BONE-CAVES. 91 



researches discovered a cavern the stalagmitic floor of which was entire. On penetrating the sparry 

 crust he found the usual ossiferou.s bod, but pressing engagements compelled him to leave the deposit 

 unexplored. After an interval of some years, M. Clausen again visited the cavern, and found the 

 excavation he had made completely filled wp with stalagmite, the floor being as entire as on his first 

 entrance. On breaking through this newlj'-formed incrustation, it was found to be distinctly marked 

 with lines of dark-coloured sediment alternating with the crj'stalHne stalactite. Reasoning on the 

 probable cause of this appearance, M. Clausen sagaciously concluded that it arose from the alternation 

 of the wet and diy seasons. During the drought of summer the sand and dust of the p)arched land 

 were wafted into the caves and fissures, and this earthly layer was covered during the rainy season by 

 stalagmite, from the water that jjercolated through the limestone and deposited calc-spar on the floor. 

 The number of alternate laj-ers of sjiar and sediment tallied with the years that had elapsed since his 

 first visit ; and, on breaking up the ancient bed of stalagmite, he found the same natural register of 

 the annual variation of the seasons. Every layer dug through presented a uniform alternation 

 of sediment and spar ; and as the botanist ascertains the age of an ancient dicotyledonous tree from the 

 annual circles of growth, in like manner the geologist attempted to calculate the period that had 

 elapsed since the commencement of these ossiferous deposits of the cave ; and, although the inference, 

 from want of time and means to conduct the inquiiy with precision, can only be accepted as a rough 

 calculation, yet it is interesting to learn that the time indicated bj' this natural chronometer, since the 

 extinct mainmalian forms were interred amounted to many thousand 5'ears.* 



The aee of the remains found in ihe caves is the same as that of those found in the honc- 

 caves of Britain, namely, the later pliocene, that iS, subsequent to the glacial epoch. It is remarkable 

 that aR the bone breccias and bone caves throughout the world belong to the same period. They 

 may be called phenomena of the glacial epoch. How or why none have been discovered ajiplicable 

 to the miocene epoch is not easy to account for. The deposit of bone breccias is doubtless still going 

 on in various parts, where rivers disappear in limestone countries ; but I cannot help thinking that 

 the manufactory is less flourishing than it was in times nearer to the height of the glacial epoch. 



It would be a convenience, in considering questions relating to this period of geological historj^, 

 if eeoloffists would — instead of their older and newer Pliocene and Pleistocene formations — give 

 us a nomenclature bearing direct reference to the progress of the glacial epoch — one phrase to 

 indicate its access, another its establishment, and a third its recess. At present its access (although 

 not less important than its recess, seeing that during it the chief changes from miocene to modern 

 types of form probably took place) is scarcely recognised as part of the epoch at all. 



The locality in North America which has supplied the greatest amount of e\idcnce of the former 

 existence there of species of the genus of which we have been speaking, as well as of many 

 other extraordinary extract animals, is the band of tertiary deposits extending, with interrup- 

 tions, in the line of the Missouri and Mississippi, from the northern shore of the Gulf of Mexico 

 to the Arctic Ocean. The most prolific portion lies along the river Missouri, and is known as tlu; 

 " Mauvaises Torres," or Bad I^ands of the hunters. These occur at irregular intervals all along 

 the Missouri, more especially on the Nebraska or Platte River, and the Niobrara and otliers of 

 its tributaries, and ia some places are of great extent. Thej^ are composed mainl}^ of a soft half- 

 formed sandstone or mud stone, which criunbles under a slight pressure, and is washed by the rains 



* Mantell, O. a., " Petrifactions aod their Teachings ; or, a Hand-book to the Gallery of Organic Kcmains in 

 the British Museum." London, 1851. p. 481. 



