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Floor-case No. 9 is devoted to plants of the Upper 
Cretaceous (Laramie Group), and completes the vegetation 
of Mesozoic time. 
Floor-cases Nos. 10 to 12 and wall-case No. 5 contain 
plant remains of Neozoic time. Those of the early Ter- 
tiary Period (Eocene) are displayed in floor-case No. Io. 
Those of the later Tertiary (Miocene) and Quaternary 
Periods in floor-cases Nos. 11 and 12. The specimens in 
the latter case complete the sequence of plant life on the 
earth and bring it up to modern times. A number of 
specimens at one end of the case show the methods of 
preservation by petrifaction, incrustation and carboniza- 
tion, and on the upper shelf is a series of specimens from 
Oia ena) and more recent swamp deposits which show 
how the conversion of living plants into fossils, a process 
now going on, has its beginning. 
The specimens in wall-case No. 5 further illustrate the 
characteristics of the plants of the late geological periods 
and the methods by which the various plant structures 
have been preserved. A number of specimens of silicified 
woods show the method of preservation by what is known 
as petrifaction, or conversion into stone, in which the 
woody structure is replaced by mineral matter. Other 
specimens show preservation by incrustation, in which 
mosses and the stems of reeds are coated or incrusted by 
minetal matter deposited from springs; while on the upper 
shelf on the top of the case are logs and stumps from old 
swamps and interglacial deposits, in which the wood has 
been partially carbonized, or converted into lignite, by 
the slow process of natural distillation. This process 
represents the beginning of the conversion of vegetable 
tissue into coal. 
LECTURES 
Other features of the museum building include the large 
public lecture hall, with a seating capacity of over seven 
hundred, which occupies the western end of the basement. 
It is equipped with an electric projection-lantern, and free 
