4 ^ 
Case 170. — A series of models of gold nuggets of remarkable 
size. 
Cases 18 and 19, — Crystals of fluorite and quartz of except- 
ional size and beauty, from various localities. 
Cases 20, 21 and 22. — Gems and ornamental stones. Here 
are shown minerals used as sources of gems and ornaments and 
a series of imitation gems tor comparison. A more extensive 
collection may be seen in Hall 32. 
Case 23. — Slab of lapis lazuli from Peru, probably the largest 
single block ever quarried. 
Case 24, — Group of amethyst crystals from Thunder Bay, 
Lake Superior. 
HALL 65. 
STRUCTURAL AND DYNAMICAL GEOLOGY, 
The specimens here shown (together with these in Hall 66), 
illustrate the materials of the earth’s crust and the processes of 
change which they undergo. They also illustrate many striking 
phenomena met with in the study of the earth’s crust which are 
sometimes grouped under the title of Phenomenal Geography. 
Case 1, — Results of the action of chemical forces. Dendrites 
— arborescent impressions on rocks of all kinds, which have often 
the beauty of a drawing. They are produced by the deposition of 
oxides of iron or manganese from waters which have permeated the 
strata. The aborescent forms are due to incipient crystalization 
similar to that which takes place when frost is deposited upon a 
window pane. Specimens illustrating metamorphism, which may 
be produced by pressure, as where chalk is changed to limestone, 
or by chemical changes, as where pyroxene alters to serpentine. 
Cementation, illustrated by specimens of coquina of various types, 
of trass, and of conglomerates varying in degree of consolidation. 
Cave products, including stalactites and stalagmites from the 
Mammoth, Luray, Wyandotte and other caves, together wdth 
g3q)sum, epsom salts and other interesting cave products. Stal- 
actites of sulphur, galena, barite and other minerals show that the 
formation of these objects is not confined to limestone regions. 
