
688 STRATIGRAPHICAL GEOLOGY. [Boox Vi. 
crumpling, invasion of eruptive masses or other disturbance. In their 
general character and order of succession these Scandinavian rocks ~ 
present many points of resemblance to the altered Silurian series of the 
Highlands of Scotland already described (p. 583). Tornebohm divides 
them into two series—the Seve group, composed of a set of quartzites, 
and crystalline schists covered by the Kéli group, in which mica-schists 
and clay-slates are the chief rocks. The latter may be metamorphosed - 
shales, and it is remarkable that, as in Scotland, the lower parts of the 
group are generally the less altered.) 
In Russia Silurian rocks must occupy the whole vast breadth of 
territory between the Baltic and the flanks of the Ural Mountains, 
beyond which they spread eastward into Asia. ‘Throughout most of this 
extensive area they lie in horizontal undisturbed beds, covered over and — 
concealed from view by later formations. Along the flanks of the Urals 
they have been upheaved, and placed on end or at a high angle against 
the central portions of that chain, and have been partially metamorphosed 
into chlorite-schist, mica-schist, quartz-rock, and other crystalline masses. 
But along the southern margin of the Gulf of Finland they appear at the 
surface as soft clays, sands, and unaltered strata, which, so far as their 
lithological characters go, might be supposed to be of late Tertiary date, 
so little have they been changed during the enormous lapse of ages since ~ 
Lower Paleozoic time. The great plains between the Ural chain on the 
east and the rising grounds of Germany on the south-west have thus 
from a remote geological antiquity been exempted from the terrestrial 
corrugations which have affected so much of the rest of Europe. They — 
have been alternately, but gently, depressed as a sea-floor, and elevated 
into steppes or plains. The following subdivisions have been established 
by F. Schmidt among the Silurian rocks of north-west Russia : ? 
I. Upper Silurian. 
» 3 (Sandy variable limestone, with marly layers passing into sandstone 
(Beyrichia tuberculata, Grammysia cingulata, Chonetes striatella and 
numerous fish remains, Onchus, &.). 
: {cho Oesel Group, yellow marly and sometimes dolomitic strata (Rhyn- 
Tile 
ston 
chonella Wilsoni, Chonetes striatella, Platyschisma helicites, Eurypterus 
remipes, and fish remains, &c.). 
Lower Oesel group, dolomite, with marl and coral limestone below (Propora 
tubulata, Halysites distans, Beyrichia Kledeni, Enerinurus punctatus, 
Proétus concinnus, Meristella tumida, Spirifera crispa, Leptena transver- 
salis, Huomphalus funatus, Orthoceras annulatum, &e.). 
Pentamerus band, with P. ehstonus (oblongus), Alveolites Labechet, Belle- 
rophon dilatatus, Bronteus signatus (laticauda). 
Compact limestone and dolomite with siliceous nodules (Heliolites inter- 
stinctus, Ptilodictya scalpellum, Strophomena pecten, Orthis hybrida, 
Pentamerus linguifer, Leperditia marginata). 
Pentamerus band, limestone, and dolomite, with Pentamerus borealis, &c. 
Il. Lower Silurian. 
Borkholm limestones and marls (Halysites labyrinthica, Heliolites mega- . 
stoma, Syringophyllum, organum, Lichas margaritifer, Plewrorhynchus 
dipterus, Orthoceras calamiteum, &c.). 
Lyckholm, yellow or grey compact limestone and marls (Orthis flabellulum, 
O. Actonix, O. insularis, &e.). 
Wesenbery limestone and marl (Orthis testudinaria, Enerinurus multi- 
segmentatus, Lichas Kichwaldi, &¢.). 
Lud- 
low 
Llandovery. Wenlock. 
Caradoc. 
' A. BE. Toérnebohm, Bihang till K. Svenska Vet. Akad. Handl. i. No, 12, 18738. 
2 Untersuchungen iiber die Silurische Formation von Ehstland, Nord Livland und 
Oesel, published in Archiv fir die Naturkunde Liv, Ehst. und Kurlands, Dorpat, 1858. 
