CONDITION OF THE BONES. 151 



" On burning the bone, the ash which remains is of a beautiful blue 

 color, owing to the presence of phosphate of iron, which appears to have been 

 infiltrated into the bone froni the marl surrounding the skeleton." 



Dr. Jackson also gave me two or three portions of the animal matter, 

 which possesses the same degree of tenacity as that found in recent bones. 



The preservation of Mastodon bones may be in many instances attri- causes of 



Preserva- 



buted to a ferrugineous impregnation ; but the bones here described contain tion. 



a smaller quantity of iron than other Mastodon bones not in so good a 



state of preservation. Whence we must infer that other circumstances were 



concerned in preventing their decomposition. 



Bones of the Mastodon Giganteus are not usually found in a mineralized Mineraliza- 

 tion. 

 state. There are, however, exceptions to the general fact. Mr. Conrad, in 



speaking of the bones found on the banks of the Neuse in North Carolina, 



says that they were in a mineralized condition. 



There are in my possession a number of silicified teeth, and I have 

 seen others in the collection of the Academy of Natural Sciences. The 

 Shawangunk country has afforded me a very beautiful sjDecimen of silicified 

 os femoris, three feet and a half long. It was found in Orange County, 

 X. T., not far from Newburgh. It is almost as dark as ebony, has a bril- 

 liant exterior, and requires the full strength of a laboring man to lift it. 



In order to form any opinion as to the causes of this difference, we 

 ought, to be acquainted with the situation of the petrified specimens in 

 relation to surrounding minerals. 



The most common of petrifying substances are solutions of lime, silex, Theory of 



Petrifac- 



and iron. Lime and iron are readily soluble in cold water ; but silex is not, tion. 

 although this fluid, in a heated state, is capable of taking up a considerable 

 portion of it. Silex is quite abundant in a great number of soils ; it enters 



