6 BUREAU OP AMERICAN ETHNOLOGY [bull. 52 



mineral substances that adhere; (5) simple mechanical or sedimental 

 filling of the bone cavities by mineral substances; and (6) lithifica- 

 tion, i. e., conversion, more or less complete, of the bone into stone 

 or ore through both infiltration and the replacement by other ele- 

 ments or compounds of the original inorganic constituents of the 

 osseous structure. 



These classes of alterations are but rarely met with isolated or 

 perfect, existing more frequently in various combinations and in 

 various stages of incompleteness. Occasionally also one process 

 may have superseded another, a condition especially apt to appear 

 when the location of the specimen happens to be changed, or when 

 the bone is acted on by water differing in mineral composition from 

 that with which it came previously in contact. 



The nature of the alterations depends altogether on the minerals, 

 particularly those in solution, and perhaps also on the gases which 

 come in contact with the skeletal remains,"^ the bones themselves, 

 though differing to some extent chemically as well as physically, being 

 on the whole fairly constant in composition. The conditions to 

 which any particular bone is subject may be favorable or unfavor- 

 able to its alteration. The unfavorable conditions are those that bring 

 about a rapid destruction of the bone, or a dearth or absence of such 

 agencies as are capable of producing changes in the bone that make 

 for durabihty; the favorable ones are the presence of modifying 

 agencies, while destructive potencies are slow. Bones in dry sand or 

 in a dry crypt, or in peat, where bacteria and fungi can not exist and 

 where neither corrosive hquids nor gases occur, can undergo but 

 little alteration; but if exposed for a time to air, sand blast, growing 

 roots, or to water or gases of corrosive quahties, they will show 

 scaling, erosion, or other forms of loss of substance; in acid soil or in 

 a wet, warm, aerated mold they will disappear; in a limestone 

 cave through which water percolates they will be covered with 

 stalagmite, or cemented with earth, stones, shells, etc., and lose 

 rapidly their organic matter; in a shell-heap or in calcareous ground, 

 or where washed by mineral water or reached by underground water 

 carrying minerals in solution, they will be partially infiltrated with 

 lime and may be lined with and covered by a deposit, their inorganic 

 constitution may be more or less changed and m some cases they 

 will become thorouglily petrified. The rapidity of the various proc- 

 esses is proportionate to the nature, quantity, and facility of access to 

 the bone of the various reagents. 



It follows from what has been shown that alterations of any nature 

 in a bone are first of all indications of the conditions under which the 

 bone has existed or, briefly, of the environment of the specimen, and 



1 See data adduced by Gratacap, L. P., Fossils and Fossilization; in The American Naturalist, xxx, 

 Phila., 1896, 902 et seq.i xxxi, Phila., 1897, 16 et seq. 



