Huti-—On the Geological Age of the North Atlantic Ocean. 311 
The Lower Silurian beds occupy large tracts of the Scandinavian promontory, 
resting unconformably on the Archzan metamorphic beds, or sometimes on repre- 
sentatives of the Cambrian deposits. From their position along the shores of the 
Gulf of Finland and the Baltic, on the north and west of European Russia,* and 
again along the line of the Oural Mountains, it may be inferred that they underlie 
the whole of Central Russia. Here, however, the formation has become largely 
calcareous, and reduced in thickness to one-tenth of its volume in the British Isles. 
The formation occupies portions of the north of France, and has been proved by 
borings to underlie the Cretaceous strata of northern Belgium, as shown by Pro- 
fessor Gosselet. The great extent of beds of this age in Spain has been long 
known by the researches of both Spanish and other continental geologists. Very 
recently the work of M. Charles Barrois has put us in possession of the most 
recent results as regards the older rocks of the north of that country. From his 
observations it would appear that the three divisions of the Lower Silurian series 
attain a thickness of about 600 metres, or 2000 feet, at Cape Vidrias;+ but in 
other districts the thickness is undoubtedly much greater. Comparing the thick- 
ness of the Silurian strata in Northern Russia, Scandinavia, and the British Isles, 
we cannot but be struck by their great vertical expansion in the direction of 
the latter country (from 1500 or 2000 feet in Russia to 20,000 or 25,000 in 
Britain)—a fact which Murchison has more than once directed attention to,t but 
without (as far as I can see) drawing the inference which, I think, is fairly deducible 
regarding the position of the originating land of the period. 
In the north of France the Lower Silurian rocks attain to great vertical dimen- 
sions, probably not fallmg short of those in Wales and Ireland. The section of 
these rocks in the Department of the Sarthe, from Sillé le Guillaume to Chemiré, as 
given by MM. Triger and de Verneuil, shows a thickness of these beds amounting 
to nearly 20,000 feet. They consist, with one slight exception, of sedimentary 
strata (slates, sandstones, and conglomerates), surmounted by those of Devonian age. 
From a general comparison of the development of these strata in various 
parts of the European and British area, there is evidently a great expansion in a 
westerly direction, indicating the position of the land from which the sediment 
was derived. This indication is also rendered more striking if we compare the 
composition of the strata of the west with those of the east. For along the bor- 
ders of Russia and the Baltic provinces the strata consists largely of limestones, 
which, as we know, are but very sparingly represented amongst the Lower Silurian 
strata of Britain and France, and point to the Russian area as having been some- 
what remote from land, while the waters which overspread it were generally free 
* Prof. F. Schmidt, ‘Quart. Journ. Geol. Soe.,” vol. xxxviii. p. 515. 
| « Recherches sur les Terrain anciens des Asturias et de la Galici,” p. 451. 
“ Siluria,”’ 4th edit., ch. xiv. 
Lm 
** Bull. Soc. Geol. Fr.,”’ vol. vii. ser. u., quoted by Murchison, “ Siluria,” 4th edit., p. 408. 
