1816.] Mr. B. Prevost on Dew. 127 
as the unequal sinking is a consequence of the unequal contraction, 
the phenomenon of formations must be “a consequence of the 
unequal contraction of the earth’s matter.” 
Having now finished what I proposed, I will close these essays 
with some general remarks on stratified formations. I consider the 
great formations, namely, the sand-stones and coal formations, to 
be formed in the manner that lakes are at present filling up. The 
sand-stones are large Lars deposited by former rivers at the places 
where they entered former lakes, and the coal formations are the 
sediments of these lakes. 
I scarcely need remark how well the position, relative situation, 
and the nature of these formations, accord with this idea; nor need 
I show with what facility this theory at large accounts for the exist- 
ence of entombed marine animals so high above the present ocean ; 
nor why these bodies are in general confined to lime-stone, the 
large vegetables to the sand-stone, and the small to the coal forma- 
tions ; as these phenomena admit of the easiest and clearest expla- 
nation upon the prineiples displayed in these essays. 
ArticLteE XI. 
Extract of a Letter from Mr. Benedict. Prevost, Professor at 
Montauban, to Mr. Pierre Prevost, Professor at Geneva, re- 
specting the Dew which is deposited on that Side of Panes of 
Glass where the Air is coldest. 
(To Dr. Thomson.) 
SIR, . 
Tue annexed abstract of a letter from Mr. B. Prevost relates to 
a fact which has been discussed in your Journal (vol. vi. p. 379, 
432).* I think your readers will consider it as necessary to com- 
plete the discussion in question, 
Iam, &c. 
(Signed) * P. Prevost. 
Geneva, Jan, 1816. 
As to the humidity which is deposited on the outside of a glass 
pane, though the air on the outside be colder than that within, I 
am certain that I have observed it several times, pretty frequently 
indeed. 1 mean that I have observed this humidity on the outside 
when the external thermometer was lower than the internal. But 
you know, my dear cousin, and you state it yourself (at No. 24 of 
your § 192, p. 241), that I endeavoured to procure thermometers 
with flattened bulbs, and sufficiently sensible to point out the diffe- 
* Sce also the present Number, p. 
5 
