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1. E^ levators 



2. Fossil Fishes 



FOURTH FLOOR 



Foreword on Fossil Vertebrates 



In the East Corridor, and the South Pavilion at the left, as well as in 

 the East Wing and Southeast Pavilion at the right, are displayed the fossil 

 mammals, reptiles, and fishes. 



In a general way, fossils are the petrified remains of plants or animals 

 that lived at some past period of the earth's history. In many instances 

 we have not the objects themselves, but only their casts or impressions in 

 the rocks. This is particularly the case with shells. Sometimes, as with 

 the bones of the great Irish elk, the objects have been buried in swamps or 

 bogs, and in a few rare instances, as with the mammoth and woolly 

 rhinoceros, entire animals have been preserved for thousands of \'ears 

 in ice or frozen mud. Fossils are found in localities where the dead 

 animals or plants have gradually been buried under layers of sediment 

 to such a depth that they come in contact with the mineral waters of the 

 earth and finally become petrified. Later through subsequent upheaval 

 and erosion they are again brought to or near the surface of the earth. 

 Petrifaction is the slow replacement of animal or vegetable material 

 by such minerals as carbonate of lime or silica. The process is very 

 slow and for this reason flesh is never petrified. Fossil beds are found 

 in every continent. In our own country, Texas, Montana, Wyoming, 

 and the Bad Lands of South Dakota are famous for their large fossil 

 beds, and many of the finest and rarest fossils in the Museum were 

 obtained in these localities. 



As it takes thousands of years for the various layers of earth to 

 accumulate over the bones, and for the latter to become petrified, the 

 study of fossils and the strata in which they are found is an important 

 aid in determining the age of the earth and the succession of hfe thereon. 



