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black, and red mud, or sand which occupied the bottom of seas in 
former epochs, it seems as difficult to decide from general observa- 
tions on the maximum thickness of any great deposit, as it would 
be to insist on the utmost depth of the ocean without the survey of 
the hydrographer. ‘The borer and the field engineer must therefore 
combine to enable us to speak with precision on the vertical dimen- 
sions of strata. 
RUSSIAN AND NORTHERN SCHOOL. 
Not having yet personally visited Sweden, Norway, and Den- 
mark, Iam not prepared to say what progress our science has re- 
cently made in these states, but | may remark, that the beautiful map 
of Norway by Keilhau has scarcely received the attention which it 
merits; and we may be sure that the countries of so good geolo- 
gists as himself and our associate Forchhammer, cannot be lagging 
behind in the general onward movement. 
In regard, however, to Russia, I am enabled to speak with some 
confidence, after the two visits which I have paid to that country. 
Gratified as we were, not only by the most hospitable reception, but 
also the kind assistance afforded us by every Russian, from the Em- 
peror to his humblest subject, it was a real source of delight to my 
associates and myself in our first visit to trace throughout the north- 
ern regions of that vast empire, the same paleozoic divisions which 
have been proposed as types in the British Isles. During the last 
summer we extended our researches to the distant Ural, the Siberian 
plains, and the steppes of the south; and afterwards terminated the 
whole of these observations by a general transverse section from the 
sea of Azof to the Baltic. Although we carried with us into Russia, 
what may be called the geological key of that great country, by which 
the chief subdivisions and relations of these rock masses have been 
established, let me say that Russia herself contains naturalists and 
geologists who would rank high in any land. In paleontology, 
Eichwald and Pander have already largely contributed to our know- 
ledge ; the first, by numerous local works, and recently by his illus- 
trations of the Silurian strata in the Baltic provinces of Russia; the 
latter, by his very original researches into the fossils of the same 
strata, the lithological characters and detailed relations of which 
were first given by our own Strangways. Professor Asmus of Dorpat 
is about to enrich us, as I have already stated, with a most curious 
and elaborate work on the fishes of the Old Red or Devonian system. 
The great steps, however, which Russia is now making in field 
geology and stratigraphical arrangement, are owing to the clear and 
well-defined view of this subject which has recently been adopted 
by the Imperial School of Mines at the suggestion of the energetic 
chief of their staff, General Tcheffkine, who, under the orders of 
the enlightened Minister, Count Cancrine, has taken the surest 
means of advancing practical geology, and of rendering many 
officers of his corps well acquainted with our subject; not only by 
adopting the suggestions of those qualified to judge respecting the 
formation of geological maps, but by so increasing the fossil eollec- 
