Fossil Organic Remains. SI 
at the present day. On the coast of Terra Firma, between 
Cumana and Nueva Barcelona, I have seen crocodiles advance 
far into the sea. Pigafetta has made the same observation re- 
garding the crocodiles of Borneo. To the south of the Island 
of Cuba, in the Gulph of Xagua, there are lamantines in the 
sea, at a point where springs of fresh water issue in the midst 
of the salt water. When we reflect upon these facts, we be- 
come less surprised at the mixture of some terrestrial produc- 
tions with many others indisputably marine. The second case 
which w r e have adverted to, that of alternation, is never present, 
I believe, in a manner so distinct as the alternation of clay-slate 
and of black limestone, in the same transition formation, or (to 
adduce a fact relative to the distribution of organic bodies) as 
the alternation of two great marine formations, (limestone with 
cerithia, and the sandstone of Romainville), with two great fresh- 
water formations, (gypsum and millstone of the plain of Mont- 
morency). The result of an attentive examination of the super- 
positions is merely this ; that there are alternating beds of gyp- 
sum and marl placed between two marine formations, and con- 
taining at the centre (in their largest mass), terrestrial and 
fresh-water productions, and towards the upper and inferior 
limits, as well in the gypsum as in the marls, marine produc- 
tions. Such is the geological constitution of die gypsum of 
Montmartre. The specific variation in the petrifactions, the 
mixture observed at Pierrelaie, and the phenomenon of alterna- 
tion which Montmartre presents, are not sufficient to justify the 
division of the same formation into fragments. The marls and 
gypsum which contain marine shells, (No. 26. of the third 
mass), cannot be geognostically separated from the marls and 
gypsums which contain fresh-water productions. Nor have 
Messrs Cuvier and Brongniart hesitated to consider the general 
mass of these marine and fresh-water marls and gypsums as of 
one and the same formation. These geologists have even cited 
this union of alternating beds as one of the clearest examples of 
what the word formation should be intended to express. ( Geogr . 
Miner. y p. 31, 39, 189). In fact, different systems of beds 
may be contained in the same formation : they are groups, sub- 
divisions, or as the geognosts of the Freyberg School express it. 
