyry, vitrophyre, felsophyre, 
etc., which are like the preceding in composition, but rnore or 
