512 DRIFT AND ERRATICS NEAR ST. PETERSBURG. 
Standing as it does on the very northern edge of the Silurian band and in the 
lowest stratum of that formation, St. Petersburg and its environs is a favourable 
tract foi studying the distribution of the northern drift. 
In travelling to the north of that metropolis, hills chiefly composed of sand, derived from the wearing down and 
washing of the adjacent granitic region, are soon found to contain many blocks of northern origin, and these increase 
in quantity and magnitude, forming ridges and undulating hills, from which you pass to the edge of the crystalline 
nucleus of Finland. To the south of the capital the Lower Silurian clay has been to a great extent denuded, 
or covered merely with more recen. alluvial deposits. On this flat, granitic and northern blocks are com- 
paratively rare, though an occasional specimen of very great size has been detected in the marshes ; but no sooner 
is the plateau land on the south ascended (the framework of which consists of the Lower Silurian limestone), than 
vast quantities of these blocks, some rounded and others not much so, occur both in isolated patches and in 
“ trainees.” They are seen on all the elevations on both sides, and particularly to the south of the observatory of 
Pulkova, and on the tops and slopes of the ravines (into which they are occasionally rolled), whether on the sides 
of the brook Pulkovka or all along the low eminences which slope away to Peterhoff. The calcareous plateau 
to the south of Czarskoc-Celo and the sandy valley of Pavlosk, are for the most part void of them, the latter being 
absolutely filled with the sand derived from the breaking up of the ungulite sandstone ; but a vast and copious 
trainee is seen upon the southern slope of one of the hills, near the sources of the little river Slavenka. 
We particularly remarked that in this group of the Slavenka, the greater number 
of the blocks were by no means rounded ; many, indeed, are still quite angular 
and some subangular. Being accompanied to this spot by Dr. Worth, to whom, 
in former pages, we have so warmly expressed our obligations, that zealous mine- 
ralogist distinctly assured us, that there was not among these blocks (whether 
gneiss, granite, or greenstone, &c.) a single example which could not be paralleled 
with its parent rock in Finland. Here again, as in the Dorpat and Lithuanian 
tracts, we had a convincing proof, that the direction of the drift had been from 
north to south, quite independently of the Finnish blocks ; for the true Devonian 
rocks, which are here charged with ichthyolites, are surmounted by flag-like frag- 
ments of the Lower Silurian limestone, occasionally very large, which have been 
drifted from the adjacent plateau on the north 1 . 
1 We cannot give this passing account of the detritus near St Petersburg, without adverting to the 
more detailed description of it by Mr. Strangways (Trans. Geol. Soc., Old Series, vol. v. p. 392) 
Showing that the drift is often from thirty to forty feet thick, and sometimes occupies entire hills, he 
states that it is made up both of crystalline rocks that have been transported from Finland on the north 
(referring many of them to their native quarries) and of the debris of the strata in situ. In regard to the 
latter, he mentions how the wide spread of sands in some tracts, particularly to the north of the Neva and 
the environs of Peterhoff and Pavlovsk, has been occasioned by the breaking up of what he calls the “ inter- 
mediate sandstone” (our Ungulite sandstone), and how the limestone, or “pleta,” is usually covered with 
light brown earth. We were also struck, as well as Mr. Strangways, with the appearance of thick 
masses of very finely laminated clay on the road from St. Petersburg to Strelna, and in which there occur 
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