254 
THE GEOLOGIST. 
In consequence of tlie destruction of the bony substance, the car- 
bonate of lime ought to augment in a fossil bone, but this does not 
always take place. In certain fossil- human skulls it falls more than 
three per cent, although it is at least double in a normal skull : the 
quantity of carbonate of lime diminishes, therefore, occasionally, in 
fossil bones, more particularly in the first period of their decomposi- 
tion, that is, when the bony substance is being destroyed. 
But most frequently the carbonate of lime augments in the fossils 
prior to our epoch. One can easily prove this in those which are 
cellular, because their cavities are filled with it in a crj^stallized form. 
It also increases in the most compact bones, even the teeth and tusks. 
As the carbonate of lime is found in most rocks and waters of infil- 
tration, it is easy to understand why its quantity increases in fossil 
bones. The phosphate of lime sometimes diminishes considerably, 
as low as twenty-five in one hundred, as M. Fremy has proved ; 
sometimes, on the contrary, it rises as high as eighty in one hundred, 
although on the average it is little over sixty in the normal state. 
The bony substance is present in fossils, and the azote they contain 
enables us to arrive at the proportion. ^Nevertheless, but little remains 
in the bones found in formations older than the tertiary. The bones 
which belong to the recent formations, or to the diluvium, contain, on 
the contrary, a good proportion. 
The quantity of azote in a fossil bone depends on complex causes. 
Firstly, it varies with the bone and the animal. Nevertheless, when 
one compares the bones of mammals, birds, and reptiles, the difference 
in the proportion of bony substance does not exceed many hundredth 
parts, consequently the difference of proportion of azote is reduced 
to some thousandth parts. 
When the bones are fossilized, the azote depends on their exposure 
to the atmosphere before they were covered up ; for the atmosphere 
destroys organic matter pretty rapidly. It depends also upon the 
dampness or dryness of the beds in which they lie, and upon the salt 
or fresh -water which they imbibe. The mineralogical composition of 
the rock in which they are found must again be considered, because 
it tends to vary the substances contained in the water of infiltration. 
Lastly, the azote in a fossil bone varies with the age. To be con- 
vinced of this fact it will be enough to test it in bones belonging to 
different epochs, and especially in human bones. Although a normal 
bone contains about fifty-four thousandths of azote, there are but 
32*3 in a human bone more than a century old ; 22'9 in one of the 
time of Julius Caasar ; I8'5 in a human skull found by Sir C. 'Lyell 
in the Denise beds ; 16*5 in a human jaw-bone, which has been for- 
warded to me by M. de Yibraye, as coming from the gTotto of Arcy, 
and 13-6 in a human cubitus discovered by M. Lartet, at Aurignac. 
The human remains last mentioned have been the subjects of much 
geological discussion ; they are regarded as very ancient, and, as we 
have seen, contain but little azote. Nevertheless, in other human 
bones which have undergone changes, either by exposure to air or by 
fossilization, the proportion of azote is still less. A human skull, of 
