MIDDENDORF ON SIBERIA. 49 
In general the proportion of the Acephala to the conchiferous Gas- 
teropoda may be taken as = 50, as is the case in Greenland, which 
is entirely surrounded by northern currents, and also very nearly in 
Sicily ; whilst in the intermediate region, where the two faunas com- 
mingle, the proportion of the hardy, more enduring Acephala is much 
larger, since they have not only preceded the other southern molluses 
in their migrations, but have also remained longer behind the other 
species wandering towards the north. 
(J. Nu] 
Herr von Mippenporrr’s Geological Observations in StpERTA 
(Geognostische Beobachtungen auf seiner Reise durch Sibirien) 
by G. V. HetmMersen. 
[From the Bulletin de l’Acad. Imp. de St. Pétersbourg, pour 1847, tom. vi. n. 13.] 
Last year M. von Middendorff entrusted to me the geological obser- 
vations which he had collected during his Siberian journey, with the 
request that I should prepare. them for publication in his travels. A 
collection of rocks and petrifactions, now deposited in the Museum 
of the Academy, accompanied the notices, and were used by me in 
preparing my account. The petrifactions will form the subject of a 
separate memoir by Count Keyserling, who has already published a 
very instructive notice of a portion of them in the fifth volume of the 
Bulletin, in which four new species of Ceratites are described. 
These and many Jurassic petrifactions, which were brought with 
them from the river Olenek and some other Jura shells, which M. 
von Middendorff found in rolled masses in the valley of the Taimyr, 
are the most interesting objects in the collection. The Ceratites in- 
dicate a formation, the muschelkalk, which is im general, and more 
particularly in Russia, rare and very slightly developed. Hitherto 
it was only known in the Great Bogdo Mountain in the steppe of the 
Volga, though supposed to occur on Kotelnoi, one of the islands of 
New Siberia, from which the collection of the Mining Institute pos- 
sessed the fragment of a Ceratite. The discovery of these fossils on 
the Olenek entitles us, however, to believe that the muschelkalk is 
not unknown in continental Siberia, and a more precise determimation 
of their mode of occurrence ought to form a leading object of future 
observers in these far northern regions. But the appearance of the 
Jura formation in the extreme north of the Old World deserves par- 
ticular attention. In a short memoir read to the Academy last year, 
I pointed out how much this formation had recently extended its 
limits in European Russia, whereas formerly it was considered a rare 
and sporadic phenomenon. Count Keyserling proved its extent in 
the Petschora land, where it reaches the shores of the Icy Sea; and 
M. von Middendorff’s observations leave no doubt that in Arctic 
Siberia also it stretches perhaps with slight interruptions from the 
Ural to the valley of the Olenek, and there is reason to believe* con- 
* See Keyserling’s Petschora Land. 
