POSTSCRIPT ON DEVONIAN ICHTHYOLITES. 
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priority of names and discovery of certain forms, a very grave geological question is involved in the memoir of M. 
Eichwald, and we must, therefore, in justice to ourselves, say a few words on the true determination of these ich- 
thyolites. Not pretending to be judges of the generic and specific value of all the fragments collected by M. Worth 
and Count Keyserling, we brought a large quantity of them to England, and, aided by that sound ichthyologist Sir 
Philip de Grey Egerton, we transmitted a selection of them to Professor Agassiz. The chief results are here made 
known in the text, and the details are given in the second volume. In the meantime, M. Eichwald wrote the 
memoir alluded to, in which he makes certain comparisons that will, doubtless, astonish M. Agassiz as much as 
ourselves, and indeed we may say all geologists. He cites, for example, from these beds, so truly Devonian, the 
Pleuracanthus tuberculatus, a species never previously found beneath the carboniferous limestone. To a second he 
gives the name of Saurichthys, a genus hitherto known in the Muschelkalk ; whilst a third and fourth he terms 
Hybodus longicornus (Ag.) and Pristacanthus ; genera which Agassiz has recognised in the Lias and Jurassic strata 
only ; whilst even a Pleuracanthus, by which Agassiz characterizes the tertiary molasse, is said by M. Eichwald to 
be here mixed up with true Devonian and Silurian genera ! Again, in adverting to the existence of the Ctenodus, 
M. Eichwald commits the mistakes of saying, that this well-known carboniferous type had hitherto been found in 
the chalk only, and that the Onchus (an Old Red and also a carboniferous genus) had been hitherto detected in the 
Upper Silurian only. In short, if M. Eichwald is right, and the authors of this work and M. Agassiz are wrong, then 
is the deposit on the Slavenka a geological omnibus, wherein creatures of all epochs, from protozoic to tertiary, 
lived together in the very same bed. As such a phsenomenon would, if admitted, subvert all those inductive processes 
by which geologists have been hitherto guided, M. Eichwald must excuse us if, relying on the identifications of M. 
Agassiz and our own views, we entirely deny its existence. We must also state, that the example of St. Cassian 
in the Alps, where, on the authority of Count Munster, palteozoic and secondary forms are said to be mixed toge- 
ther, has no real bearing, as M. Eichwald infers, on this Russian question. In the Alpine case (which has never 
been geologically described) there exist, if we are not misinformed, lofty' and almost vertical mountain escarpments, 
at and near the summits of which one group of formations may very well exist, and another at their base; whilst 
the remains, to which the name of St. Cassian has been applied, are simply those which are collected by the peasants 
from the valley, — fossils which have fallen from various heights and are necessarily mixed together below. On 
the Slavenka, on the contrary, the supposed melange occurs in one and the same stratum. 
We need scarcely add, that beyond the lithological features described, there is not on the Slavenka, any more 
than on theVolkof or Siass, the smallest evidence of transition from the Lower Silurian to the Devonian fish-beds, 
as asserted by M. Eichwald ; still less of any intermixture of the fossils of the two groups, except where the strata 
have been broken up, and their surface affected by the northern drift (see Chapters XX. and XXL). If such a 
transition and passage were admitted, we might in Russia cite many other equally apparent examples of such, — 
as between the carboniferous limestone and Jura rocks of Moscow (p. 235), or the Permian rocks of the Vaga 
and their overlying pleistocene beds! (p. 331.) But such an idea requires no serious refutation, and geologists 
must rest contented with our distinct and unequivocal denial of M. Eichwald’s supposed facts; whilst M. Agassiz 
assures them, that the fishes in this Russian deposit (which we affirm is true Devonian) are either well-known types 
of the Old Red Sandstone only, or forms hitherto never found in any other overlying or underlying deposit. 
Postscript on Devonian Fossil Fishes.— The geological student will soon perceive, that the ensuing chapter 
on the Devonian rocks was written and printed without the knowledge of the ichthyolites of that age commu- 
nicated to us by Professor Agassiz, whilst preparing the opening chapters of this work, which, for reasons before 
assigned, were the last sent to press. Whatever changes of names that author may have ultimately applied to 
the Devonian ichthyolites (for which we refer to our preceding observations and to his descriptions in the second 
volume, or in his ' Monographic des Poissons du SystSme De'vonien ou Vieux Gres Rouge’), our readers will find 
