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Ch. XLVL] 



IN SUBAQUEOUS DEPOSITS. 



535 



volume ; so that when first killed tliey do not sink to the 

 bottom like quadrupeds^ but float on the surface until the 

 carcass either rots away or is devoured by predaceous animals. 

 To these causes we may ascribe the absence of any vestige 

 of the bones of birds in the recent marl formations of Scotland ; 

 although these lakes^ until the moment when they were artifi- 

 cially drained^ were frequented by a great abundance of water- 

 fowl. 



IMBEDDING OF TEEBESTBIAL QUADBTJPEDS. 



Eiver inundations recur in most climates at very irregular 

 intervals, and expend their fury on those rich alluvial plains, 

 where herds of herbivorous quadrupeds congregate together. 

 These animals are often surprised ; and, being unable to stem 

 the current, are hurried along until they are drowned, when 

 they sink at first immediately to the bottom. Here their 

 bodies are drifted along, together with sediment, into lakes or 

 seas, and may then be covered by a mass of mud, sand, and 

 pebbles, thrown down upon them. If there be no sediment 

 superimposed, the gases generated by putrefaction usually 

 cause the bodies to rise again to the surface about the ninth or 

 at latest the fourteenth day. The pressure of a thin covering 

 of mud would not be sufficient to retain them at. the bottom ; 

 for we see the putrid carcasses of dogs and cats, even in rivers, 

 floating with considerable weights attached to them, and in 

 sea-water they would be still more buoyant. 



Where the body is so buried in drift-sand, or mud accumu- 

 lated upon it, as never to rise again, the skeleton 

 preserved entire ; but if it comes again to the surface while 

 in the process of putrefaction, the bones commonly fall 

 piecemeal from the floating carcass, and may in that case be 

 scattered at random over the bottom of the lake, estuary, or 

 sea ; so that a jaw may afterwards be found in one place, a 



mav 



humerus 



— all included, perhaps, 



in a matrix of fine materials, where there may be evidence 

 of very slight transporting power in the current, or even of 



some 



mals, if 

 climates 



h ^ 



