4G Art of making Gun-Flints. 
begins to be decomposed. He offers a quer y* whether 
the difference may not consist in the small portion of 
combustible or fatty matter* which caused the detonation 
with nitre* or whether the quartz may not* like alum* ac- 
quire its property of crystallizing from the addition of 
some other substance. This question* as he remarks* 
must be resolved by future experimental enquiries. 
The analysis of the whitish spots afforded silex 98 
grains* oxide of iron 1* carbonate of lime &. That of the 
absolutely opake parts gave five parts more of carbonate 
of lime ; and lastly* the analysis of the white coating na- 
turally enveloping the masses* afforded 86 parts of silex, 
1 oxide of iron* 10 carbonate of lime* and 3 loss. Those 
analyses which afforded no alumine* shew that this earth 
is not essential to the silex* and the absence of lime in the 
first analysis shews that it was an accidental ingredient in 
the latter. 
Mineralogical situation. In France in the environs of 
St. Aignan* situated in the department of Loir-Cher* and 
in that of LTndre* and the departments which occupy the 
vallies of Siene and Marne* are principally the places 
where this stone is found. It exists in the chalky calcare- 
ous stones* in chalks more or less fine and solid* and in 
inarles. They form horizontal strata* by the manner in 
which the large and small masses are placed beside each 
other. Nevertheless* as the blocks of silex do not accu- 
rately touch each other* there is no solution of continuity 
between the upper and lower masses of chalk. 
Out of twenty beds of silex lying one above the other* 
at a distance of twenty feet or less* there will frequently 
be no more than one* and very seldom two* which afford 
good stones of this description ; but in the bed which af- 
fords them* almost all the blocks have a greasy appearance* 
and in the other strata scarcely any of this description 
will be found. Accordingly the good strata are followed 
