METHODS — PAL^ONTOLOGICAL 39 



scanty information, or none at all, while in the case of others 

 the story is wonderfully full and detailed. The latter are, 

 very generally, the groups which were not only numerically 

 abundant at all stages of their history, but also had skeletons 

 that were strong enough to resist destruction ; while the 

 groups as to which there is little or no information are chiefly 

 of small and fragile animals, or such as were always rare. 

 For example, a great deal has been learned regarding the de- 

 velopment of horses and rhinoceroses in North America, but 

 the history of the tapirs is very unsatisfactorily known, be- 

 cause, while horses and rhinoceroses were common, tapirs 

 were solitary and rare. In Europe bats have been found in 

 the Eocene, Oligocene and Miocene, and there is no reason 

 to suppose that they were not equally ancient and equally 

 abundant in America ; but none have been found in the western 

 hemisphere in any formation older than the Pleistocene. All 

 things considered, the extraordinary fact is, not that so many 

 forms have irretrievably perished, but that so much has been 

 preserved, escaping all the chances of destruction. 



As to the degree of preservation in fossil mammals, we have 

 to do almost entirely with bones and teeth. With very rare 

 exceptions, and those all of late geological date, the viscera, 

 muscles, skin, hair, horns, hoofs and claws have been com- 

 pletely destroyed and have vanished without leaving a trace. 

 In northern Siberia the gravel soil is permanently frozen to 

 a depth of several hundred feet and contains the intact carcasses 

 of elephants and rhinoceroses of Pleistocene date and notably 

 different from any species of these animals now in existence. 

 Sometimes such a carcass is disinterred from a bluff by the 

 cutting action of a stream and is in a state of nearly complete 

 preservation, with hide, hair and flesh almost as in an animal 

 freshly killed. From these remains it has been learned that 

 the jMammoth was an elephant densely covered with hair and 

 wool, just as he was depicted in the carvings and cave-paintings 



t Extinct. 



