666 HISTORICAL GEOLOGY 



remains of 800 cave bears were found ; from one in Sicily 20 tons of 

 hippopotamus bones were taken. A cave in Pennsylvania (Port 

 Kennedy), 60 to 70 feet deep, has yielded 64 species of mammals, of 

 which 40 are extinct, among them being giant sloths, tapirs, mas- 

 todons, and saber-toothed tigers. In a California cave, horses, 

 camels, ground sloths, mastodons, and other extinct forms have been 

 identified. 



Caves were doubtless inhabited by the land animals of the Ter- 

 tiary and other periods, but as caves have a relatively short life, they 

 and their contents are rarely preserved in the older formations. 



(2) Marshy ground in the vicinity of springs has often preserved 

 many fossils, since at such places carnivores frequently kill their prey 

 when the latter are coming down to drink ; and in times of drought 

 the animals of the region congregate about the water holes, where 

 they often die in large numbers. Many also are doubtless mired 

 in wet seasons. One of the most famous of such deposits (Big Bone 

 Lick, Kentucky) has yielded 100 specimens of mastodon, 20 speci- 

 mens of elephant, as well as bisons, musk oxen, and other animals. 



(3) An asphalt deposit (Fig. 576) not far from Los Angeles, Califor- 

 nia is remarkable, not only because unusual, but also because of 

 the number of specimens preserved in it. In the early stages of 

 the accumulation of the asphalt, the gummy surface apparently 

 acted as a trap for unwary animals ; where there were pools of water, 

 aquatic birds of many kinds were entrapped in the soft tar about 

 their margins; while land birds and smaller mammals were en- 

 snared in attempting to reach the water. Sloths, mammoths, horses, 

 camels, saber-toothed tigers, together with many birds, among which 

 is a fossil peacock, are only a few of the numerous species already 

 identified. 



(4) Wind-blown sand and volcanic dust have covered and pre- 

 served skeletons which have since been uncovered and studied. 



Difficulty is experienced in determining to what portion of the 

 Pleistocene the deposits not found between sheets of drift belong, but 

 four " zones," or subdivisions, of which certain animals are character- 

 istic, have been recognized. 



Deposits on the Last Drift. — The peat bogs which rest upon the 

 drift of the last ice sheet (Wisconsin) have yielded a number of masto- 

 don and mammoth skeletons. One mastodon found at Newburg, 

 New York, had its legs bent under the body and the head thrown up, 

 evidently in the very position in which it was mired. The teeth were 



