668 
difficult of solution, and which continue to raise doubts in the 
minds of the best and most experienced observers. In their de- 
scription of the rocks, the authors, faithful to what may be called 
the “ natural method,” have classed together all those which appear 
to have a common origin, such as granites, porphyries, basalts, tra- 
chytes, &c. 
In short, the geological map of France, and the volumes of ex- 
planation to accompany it, will form one of the finest monuments 
raised to science in our era, and must be constantly consulted by 
those who wish to understand the spirit of that school of geology, 
which has cast such a brilliant light over France and throughout 
Europe. Doubly grateful indeed is the production of the work to 
ourselves, for in presenting it to this Society its authors have 
assured us that it was in our own islands they first acquired that 
knowledge of classification which led them to attempt the great 
enterprise, the completion of which so well sustains the high repu- 
tation they enjoy. Further, when we recollect that the knowledge 
of our foreign associates was one of the first fruits of the general 
peace, well may we now view the noble structure they have reared 
upon such a basis, as a convincing proof of the advantages con- 
ferred on science by the friendly intercourse of nations, which now 
rival each other only in advancing science and art! 
Another most important work undertaken in France during the 
last year, is ‘La Paléontologie Francaise’ of M. Alcide d’Orbigny. 
Early initiated into the study of organic bodies and the anatomy of 
mollusks, this naturalist has acquired, during his extended travels, a 
good knowledge of positive geology ; and he is therefore peculiarly 
qualified to carry into effect his arduous enterprize of describing 
the fossils of France in the order of the formations. He has com- 
menced this vast undertaking by publishing during last year 139 
plates, and upwards of 500 pages of text, on the Cephalopods of the 
Chalk. It is only necessary to glance over the figures, to perceive 
the care with which the different parts of the fossils are delineated. 
I particularly recommend to your notice the new genera, named by 
M. d’Orbigny “Ancyloceras” and “ Towoceras,’ and which added 
to the “Crioceras,” recently introduced into the science, increase 
that infinite variety of forms in which the great Ammonite family 
expanded, previously to its total disappearance from the living 
world. - 
The Cephalopods, very rare in the upper beds of the chalk, oc- 
cur in such prodigious quantities in the lower parts, and particularly - 
in the “ Neocomian”’ group, as defined by continental geologists, 
that they occupy all the Numbers hitherto published of the ‘ Palé- 
ontologie Francaise. The Ammonites have heen the object of espe- 
cial study to M. d’Orbigny, and have led him to conclusions of the 
highest interest, both zoological and geological. In the former 
respect, his observations on the external characters of Ammonites, 
and on the limits of their natural and accidental varieties, of the 
differences of sex, and particularly of age, are entirely original. 
Following these remains through the period of their development, 
