16 GEOLOGICAL MEMOIRS. 
when it remains fixed, and a new septum is formed close on the 
former, which is moved forward in a similar manner. . This mode of 
imcrease reminds us of some inorganic formations in which deposition 
on the one side is conjoined with solution on the other. Even in the 
large Ammonite the last chamber visible is considerably smaller than 
the previous ones. A second Orthoceratite, not seen in the plate, is 
found on the corner of the slab, and belongs to another species. A 
third, of which a cross section is visible, appears near the side, the 
rather excentric siphon being distinctly recognizable. 
Further we find, and all on the same side with the large Ammo- 
nite, forty to fifty smaller Ammonites, from a line to three inches in 
diameter, which belong to various species, the most common being 
the 4. galeatus, then the A. tornatus, Broun, whilst many others, 
from their imperfect preservation, are no longer to be determined. 
A third genus of Cephalopod, the Belemnites, is found on this 
remarkable slab in considerable abundance, one of them being repre- | 
sented in the figure. This confirms a statement of Von Lill which 
has often been doubted. The species of these Belemnites cannot 
however be determined till other specimens render a more accurate 
examination possible. 
On the same specimen are many Gasteropods which cannot be 
determined, then bivalves, among which is a tolerably distinct Nucula, 
and lastly a multitude of crinoidal stems and many other organic 
remains whose true nature has not yet been made out. 
This specimen was found on the summit of the Stembergkogel 
near Hallstatt by M. Ramsauer. On the age of the formation in 
which it occurs geologists and palzeontologists have expressed various 
opinions, of which only the more recent, by a few distmguished 
naturalists, require to be noticed. Lill v. Lihenbach, whose two 
sections in the northern Alps must still be classed among the best 
geological works on this region, depending chiefly on petrographical 
grounds, considers this formation as jurassic. Professor H. Bronn, 
who examined accurately the petrifactions collected by Von Lill, is 
of opinion it must be classed in the lias, which here however con- 
tains transition fossils (Uebergangs-Petrefacten). Professor Quen- 
stedt finally, who has himself visited the district of Hallstatt, 
examined the rich collections of MM. Ramsauer and F. Simony, and 
himself collected a great number of its fossils, and at a later period 
obtained others from M. P. Mohr, believes himself justified in de- 
claring these beds to be the lower chalk or Néocomien. 
On pure paleontological grounds either of these analogies may 
justly be preferred to the others; and if, for instance, Prof. Quen- 
stedt assumes that the species of the transition period had here anew 
revived in the chalk, we may with equal probability assert that forms 
peculiar to the chalk had in the Alps already existed in the Jurassic 
or Lias epoch. 
Perhaps it would be expedient, before attempting to assign to the 
particular deposits of the Alps a special place in the series of strati- 
fied formations as they exist in other parts of Europe, to study with 
more exactness each of the deposits in this chain and the petrifac- 
