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COl L ECTION.i| I I II 



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FOS5I L MAMMALS 



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1. Elevators. 



2. Fossil Fishes. 



FOURTH FLOOR I 

 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 years 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 accumu- 

 late 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 de- 

 termining the age of the earth and the succession of life thereon. Many 

 of the skeletons exhibited in these halls are of animals which hved 

 from 30,000 to 20,000,000 years ago. To prepare a specimen for 



87 



