667 
to survey those points which required their conjoint examination, 
and by this means they finally established a perfect agreement in 
all the parts of their great undertaking. During the last five or six 
years, since the main features of the map were completed, the re- 
sults have been communicated to every geologist who sought in- 
formation, as I myself have experienced in my visits to Paris; and 
the authors, accepting in the mean time the contributions of others, 
have brought the map to its present degree of perfection. 
Wishing to popularize geology in France, and to give their la- 
bours an extended sphere of usefulness, Messieurs de Beaumont and 
Dufrénoy have published, with the first volume of explanations 
which accompanies the large map, one on a reduced scale, giving an 
exact idea of the disposition of the mineral masses, and facilitating 
the comprehension of the admirable descriptive memoirs contained 
in the volume. 
A desire has been often expressed, as you know, that all geolo- 
gists might come to an understanding on the choice of colours, so 
that geological maps might be a sort of book written in a universal 
language. This idea, as our own great geological geographer Mr. 
Greenough has found, is more plausible in theory than practicable. 
In the selection of their colours, I confess, I regret that our foreign 
associates have not employed the normal colours used in the map of 
England, but then we must recollect that the principle of their co- 
louring was decided and put into execution long before the publi- 
cation of Mr Greenough. ‘The authors of the French work have 
however done well in giving one colour only to each great natural 
division of rocks, and they have distinguished the subdivisions by 
conventional signs, in a similar manner to that employed in the map 
of the Silurian region and Mr. Greenough’s map of England. The 
advantage of this certain method of showing the relations which 
exist between the different parts of the same formation, is now 
thoroughly recognised. : 
Under the modest title of explanation of the map, the authors 
will publish three quarto volumes, of which the first only has yet 
appeared, and judging from this specimen we have a right to con- 
clude that they will form one of the most splendid and usefui works 
ever executed on the geology of a-great country. In the intro- 
ductory chapter of the published volume the general principles of 
the science are admirably given, and the succeeding chapters are 
occupied by descriptions of the “ Massif central de la France: 
Presqwile de Bretagne, Ardennes: Vosges: Montagnes littorales du 
Département de Var: Terrains Houillers.” The authors have di- 
vided their descriptions into great geographical regions, beginning 
with the most ancient formations; and I cannot resist expressing 
how much pleasure it has given me to see that these eminent men 
have adopted the divisions and nomenclature which have been 
proposed for the paleozoic rocks of England. In the other volumes 
the authors will describe the more recent formations, reserving for 
the conclusion, the account of those parts of France where the ele- 
vated and dislocated sedimentary deposits present problems most 
