356 
SILTJRIA. 
[Chap. XIV. 
nodonts, and which were referred by him to Fishes. If this suggestion had been 
borne out by inquiry, my broad generalization as to the first appearance of ver- 
tebrata, and to which I attach great importance, would have been set aside ; 
but the able microscopists Carpenter, Quekett, and Harley, as well as Barrande 
and others, have rejected the idea of their being parts of Fishes, referring them 
to Crustacea and other low animals. Professor Owen, having favoured me with 
a similar opinion, declared that they present ' the most analogy with the spines, 
hooklets, or denticles of naked Mollusks and Annelides.' The detailed descrip- 
tion of them by Professor Owen is given in the Appendix (E), and thus the 
question is completely set at rest. 
A curious addition to our acquaintance with the minute fossils of the green 
sand of these Lower Silurian rocks of Russia was made by my eminent friend 
Dr. Ehrenberg, who discovered that many of the green grains consist of the sili- 
ceous casts of Foraminifera f. 
The chief or Orthoceratite limestone (the Pleta), which follows, is charac- 
terized at its base by sandy calcareous beds containing a profusion of those dark- 
green grains which are here and there apparent in the subjacent strata, and 
which have been supposed to be the debris of ancient augitic rocks of Finland 
(see 4 B,ussia-in-Europe,' p. 28*), but may, to some extent at least, have been 
derived from the silicated moulds of Foraminiferal shells. In lithological aspect, 
however, these lower calcareous beds usually so resemble the ' Craie chloritee ' of 
the French, or the green varieties of the Upper Greensand of England, that, 
when mineral characters alone guided geological classification, they were even 
supposed by Alexander Brongniart to belong to the Cretaceous system. That 
misapprehension, however, was long ago removed by the works of Pander and 
Strangways. Separated by wayboards of greenish-grey or reddish shale, these 
green calcareous beds are surmounted by the earthy, grey, flat-bedded limestone 
which, occupying the hills of Czarskoe Celo and Duderhof south of St. Peters- 
burg, ranges westward into Esthonia, and is the chief fossiliferous band of the 
Lower Silurian rocks. Conodonts have been found by Pander chiefly in the 
Lower Silurian Bocks in the Cliffs near Waiwara, Gulf of Bothnia. 
a. Lower shale, obscured by fallen fragments of rock and ice-borne Scandinavian 
blocks, b. Ungulite-grit. <?. Argillaceous schist, with Graptolites (Pbyllograpsus). 
d. Orthoceratite-limestone (covered by granite-blocks which were transported from 
Sweden during the Glacial Period : ' Russia in Europe,' vol. i. pp. 34, 511 et seq.). 
green sandy beds underlying this rock, although they have been also found by 
him and others in the overlying mass of the great Lower Silurian limestone, in 
t See British Assoc. Eeport for 1854. In the these casts (which are considered by him to be new 
• Proceedings of the Berlin Academy ' for June forms), and references to collateral observations 
1858, the reader will find an account of Ehren- by others, 
berg's researches on the subject, some figures of 
