CAUSES OF PRESERVATION. 161 



skeletons known to exist have been discovered in this region, — the 

 two procured by Mr. Peale, and that here described ; a fourth, that of 

 the University at Cambridge, was buried near the sources of the Wa'alkiL 

 Besides these skeletons, various deposits, in ten or twelve different locali- 

 ties, have been found scattered about a region in the vicinity of these 

 streams. 



In nearly all these different spots, the bones have lain at the depth 

 of from five to ten feet below the surface. The same fact is true of deposits 

 near Niagara, described by Sir Charles Lyell ; of those in Virginia, Long 

 Island, the salines of Ohio, Kentucky, and most other places in the Western 

 and Southern country of the United States. 



The overlying deposits are generally a foot or two of mud, the same overlying 



Deposits. 



thickness of clay, a layer of peat sometimes intervening, and below the clay 

 shell-marl containing everywhere the relics of fresh-water testacea of exist- 

 ing species ; some of them perfect, others decomposing. Sir Charles Lyell, 

 in his geological tour through the State of New York, found, at Genesee, 

 the bones of the Mastodon in a bed of shell-marl below the peat, cor- 

 responding, he remarks, with the situation of the fossil elks of Ireland, EossiiEik. 

 generally considered to have been buried in bog-mud or peat-swamps, but 

 which in fact lie in a stratum of shell-marl. 



I have in my possession the head of a fossil elk in a silicified state ; 

 for which I am indebted, through the influence of the distinguished Dr. 

 Houston, of Dublin, to the liberality of the Royal College of Surgeons, of 

 that city. This head is decidedly silicified to a greater degree than bones 

 of the Mastodon skeleton usually are ; but it is not uncommon to find well- 

 silicified bones ; and the femur, already alluded to, is more fully petrified 



than the head of the Irish elk. Probably the relics of these two animals 

 21 



