: 407 
action which had once been so dominant in these northern tracts; 
and they were unable to account for them satisfactorily, until they 
detected the results of modern action of river ice, which completely 
explained the lacustrine case. 
About 80 miles above Archangel they met with a ridge of large 
angular blocks of white limestone piled up between ‘the’ road on 
‘ which they travelled and the river edge, and about 20 or 30 feet 
above the stream. Having ascertained that this great river was pe- 
riodically subject to occasional extraordinary rises in the spring, and | 
that on those occasions it bursts and throws up upon its banks blocks 
of ice to heights of 20 or 30 feet above its ordinary level, they had 
at once a solution of the phenomenon; for the blocks of white lime- 
stone had evidently formed parts of the subjacent strata, which, 
projecting into the mud and water on the edge of the Dwina, had 
been first entangled in ice, and rent off at their natural joints upon 
the expansion of the ice by which they were upheaved into their 
present position, taking their present irregular talus shape when the 
ice melted away from them. Believing, therefore, that the angular 
ledges on the lake of Onega were similarly formed, the authors see 
in them the proofs of the lakes of Northern Russia having formerly 
stood at much higher levels, from which the waters, they suppose, 
have been let off by successive elevations of the land; and they fur- 
ther think, that the diminution of shallow lakes, and the conversion 
of marshes into land within the historic period in Northern Russia, 
strongly corroborate the rise of this portion of the earth. 
. Conclusion.—In recapitulating the chief point of the first and prac- 
* tical part of their Memoir, wherein they establish, they trust, on a 
sound. basis, the general classification of the Paleozoic Rocks of 
Russia in Europe, the authors remark, that the fact of some of the 
deposits of such high antiquity being found.to stretch in horizontal 
and almost unbroken sheets over spaces of a thousand miles in length, 
in a very slightly solidified or lapidified state, is the more interesting 
when coupled with the absence, throughout the same regions, of all 
plutonic or igneous rocks. ‘This phenomenon must, it is conceived, 
exercise considerable influence upon geological theory, it being now 
apparent, that the lithological nature of the most ancient subsoil of 
Russia in Europe is such as to compel geologists to reject the con- 
clusion, that in proportion to their antiquity the strata have been 
hardened or crystallized by any general radiation of central heat; 
for in these wide tracts such crystalline and hardened state is clearly 
seen to be purely metamorphic, and dependent exclusively on the 
vicinity of rocks of igneous protrusion, in receding. from which to 
the South all the strata described are at once found in their normal 
soft condition. o aor 
In taking leave of the Society, the authors explained some of the 
chief objects of their journey to the Ural Mountains, Orenburg, &c., 
on which they were about to proceed. 
Note.—After these sheets were sent to press, Mr. Murchison re- 
ceived letters from his friends and fellow-travellers, the Baron A. de 
Meyendorf and Count A. Keyserling, in which the researches of 
