108° : 
these gentlemen in the South of Russia are explained. « ‘These let- 
ters communicate important additions to the results already offered 
to the Geological Society, particularly in regard to the extension 
and development of the carboniferous system. The geological map 
which has been prepared by their labours, and from those of other 
Russian authorities, agrees with that of Mr. Murchison and M. de 
Verneuil, exhibited to the Society, in the fundamental classification 
of the rocks which occupy the northern and central governments of 
Russia, and in the lines of demarcation between the Silurian, Devo- 
nian or Old Red, Carboniferous, Newer Red, and Oolitic Systems ; 
but it is copiously enlarged, by showing the extension of the car- 
boniferous system over a very wide area, ranging from near Witepsk, 
by the south of Tula and Kaluga, to the S.E. of Cazan. A vast 
spread of chalk and tertiary deposits directly overlies these carbo- 
niferous limestones, which rise again from beneath these younger 
formations in the great carbonaceous tract of the Donetz, the 
southern edge of which consists of the granitic steppe.» A sec- 
tion made by Count Keyserling and Professor Blasius to the south 
of Kaluga, indicates a succession from what these naturalists be- 
lieve to be the lower beds of the carboniferous limestone, contain- 
ing Spirifer Mosquensis, into superior strata of sand and shale 
with coal, subordinate to bands of limestone containing the Pro- 
ductus hemisphericus, the coal beg associated with much red earth, 
and overlaid by the upper carboniferous limestone. They also 
express their belief that the millstone grits which have been alluded 
to near Moscow must be considered of tertiary age, as similar beds 
overlie true chalk. , 
_- Mr. Murchison takes this opportunity, in the name of his feitonms 
M. de Verneuil and himself, of recording his sense of the value of 
the additional data which are due to the labours of Baron de Mey- 
endorf and his associates, and trusts that after an exploration of the 
flanks of the Ural, and other tracts near Orenburg and in the South, 
all the chief facts will have been obtained for the construction of a 
general geological map of Russia in Europe. 
Count Keyserling, who has traced the shales with. Ammonites 
near Ust-Sisolsk (N. Lat. 61°, E. Long. 51°*), has indeed contri- 
buted most powerfully to these results, both by his patient obser- 
vation, sound knowledge of natural history, and by his barometrical 
admeasurement of heights,—a point of great geological importance 
in those central parts of the country where the strata are not de- 
ranged. . By one of his observations, it appears, that the younger 
pleiocene deposits on the Dwina, which he detected in company 
with M. de Verneuil and Mr. Murchison, are about 150 feet above 
the White Sea. Count Keyserling, now at St. Peterburgh, will 
accompany the authors in their journey to the Ural Mountains this 
summer.—March 26. oat 
* Similar Jurassic beds had been previously observed by M. Strajeske 
in the N. Ural, Lat. 64° north, and their fossils are described by M. Leopold 
de Buch in his recent work, ‘ Beitrage zur Destibarasiai der Ceblrestfonne: 
tionen-in Russ-land.’ 
