27 
UNGULITE GRIT OF ST. PETERSBURGH. 
which intersect the line of hilly grounds extending from Czarskoe-celo to Duderhof, 
where it is seen to crop out from beneath low promontories of superjacent sandstone 
and limestone. The general order of the strata from Petersburgh on the north to 
the hills of Czarskoe-celo on the south is sufficiently expressed in this woodcut. 
3*. 
St. Petersburgh. Hills of Czarskoe-cclo . 
a. Blue shale. b, Ungulite grit and bituminous schist. c. Orthoceratite limestone. 
The backwardness of the vegetation on the argillaceous tract near St. Peters- 
burgh may with great reason be attributed to the influence of a subsoil, so retentive 
of moisture, wherever its surface is not ameliorated by a cover of northern drift, 
the sandy portions of which afford, on the contrary, a good drainage and a healthy 
residence. Though differing widely in age, the oldest Silurian clay of St. Peters- 
burgh (the equivalent of the lowest Silurian slates of other countries) and the 
tertiary clay of London produce precisely similar effects. The English florist, 
farmer, and valetudinarian, have long since learnt to avoid the heavy and cold 
clay, even where it rises into hills around the English metropolis, and to prefer 
the absorbent gravel and sand with which fortunately in so many parts the clay is 
overspread, and under which its noxious qualities are buried. A similar distinction 
is quite as apparent between the district of the undulating sandy hills to the north 
of the Neva, and at Pavlosk and Peterhof, and the lower argillaceous tracts around 
St. Petersburgh. 
2. Ungulite Grit . — This sandstone, first described as “ intermediate sandstone ” 
by Strangways, and since named Ungulite Grit by Pander from the peculiar fossil 
bivalve which it contains, is seen to overlie and pass down into the shale, in the 
ravines and banks of the brooks on the south of St. Petersburgh. Its lowest layers 
frequently consist of whitish sandstone, composed of grains of sand cemented by 
siliceous matter, and in rarer instances assuming the structure of a hard calcareo- 
siliceous grit. In the “ chatoyant” lustre of their newly-fractured surfaces, certain 
portions of the rock, seen in the bed of the Pulkovka brook near Petersburgh, very 
closely resemble the slightly calcareous grits of the tertiary and secondary forma- 
tions, such as the “ grls de Fontainebleau,” the concretions of the Hastings sand- 
stone of England, or the calcareous grits of Brora, and, like these rocks, such parts 
of the Russian sandstone effervesce slowly with acids. 
