NORTHERN TRANSVERSE ERUPTIONS AND DISLOCATIONS. 
23* 
into indurated, siliceous masses, passing here and there almost into granular quartz 
lock. Such phenomena are well displayed in the tracts near to and to the north of 
Petrozavodsk and the Lake Onega, where the hills rise to heights of 500 and 600 
feet above the sea, and where the long ridges of greenstone, just alluded to, prevail. 
The crystalline limestones, which we saw, betrayed few recognizable forms of or- 
ganic remains ; but the flat-bedded, quartzose grits are occasionally of a reddish 
colour, exhibit rippled surfaces, fucoid-like markings, imbedded fragments of older 
rocks, and many other indications of their original condition. They have also 
varied and sometimes opposite dips ; but this condition, as well as their structure, 
changes instantly upon quitting the region where intrusive rocks are visible. In 
travelling from north to south you pass suddenly from slates to shale and mud, 
and from inclined, hard quartzose rocks, to horizontal soft sandstones and marls 
with organic remains. In this respect, indeed, the phenomena of the northern 
region are similar to those of many other parts of the earth’s surface where intru- 
sive rocks have risen through sedimentary deposits ; but over what exact area this 
metamorphism of the original strata has been carried, we are not now prepared to 
show. We have now simply to state, that all along this Lappish frontier, in the 
governments of Olonetz and Archangel, nature has placed a bar to a correct 
examination of the sedimentary strata, in descending order, beneath those of De- 
vonian age. The thorough examination, however, of this great band of Silurian 
rocks, more or less metamorphic, which lies between the purely crystalline or azoic 
north and the wholly unaltered Devonian and carboniferous deposits 
the south, well merit the special attention of the geologist, mineralogist, and 
c lemical philosopher ; for the scale on which these operations of change have been 
conducted is gigantic. Our present acquaintance with the phsenomena is, however, 
sufficient to convince us, that here, as in other countries, the consolidation, rupture, 
and alteration, of large portions of the earth’s crust, have been effected by the 
agency and eruption of igneous and gaseous matter. In our subsequent account 
°f the Ural Mountains we shall develope our views on this subject; and in the 
meantime terminate this sketch of the northern frontier with a few reflections on 
tbe line of separation between the more ancient crystalline rocks and the sedimen- 
tary strata of the central regions of Russia. 
Transverse Dislocations along the Northern Paleozoic Frontier . — By casting his eve 
over our Map the reader will perceive, that the masses of metamorphosed pakeozoic 
rocks on the Lake Onega, to which we have been adverting, form part of a long 
