408 C. T. Jackson's Analysis 
have its animal matter replaced by mineral elements. This is 
not necessary to constitute a fossil ; for, under favorable cir- 
cumstances, animal matter in bones may be preserved for an 
indefinite length of time. 
When an animal is buried in sandy soil, through which rain 
water freely percolates, the animal matters are quickly decom- 
posed, removed by solution, and by a slow combustion or ox- 
idation, effected through the agency of the oxygen gas of the 
air, dissolved in the water, there being about twenty per cent. 
in bulk of oxygen gas dissolved in rain water. If, on the 
other hand, an animal is buried in clay or marl, but little wa- 
ter can flow through it, and air does not gain free admission ; 
hence the animal matters remain in the bones, and even the de- 
composed flesh remains in the form of a black mould around 
the bones, and the clay has a strong odor of animal matter. 
In the tertiary clay marls of. Westbrook, Gardiner, Augusta; 
Bangor, Lubec, South Berwick, and Kittery, in Maine, the 
membranous matter forming the epidermis of extinct species 
of shells, remains undecomposed, and the clay has a strong 
smell of sulphureted hydrogen gas, like that of ordinary dock 
mud. [n some cases, the animal matter of the epidermis of 
the shells has proved more permanent than the carbonate of 
lime of the shells, which is not unfrequently removed by the 
acids in the clay, leaving the form of the shell perfectly repre- 
sented by its membrane and mould in the clay. 
When the skeleton of the seal was dug up in the clay marl 
of South Berwick, from a depth of thirty feet, the workmen 
noticed a black mould surrounding the bones, and a strong 
smell of animal matter was perceptible in the clay. 
If animal matters are so well preserved in the tertiary de- 
posits, it will not appear strange that the bones of animals n 
the more recent deposits should have preserved their animal 
tissues. : 
The bones which I have analyzed are those of the American 
mastodon. A quantity of the chips of bone cut from near the 
second molar tooth of the jaw of a young mastodon, belonging 
