101 



900 feet above the sea ; and it is very remarkable by being charged in 

 miany localities with ichthyolites, several species of which, hitherto 

 considered peculiar to the Scottish Old Red Sandstone, are found 

 associated with MoUusks, perfectly similar as a group, and often 

 specifically the same, as those of the limestones of South Devon, 

 the Boulonnais and the Eifel. The discovery of the intermixture 

 of Scottish Old Red Sandstone fishes and true Devonian shells in the 

 same strata, was, you may believe, one of the most gratifying results 

 of the recent explorations in Russia, as being confirmatory of the 

 views of Professor Sedgwick, Mr. Lonsdale and myself respecting 

 the divisions and equivalents of that member of the Palaeozoic Rocks. 

 In some parts of Russia, the Devonian rocks are red sandstones and 

 marls ; but in an extensive central tract, where they rise into a dome 

 which separates the northern from the southern basin of the em- 

 pire, they are composed of yellow sandy marls and limestones, which 

 lithologically might be mistaken for the magnesian limestone beds of 

 our northern counties : — so inapplicable are mineralogical terms as 

 marks of geological epochs. 



In the vastness of their undisturbed and nearly horizontal extent, 

 these strata afford us most instructive proofs of the intimate con- 

 nection between the stony condition of the rocks and the imbedded 

 fossils ; for, when the calcareous matter is present; various moUusks 

 are associated with some fishes, whilst in those tracts where the lime- 

 stones disappear and the beds have the characters of the Old Red 

 Sandstone of Scotland, fishes only can be detected : thus presenting a 

 remarkable analogy between the distribution of this very ancient 

 fauna and that of existing nature ; the present great receptacles of 

 fishes being deep sandy bottoms, whilst shelly creatures congregate 

 towards the shores where calcareous springs attract them. I shall 

 elsewhere allude to the fishes of this deposit when speaking of the 

 researches of Professor Agassiz. 



Carboniferous Rocks. — TheCai'boniferous deposits, which succeed, 

 cover an area as broad as that of the Devonian or Old Red rocks ; 

 and they are throughout clearly distinguished by a decidedly di- 

 stinct type of animal life, presenting in some families an extraordi- 

 nary number of species absolutely undistinguishable from those of 

 our own country published in the works of Sowerby and Phil- 

 lips. This system is eminently calcareous, and exhibits a vast 

 marine succession, in which the fossils of the Mountain Limestone 

 prevail, whilst in no part of the empire is there a trace of the over- 

 lying deposits, with which we are familiar under the term of " coal- 

 measures." Coal, however, does occur at intervals, both underlying 

 the carboniferous limestone, as in Berwickshire, and alternating 

 with its central and upper members, as in Northumberland, and the 

 carboniferous valleys of our lake country. 



Of the latter, the extensive tracts in the south of Russia, occupying 

 from 10,000 to 11,000 square miles, and usually known as the 

 country of the Donetz, offer a very striking illustration ; containing 

 in one district as many as seven good seams of coal, subordinate 

 to sandstone, shales and limestones, very analogous to those rocks 



