Formations in the neighbourhood of Castellane. 161 
tions observed in the exterior configuration, it was necessary 
to examine with care the modifications of internal structure 
which these fossils present, to determine the differences aris- 
ing from the age of the animals to which they belonged, and 
to endeavour to ascertain the limits of the variations to which 
individuals of the same species are subject, in consequence of 
the circumstances in which they have lived, or the accidents 
to which they have been exposed. Many naturalists have col- 
lected observations on this subject, more or less precise ; M. 
de Blainville, M. Voltz, and M. @Orbigny, for example ; but 
the small number of specimens which these gentlemen had 
generally at their disposal did not permit them to carry their 
researches so far as they would unquestionably have done, had 
materials been supplied to them. The author of the memoir 
now under examination, was placed in more favourable cireum- 
stances ; and skilfully availing himself of the paleontological 
riches with which his mountains supply him in profusion, he has 
been enabled to add new facts to those already known, and to 
solve in an explicit manner an important part of the questions 
hitherto unanswered. The vicinity of Grasse, where M. Duval 
is established as a professor of philosophy, is one of the locali- 
ties where Belemnites are found in the greatest abundance; 
and during the ten years that this observer has applied himself 
to the study of these bodies, he has not ceased to explore the 
various strata of the lower cretaceous formations in which they 
are found, both in the north-west portion of the Department 
of Var, and in that bordering on the Lower Alps, near Cas- 
tellane. M. Emeric, who inhabits the same district, and who 
likewise actively devotes himself to paleontological pursuits, 
has furnished him with a valuable collection, so that our au- 
thor has had at his disposal not fewer than upwards of ten 
thousand individuals. It has been easy for him, therefore, to 
follow step by step the changes produced by growth in the 
form and structure of these curious shells; to multiply as 
much as he pleased sections for the purpose of shewing the 
arrangement of their constituent parts, and to appreciate the 
value of the variations remarked in them. We cannot, with- 
out encroaching too far on the time of the Academy, follow 
M. Duval step by step in his exposition of the results to which 
VOL. XXXII, NO, LX1IT.—JANvuARY 1842, L 
