1845.] 619 



of the Scottish and English Old Red Sandstone with the shells of 

 Devonshire and the Eifel, we had, indeed, previously observed in 

 other parts of Russia ; and I will now only add that, since the 

 former abstracts on Russia were published, the question has been 

 unequivocally set at rest even in Western Europe. In a recent 

 letter, M. de Verneuil informs me that in a collection wliich he 

 made at Gerolstein in the Eifel, M. Vogt, the friend and assistant 

 of Agassiz, has distinctly recognised the ichthyolites Coccosteus and 

 Osteolepis. 



To persons not well acquainted with the palaeozoic succession 

 the apparent passage above alluded to (for the overlying De- 

 vonian beds really much resemble the lower Silurian beneath 

 them) might seem to be very anomalous ; but extended examination, 

 and a due consideration of the causes which have operated in 

 elevating and depressing different portions of the country in 

 question, remove the difficulty. Thus, for example, in advancing 

 from the government of St. Petersburg, on the east, to Lithuania 

 and the shores of the Reval on the west, the true lower 

 Silurian group, as above defined, is first found to be overlaid 

 by the Pentamerus limestone ; the uppermost member of the 

 lower group which in St. Petersburg and to the east is en- 

 tirely absent. This overlying band, in which the Pentamerus 

 borealis Eichw., is intermixed with a few shells common to 

 the lower and upper groups, ranges by Wissenstein, Oberpahlen, 

 Shavli, Pocroo, and other places ; and finally, though no true 

 upper Silurian rocks occur on the main land, they are clearly and 

 copiously exhibited in the isles of Oesel ajid Dago. In these islands 

 there is not only a full development of most of the corals of Wen- 

 lock and Dudley, but also of many shells, which, entirely distinct 

 from those of the lower group, are to a great extent the same as 

 those which characterise the Wenlock and Ludlow rocks of the 

 British Isles, as appears by the following list, for which I am 

 indebted to M. Pander : — Catenipora escharoides, C. lahy^ 

 rinthica, F. Gothlandica, F. basaltica, F. polymorpha, Syringo- 

 pora reticulata, Aidopora serpens, A, conglomerata, Millepora 

 repens, Astrcea Cyathophyllum, &c., Orthocera lineatus, Tenta- 

 culites annulatus, Calymene Blumenbachii var. pulchella, Tere- 

 bratula dladonta, T. tumida, T. canalis, Atrypa depressa, A. 

 reticularis, A. affinis, A. didyma, Orthis orbicularis, Delthyris 

 sulcata, Avicula reticulata, Mya rotundata, Cardium striatum, 

 Cyathocrinites. 



This list indicates, not merely the existence of Wenlock and 

 Ludlow rocks, but also of the very uppermost beds of the whole 

 Silurian system, or those tilestones that form a passage into the Old 

 Red Sandstone, and which I formerly connected with that deposit, 

 but which for several years I have considered with Professor 

 Sedgwick, Professor Phillips, &c., as the upper termination 

 of the Silurian system. For in the uppermost strata are found 

 Orthis orbicidaris, Turritella obsoleta, and Turbo Williamsi, 

 all published British species of the highest Ludlow beds. 



