362 
SILURIA. 
[Chap. XIV. 
remarkable form, but also of other well-known genera of the Caithness Flags — 
Osteolepis, Diplopterus, and Dipterus. The other Scottish forms, and even 
species, found by myself and companions, were, indeed, long ago identified by 
Agassiz and Owen as having their exact representatives in Russia. Such are 
the great Asterolepis (Chelonichthys) Asmusii, Ag., and the smaller species A. 
minor, Ag., with Glyptosteus favosus, Ag., Bothriolepis ornata, Eichw. (Glyp- 
tosteus reticulatus, Ag.), Holoptychius nobilissimus, Ag., Dendrodus strigatus, 
Owen, D. biporcatus, Owen, Cricodus incurvus, Ag. (Dendrodus, Owen), Pte- 
richthys major, Ag., &c. *, — all belonging to the central portion of the deposit 
in Scotland t (see also p. 262). 
When my colleagues and myself explored Russia, the connexion between the 
character of the fossils and the nature of the matrix in which they are im- 
bedded was more pointedly brought before us in our range over that vast 
Empire than in any other region with which we were acquainted. In Cour- 
land, Livonia, and the Baltic Governments, as well as in the great central dome- 
like region of Orel, to which the formation extends, and where it has since been 
examined and ably described by General Helmersen, finely laminated limestones 
alternate with, and are subordinate to, great masses of sand, marl, and flagstone ; 
and whilst in the calcareous courses Mollusks prevail, mixed with remains of 
Fishes, the latter are found most generally in sandy and marly beds. In tracing 
these rocks from the Baltic Provinces to the White Sea and Archangel, the lime- 
stones thin out, and the group is there represented only by sands and marls. 
Accordingly we find that where the Russian rocks have the sandy character 
of the Old Red Sandstone which in Scotland and a large part of England re- 
presents the Devonian group in the British Isles, they are exclusively tenanted by 
Fishes, — a remarkable proof of the accordance between the lithological character 
and organic contents of rocks of the same age in distant countries. 
Another and not less remarkable fact brought out by the survey of Russia is 
that the species of fossil Fishes well known in the middle and upper portions 
of the Old Red of Scotland, and which in large tracts of Russia lie alone in 
sandstone, are in many other places found intermixed in the same bed with 
those Shells that characterize the group in its slaty and calcareous form in De- 
vonshire, the Rhenish country, and the Boulonnais. This phenomenon, first 
brought to light in the work on Russia by myself and colleagues, demonstrates 
more than any other the identity of deposits of this age, so different in litholo- 
gical aspect, in Devonshire on the one hand, and in central England and Scotland 
on the other. The fact of this intermixture completely puts an end to all dispute 
respecting the exact correlation of the chief masses of the Old Red Sandstone 
of Scotland with the calcareous deposits of Devonshire, the Eifel, and the 
Rhenish Provinces. As this circumstance had been slightingly spoken of, I 
wrote to my colleague, Helmersen, to enable me to reassert the fact on his own 
knowledge, and he assured me that this intermixture of Fishes and Mollusks 
is visible in numerous parts of Russia, and that any person who may be scep- 
tical has only to visit the Museum of the Imperial School of Mines to see 
* ' Kussia-in-Europe,' vol. i. p. 40, and fig. termed Asterolepis by Eichwald. (See, however, 
p. 636. Sir P. Egerton's remarks on the subject in the 
t The great work of Pander is a singularly valu- Quart. Journ. G-eol. Soc. vol. xvi. p. 122.) 
able contribution to Palichthyology. The author M. Pander had evidently studied a great num- 
adopts M'Coy's term of ' Placoderms ' to denote a ber of specimens of Asterolepis (Pterichthys) and 
family composed of the genera Asterolepis, Eich- Coccosteus with extreme care. He gives restora- 
wald, Coccosteus, Ag., Homosteus and Heteros- tions of each, and figures of all their separate 
teus of Asmus, and Chelyophorus, Ag. The Aste- parts, which are of very great value to the palae- 
rolepis, however, is not the Asterolepis of Hugh ontologist ; while his laborious attempt to unravel 
Miller. For the latter, Asmus's name Homosteus the complexities of the synonymy of these Fishes 
has the priority, according to Pander; while the is worthy of all praise. 
Pterichthys of Agassiz is that which was first 
