120 LAMAKCK, HIS LIFE AND WORK 
actual maximum of this process of perfecting, the 
limit (¢erme) of which, if it exists, cannot be known.” 
In the fourth chapter of the book there is less to 
interest the reader, since the author mainly devotes 
it to a reiteration of the ideas of his earlier works on 
physics and chemistry. He claims that the minerals 
and rocks composing the earth’s crust are all of 
organic origin, including even granite. The thick- 
ness of this crust he thinks, in the absence of positive 
knowledge, to be from three to four leagues, or from 
nine to twelve miles. 
After describing the mode of formation of minerals, 
including agates, flint, geodes, etc., he discusses the 
process of fossilization by molecular changes, silicious 
particles replacing the vegetable or animal matter, as 
in the case of fossil wood. 
While, then, the products of animals such as corals 
and molluscs are limestones, those of vegetables are 
humus and clay; and all of these deposits losing their 
less fixed principles pass into a silicious condition, and 
end by being reduced to quartz, which is the earthy 
element in its purest form. The salts, pyrites, and 
metals only differ from other minerals by the different 
circumstances under which they were accumulated, in 
their different proportions, and in their much greater 
amount of carbonic or acidific fire. 
Regarding granite, which, he says, naturalists very 
erroneously consider as primztive, he begins by ob- 
serving that it is only by conjecture that we should 
designate as primitive any matter whatever. He 
recognizes the fact that granite forms the highest 
