Chap. XIV.] 
SILUKIAN ROCKS OF EUSSIA. 
355 
two groups are there often exhibited, as in the preceding sections, in such 
frequent undulations as to constitute one united mass of very small thick- 
ness, all the strata of which have a community of aspect, and maintain a 
perfect parallelism to each other. 
The identity which I formerly established * between the chief limestones 
of Gothland (together with certain isles in the Bay of Christiania) and 
those of Wenlock and Dudley was proved by the great number of the 
fossils eommon to Scandinavia and Britain, and is now well known to all 
geologists and collectors. 
Silurian Bocks of Russia. — Following these ancient deposits into the 
Baltic Provinces of Eussia, and beginning our examination of them in the 
environs of St. Petersburg, where their lowest beds are exposed, we find 
that the hard crystalline rocks of Scandinavia and of Finland have sub- 
sided beneath the sea-level, and that we can nowhere observe that junc- 
tion, so clearly observed in Norway and Sweden, between the lowest 
Silurian rock and the masses which were formed before it. 
Ranging from the banks of the River Neva at the Imperial metropolis to the 
cliffs west of Narva, the lowest visible strata are composed of bluish or greenish 
shale (the ' blue clay ' of Russian geologists), though, in sinking the piles for 
the support of the new granite bridge at St. Petersburg, and in other subter- 
ranean works, courses of incoherent sand have also been met with in it. This 
clay, although as soft as that of Tertiary age in and around London, and so 
plastic as to be used even by sculptors for modelling, is clearly of the same 
age as some of the oldest strata described in Sweden and Norway, or as the 
much harder and more crystalline lowest Silurian slates of Wales; so en- 
tirely have these venerable Russian strata been exempted from the influence of 
change. 
The lower clay or shale is followed upwards by sandy beds in parts sufficiently 
coherent, particularly when cemented by oxide of iron or a little calcareous 
matter, to form a sandstone, occasionally a calcareous grit, on which the Castle of 
Narva stands. On the banks of the Rivers Ishora, Tosna, and Siass, tributaries 
of the Neva, these sandy strata are interlaminated by thin courses of shale, ap- 
proaching to impure fuller's earth, the sandier parts of which are intermixed 
with green grains, and occasionally contain small concretions. In these layers 
Pander found several of his microscopic Conodonts ; but the organic bodies 
which specially characterize this band are Obolus Apollinis, Eichw. (the 
Ungulite of Pander), Orbicula (?) Buchii, and 0. (?) reversa, de Vera., and some 
rarer shells termed Siphonotreta and Acrotreta. Of these, however, the little 
horny Brachiopod the Obolus or Ungulite is so much more abundant than 
any other fossil as to have induced Pander to give to the rock the name of 
1 Ungulite-grit.' 
This Ungulite-grit is overlain by a course of dark-coloured schist, which con- 
tains Graptolites, and is often bituminous, particularly in Esthonia, where it has 
even been extracted for fuel. / 
It was in the green sands associated with the Ungulite-grit and bituminous 
shale, that the distinguished palaeontologist, the late Dr. Pander, discovered 
those minute bodies (of the size of pins/ heads and less) which he termed Co- 
* Quart. Journ. GeoK Soc. vol. iii. pp. 18 &c. 
