652 * 
POSTSCRIPT. 
intervals, throughout this micaceous sandstone, which forms a striking escarpment in this country of 
broad undulations 1 . 
We have next to express our regret, that owing to some accident in its transmission, we did not 
receive a memoir by Major Ozersky 2 , which gives a very clear and faithful description of the detailed 
succession of the strata that constitute the Silurian group of north-western Esthonia. After a very good 
account of the physical features of that tract, he describes a number of natural sections to the west of 
Reval, both on the coast and in the interior, as well as in the Isle of Dago 3 , and he divides the Silurian 
rocks into three members. The Ungulite sandstone there forms (as, indeed, Eichwald and others have 
observed) the base of the cliffs, which in ascending order consist of inferior grit, bituminous schist and 
greenish sandstone. This lowest member is followed by chloritic limestone, capped by a band of sand- 
stone and surmounted by a considerable thickness of limestone to which the author applies the term 
“ Fliessen-kalkstein,” dividing it into lower and upper beds. The third and uppermost division (also 
calcareous) is separated by him into a coarse-grained crystalline limestone beneath, and a compact though 
occasionally sandy limestone above, which constitutes the highest stratum he observed. Besides the 
Obolus or Ungulite, the lowest of these divisions contains the coral Gorgonia flabelliformis (Eichw.), and 
its upper beds the Sqihonotreta verrucosa (nob.) ( Terebratula , Eichw.). The middle group is (as described 
by us near St. Petersburg 4 ) the great storehouse of organic remains, and in the districts which he illus- 
trates Major Ozersky shows that it is more expanded than in any tract we have personally examined, 
whilst the fossils are those which we have enumerated and described. The upper group of this author is 
precisely that band which we have described near Shavli, Meshkovitza, Oberpahlen, &c., and which, as 
we have indicated, gradually disappears with the eastward range of the Silurian rocks ; for it contains 
our Pentamerus borealis ( Gypidia , Eichw.), and also several corals. 
In expressing our obligations to Major Ozersky for his lucid memoir, in which hedevelopes the litholo- 
gical features of each substratum with a precision worthy of so good a mineralogist as himself, we are 
however at variance with his concluding comparisons, wherein he endeavours to find exact parallels for 
each of his lithological subdivisions in the English detailed order of the Silurian rocks, as seen in certain 
typical British tracts. His upper continental stratum is thus considered by him to be the representative 
of the Ludlow rocks ; whereas in our estimate there is not a vestige of that formation in any portion of 
the mainland of the Russian Baltic provinces ; though it has a distinct existence with many characteristic 
fossils in the Isle of Oesel as determined by M. Pander (p. 35). The superior portion of the uppermost 
group of Major Ozersky may, indeed, where loaded with such corals as the Catenipora escharoides and Favo- 
sites Gothlandica, be assimilated to the Wenlock limestone; but the lowest bed of this calcareous mass, 
which is charged with Pentamerus borealis (closely akin to P. oblongus ), is clearly on the same level as 
the Horderley and Woolhope limestone of England, a point which we have indeed completely explained 
as respects Scandinavia, Russia and North America (pp. 5*, 12*. 34*). This Pentamerus bed forms so 
1 We made an excursion to this neighbourhood with M. Worth and Professor Kutorga, who had previously 
observed the chief relations here alluded to. 
2 See the volume of the Imperial Mineralogical Society of St. Petersburg, 1844. 
3 At p. 35 we have considered Dago as Upper Silurian, and, in fact, the Wenlock or Dudley corals are there 
abundant in its uppermost stratum ; but this isle contains the Pentamerus borealis and other fossils which pertain to 
the Lower Silurian strata, none of which are seen in Oesel. 
4 In addition to the proofs we have already adduced of the limestones of St. Petersburg being of Lower Silu- 
rian age, we beg to mention that our friend M. Volborth, who has so assiduously collected the fossils of this rock 
and described some of its Crinoidea, has detected in it the same Agnostus (Battus) which so distinguishes true Lower 
Silurian rocks at Kinnekulle and other places in Sweden and Norway. 
