C3 



L^A Th^ -HU] < ) 



o 



«f05ilL MAMMALS /■"-'.'' r m <7,A.>»TIUJ 



u » u : ,, k — o 



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. Sometimes, as wit h 

 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 and for so long a time that they finally became petrified. 

 Later through 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, which are carried in solution by the underground waters. 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, Mont ana . 

 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 w T hich they are found is an important 

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

 The skeletons exhibited in these halls are of animals which lived from 

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



99 



