23 
INTRUSIVE ROCKS AND ALTERED PALAEOZOIC STRATA. 
seek for detail to a memoir by M. Engelmann 1 , we shall not further describe their 
lithological character than to say, that these eruptive rocks chiefly consist of 
greenstones, graduating through coarse and fine-grained varieties into syenite and 
porphyry, with hornblende slate, &c. 
The little isle of Solimen, north of Petrozavodsk, is so far an exception, that it 
is composed of a very remarkable trap-breccia or greenstone conglomerate, the 
“ Solimenski-kamen ” of the Russians. This rock, which extends over a con- 
siderable space, is composed of angular fragments of apparently altered slate or 
Lydian stone, imbedded in a trappean matrix, with very minute felspathic veins. 
These eruptive masses, advancing from the crystalline region of Russian Lap- 
land, trend in long bands from N.N.W. to S.S.E., which are parallel to the num- 
berless lakes of this northern country (see Map), the latter occupying depressions 
between promontories of greenstone. One of these promontories, for example, 
runs parallel to the western banks of the Lake Onega, where it rises through hard 
quartzose sandstones, into prominent wooded hills, 400 or 500 feet above the 
water. The most southern tongue of these trappean rocks is composed of horn- 
blende and compact felspar, and from a greenstone passes into syenite and syenitic 
greenstone, which form a picturesque headland on the left bank of the Svir, where 
that clear stream issues from the Lake Onega 2 * 4 . 
Although, strictly speaking, we ought not to speak of altered rocks before we 
have described the strata in their normal or unaltered condition, we shall render 
our view of the general relations of the masses more clear, by at once saying a few 
words upon this point. Whenever the quantity of overlying detritus permits their 
northern edges to be examined, the unaltered sedimentary rocks we are about to 
describe, are separated from the great granitic or azoic region of the north by a 
zone of considerable width, in which the shales have been converted into coarse 
slates or Lydian stone, the limestones more or less into marble, and the sandstones 
1 Annuaire du Journal des Mines de Russie, annee 1838, p. 50, “ Sur la composition geologique de 
1’arrondissement minier d’Olonetz : ” in which the author gives an elaborate description of the Soli- 
menski-rock. 
4 Colonel Armstrong, the Director of the Imperial Iron Foundry at Petrozavodsk has prepared a 
mineralogical map of this neighbourhood. We were indebted to that officer, not only for a most hospi- 
table reception, but also for much information, in regard to the range of the crystalline rocks and the 
alluvial phenomena, including the deposits in lakes which supply the foundries with iron ore. (See ac- 
count of the superficial phenomena of this tract, pp. 514, 567.) 
