POSTSCRIPT. 
652 ** 
clear a horizon in separating the Lower and Upper Silurian rocks over all parts of the globe where the)' 
exist, that so long as the original English classification he appealed to, no sort of doubt can be entertained, 
that every layer beneath it must be grouped with the Lower Silurian, as represented in our table attached 
to the Map, PI. VI. ; and it is therefore quite impossible to admit, that the chief limestones of Esthonia, 
which underlie that Pentamerus rock, can be compared with the Wenlock limestone. But in differing 
from Major Ozersky as to his comparisons of Russian deposits with those English formations with which 
we are necessarily well acquainted, we have specially to thank him for his excellent details of local suc- 
cession, and for pointing out other phenomena of some importance. One of these is the presence of a 
coarse conglomerate of fragments of crystalline rocks (our Azoic) in the Ungulite sandstones, thereby 
proving, that even in Russia the Lower Silurian strata have been constructed out of rocks antecedently 
crystalline, just as we have proved to have been the case in Scandinavia. Another of these phenomena 
(confirming our anticipations and of great value in sustaining our views derived from other localities, see 
pp. 328, 524, 539) is the existence of raised sea beaches containing remains of species of shells still 
living in the adjacent Baltic ; such as Cardium edule, Mytilus edulis, and Tellina Baltica ; which fact, com- 
bined with the evidences afforded by banks of gravel, sand and blocks, clearly points to a comparatively 
recent elevation of Esthonia, and hence of all the flat regions of Russia. The author further offers proofs 
of the polish and striation of the denuded limestones — appearances referred by him to the action of 
floating ice. Being for a moment on a subject which we have handled at some length in the preceding 
pages, wc may observe that during our present stay at St. Petersburg we have observed the phenomena 
on the surface of the yellow Silurian limestone south of Gatchina before alluded to, where it was first 
noticed by M. Worth and Professor Kutorga. It is also worthy of a comment, that in the neighbourhood 
of Gatchina, where the striation and polish are seen, there are no accumulations of fine gravel or loose 
drift ; huge, northern erratic blocks only occurring abundantly. In such instances, we willingly admit 
that the polish and striation may have been produced by the onward motion of ice-floes (carrying these 
blocks) which stranded in shallows and grated along the subjacent rocks. Such an action, however, we 
again maintain could never have been adequate to the uniform maceration, smoothing and grinding down 
(in the manner we have described) of all the northern faces of the crystalline rocks of Finland, Sweden, 
and of the myriads of isles of the Bothnian Gulf. 
We have next to acquaint our readers, that the Map, PI. VI., has received considerable improvement 
at its north-eastern extremity from the researches of the distinguished botanist Schrenk, who in the year 
1836, and previous to his arduous tour in South-Eastern Siberia and along the Chinese frontier 1 , gallantly 
faced the most inhospitable of all the Arabian tracts, and traversing the wilds of the Samoyedes to the 
Straits of Vaigatz, not only determined the physical geography and natural history of the region forming 
the end of the Arctic Ural, but also brought back collections sufficient to establish geological demarca- 
tions in a country which may not for a century be visited by any other man of science 2 3 . 
Whilst on the subject of new discoveries in the boreal tracts of Russia, we may mention, that the 
enterprising traveller Professor Middendorf of Kief has brought back with him from the shores of the 
Arctic Sea (between the rivers Obe and Lena), numerous fossil shells which on inspection we had no 
hesitation in identifying with those Oxfordian types with which we had become familiar in many parts 
of European Russia. Associated with numerous Belemnites and true Ammonites, we detected also those 
1 See last Anniversary Discourse of Mr. Murchison as President of the Royal Geographical Society. Journal 
of the Royal Geographical Society, vol. 15, p. ci. 
3 The chief geological data resulting from an examination of M. Schrenk’s fossils, will be given in the forthcoming 
work of our friend and coadjutor. Count Keyserling, on the Timan, Petchora, etc., which, as we have previously 
said, forms a natural sequel to these volumes. 
