34 Mr Davy's Lecture on the Decomposition and Composition 
to show,* may contain both saline and metallic impregna- 
tions ; and the free atmosphere almost constantly holds in 
mechanical suspension solid substances of various kinds. 
In the common processes of nature, all the products of 
living beings may be easily conceived to be elicited from 
known combinations of matter. The compounds of iron, of the 
alkalies, and earths, with mineral acids, generally abound in 
soils. From the decomposition of basaltic, porphyritic,-f and 
granitic rocks, there is a constant supply of earthy alkaline and 
ferruginous materials to the surface of the earth. In the sap of 
all plants that have been examined, certain neutrosaline com- 
pounds, containing potash, or soda, or iron, have been found. 
From plants they may be supplied to animals. And the che- 
mical tendency of organization seems to be rather to combine 
substances into more complicated and diversified arrange- 
ments, than to reduce them into simple elements. 
The conclusions which M. Bracon not has very lately drawn from his ingenious 
experiments, Annales de Chemie, Fevrier 1 807, page 1 87, are rendered of little avail in 
consequence of the circumstances stated in the text. In the only case of vegetation 
in which the free atmosphere was excluded, the seeds grew in white sand, which is stated 
to have been purified by washing in muriatic acid ; but such a process was insufficient 
to deprive it of substances which might afford carbon, or various inflammable matters. 
Carbonaceous matter exists in several stones which afford a whitish or greyish powder ; 
and when in a stone, the quantity of carbonate of lime is very small in proportion to 
the other earthy ingredients, it is scarcely acted on by acids. 
* Bakerian Lecture, 1806, page' 8. 
f In the year 1804, for a particular purpose of geological enquiry, I made an 
analysis of the porcelain clay of St. Stevens, in Cornwall, which results from the 
decomposition of the feldspar of fine-grained granite. I could not detect in it the 
smallest quantity of alkali. In making some experiments on specimens of the 
undecompounded rock taken from beneath the surface, there were evident indica- 
tions of the presence of a fixed alkali, which seemed to be potash. So that it is very 
probable that the decomposition depends on the operation of water and the carbonic 
acid of the atmosphere on the alkali forming a constituent part of the chrystaliine 
matter of the feldspar, which may disintegrate from being deprived of it. 
