64 UNION OF OLD RED FISHES AND DEVONIAN SHELLS. 
in the Silurian rocks. On the other hand, Trilobites, which are so profusely dis- 
tributed in the Silurian rocks of the Baltic governments, are of very unusual occur- 
rence in the Devonian strata. 
But the greatest distinction of all, between these Devonian beds and those on 
which they repose, is the profusion of ichthyolites, none of which are found in the 
lowest fossiliferous system of Russia 1 . 
In Polypifers, the Devonian rocks of the northern and central districts are not 
rich, as might be expected from the sandy, marly and flag-like nature of the strata ; 
but on travelling to the confines of Asia, we find that beds of the same age in 
the Ural Mountains, having the subcrystalline, slaty and calcareous facies of the 
rocks of Devonshire, are like them loaded with corals. Nay more, these polypifers 
are associated with several species of mollusks identical with those of the British 
Isles, whilst the agreement between these very distant synchronous deposits is still 
further maintained by the negative feature common to both, of the absence of 
ichthyolites. 
The connexion between the character of the fossils and the nature of the matrix 
in which they are imbedded, is, indeed, more pointedly brought before the observer 
who ranges over the boundless tracts of Russia, than in any other country which 
it has been our lot to examine. In Courland, Livonia, and the Baltic governments, 
as well as in the great central region to which the system extends, thin beds of 
finely laminated limestone alternate with and are subordinate to great masses of 
sand, marl and flagstone ; and whilst in the thin limestones mollusks prevail, occa- 
sionally mixed up with the remains of fishes, the latter are often found exclusively 
in marly and sandy beds. 
Now in tracing these rocks from the Baltic provinces on the south-west, towards 
Archangel on the north-east, the limestones (as stated p. 48) gradually thin out, 
and the system (as in the government of Olonetz) being represented by sand, clay, 
and sandstone, w r e there lose the Mollusca, and find that the rocks having the 
essential characters of the Old Red Sandstone of Scotland are, like that deposit, 
inhabited by fishes only ! A remarkable phenomenon, in showing an accordance 
1 In Great Britain, where the Silurian system is so copiously developed, no ichthyolites have been 
discovered by the authors beneath its uppermost member — the Ludlow rocks ; but very recently palates 
of a fish have been discovered by the Rev. P. B. Brodie, near Dursley Cross, May Hill, Gloucestershire, 
in strata which are referred to the Wenlock limestone. It is possible that ere long some trace of ichthy- 
olites may be found in the upper part of the Silurian rocks of Russia. 
