THE AMERICAN MUSEUM QF NATURAL HISTORY 



hemispherical forms which illustrate the six stages in the 

 geographical development of the North American conti- 

 nent. The stages represented are the Upper Cambrian, 

 Middle Devonian, Upper Triassic, Lower Cretaceous, Up- 

 per Cretaceous, Upper Oligocene. On each model the pres- 

 ent outline of the North American continent has been 

 superimposed upon that of the ancient lands and seas. 

 They differ widely from the modern outlines in all instances 

 except the Oligocene, which is more nearly like the present 

 map. These models represent the first attempt at restoring 

 the relief of the ancient lands on a curved surface. 



The desk cases down the center of the hall contain the 

 types and figured specimens used by James Hall, R. P. 

 Whitfield and others in the original description and naming 

 of species. Most of the American specimens are from New 

 York State, although there are many from the Middle West- 

 ern States. The type series, as it is designated, is arranged 

 biologically under each period, beginning with the oldest 

 fossiliferous period, the Cambrian, at the entrance. Geolo- 

 gists regard this series, with its 10,000 specimens, as the 

 largest and most valuable collection of fossil invertebrate 

 types in America. Toward the far end is a beautiful col- 

 lection of fossil sponges from northwestern Germany. 



The specimens in the upright cases, at the east or right- 

 hand side, are being arranged to illustrate the development 

 and relationship of the more common species of plants and 

 animals of past geologic times. In the first case are strik- 

 ing examples of carbonization and silicification of woody 



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