1895.] Fluorine as a Test for the Fossilization of Animal Bones. 447 
It is otherwise for the fluorine, and in spite of the great 
variations in the proportions of this mineral remarked in the 
bones of the same period belonging to deposits in different lo- 
calities, it does appear that we may formulate a general law of 
age based upon the increase in the proportion of fluorine ex- 
isting in them. This law is shown with greater certainty and 
clearness in the comparison of the average proportions in the 
entire number of specimens from each geologic epoch than 
from the proportions in the individual specimens, and in 
order to render this more apparent, the table following of geo- 
logic epochs shows the average results obtained from the 
bones of each one of these periods. The first column gives the 
average proportion (as above calculated) of fluorine to that of 
an apatite containing the same quantity of phosphoric acid. 
The second column gives the average ratios of the weightjof 
phosphoric acid to the weight of fluorine. 
he ratio between The ratio of the 
: : 7 weight o 
Geologic Periods. jho quantity ofin phorie acid in the 
to that of apatite. bone to that of flu- 
Modern «.......0cc.ccscesseveresscees 0.958 0.058 193.1 193.1 
paring vinta sien evesecseecseses 0.36 0.360 31.3 31.30 
ertiary sssi 
pliocëne........sesooe.sss roosa ee ) 19.2 | 
miocene x 18.3 z 
Aa oa ae nics 0.59 j poen 189 ů 1815 
ONE 0.70 16.0 | 
Secondary. 
cretaceous 0.92 12.2 : 
JUTASSİC. nesset eeeeeeeeses tettet 0.41 > 0.907 12.3 } 12.40 
ba triassic. 0.89 12.6 
mary. 
aes vanced 1.06 10.5 
devonian.. -. ib ans 0.98 0.993 11.4 11.30 . 
SULUTIBN: cssese esses 2c ctcsshens 0.94 120 
Apatite normal 1.00 — 1.000 11.21 1121 
The averages set forth in the figures of this table are not to 
be taken as of absolute, but only as of relative, value. The 
only ones which can be considered definite are those relative 
to apatite on the one side and to the modern bones on the 
other. For the fossil bones, the average not only varied with 
