(52) 



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. 10. 

 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 

 Quaternary 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 

 mineral 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 



