ERRATICS OF ESTHONIA AND ST. PETERSBURG. 
511 
which occupies the coast, the detritus consists of rolled and rounded fragments 
chiefly of Silurian limestone, here and there capped by a great granitic block, — a 
tract most joyfully reached by those who, travelling as we did in the early spring, 
just after the melting of the snow, had with such difficulty ploughed through the 
muddy, marly and sandy detritus of the western district. We shall afterwards 
enlarge on a feature which here struck us forcibly, viz. that the principal mass of 
the detritus of each district is of local origin, and very clearly bespeaks the nature 
of the subjacent formation ; whilst the great northern drift is perfectly independent 
of such subsoil, and has been distributed in zones, or “ trainees,” which traverse 
the Silurian, Devonian, and Carboniferous regions. 
On reaching the cliffs of Lower Silurian limestone, which stand out against 
the sea of the Gulf of Finland, we found their surface completely denuded of all 
local drift (their calcareous debris having been swept to the south). Without any 
accompaniments of smaller gravel, or rounded stones or clay, the hard limestone 
flags are there at once covered with blocks large and small, nearly all angular or 
subangular, which are spread about in little groups or single masses, as represented 
in this woodcut. 
Gulf of Finland. 
67 . 
Northern granite blocks. 
Orthoceratic limestone. 
Ungulite grit. 
Bituminous schist. 
Shale obscured by fallen blocks. 
Here then are blocks, every one of which may be paralleled with the granitic, 
porphyritic, or gneiss rocks of Finland, and which have clearly been transported 
without rubbing or friction ; for they are not rounded or worn down by any attri- 
tion, and are unaccompanied by the rounded boulders, clay, or sand, which indi- 
cate a drift by water alone. They must therefore have been lodged or deposited 
on these cliffs (150 feet or more above the adjacent Baltic) by some cause inde- 
pendent of pure aqueous action. To the consideration of this point we shall 
hereafter return 
Let us now continue to make the general transverse section of all the northern 
detritus which occurs along the southern frontier of the crystalline rocks of Finland 
and Russian Lapland. 
3 u 2 
