1845.] 615 



The coincidence of many of these fossils with those published as 

 Upper Silurian types in England is so truly remarkable, that no 

 sort of doubt can be thrown on the inference, that the rocks in 

 the two countries are of exactly the same age. The actual ex- 

 amination of the fossils has also enabled us to see, that certain 

 British species which, judging from the published figures of 

 Hisinger, were supposed to be distinct, are, in fact, identical 

 with forms previously named by that author, whose terms will 

 necessarily in all such cases be adopted. 



Whilst the whole Gothlandian group is thus unquestionably 

 proved to be Upper Silurian, a large part being undoubtedly in 

 the exact parallel of the Wenlock limestone, we might (judging 

 from certain fossils, such as the Avicula retroflexa and a species 

 of Brontes*, both found with certain Orthoceratites in a sandy 

 rock at Mount Homberg in the southern part of the island) be led 

 to think, that the true equivalent of the Ludlow rocks is also there 

 present. This is, indeed, rendered highly probable from what is 

 found to be the case in the Russian island of Oesel. 



In the Swedish Upper Silurian group there are, indeed, a few 

 species unknown to English geologists. But even these, though 

 wanting in England, are found in rocks of the same age in other 

 countries. Such, for example, is that peculiar shell the Cytlierina 

 Baltica, or a variety of it, which has been detected in Normandy 

 and Brittany, and also in the Timan range of north-eastern Rus- 

 sia. Such also is the Posidonia alata, which is, if we mistake not, 

 a fossil of the Clinton division of the Silurian rocks of North Ame- 

 rica. "We cannot make the last allusion without observing, that 

 several of the species enumerated, viz. Leptxsna depressa, L. 

 euglypha, Atrypa tumida, Pentamerus galeatus, Orthis elegantulay 

 Delthyris cyrtcena, D. sulcata, Avicula retroflexa and Hypan- 

 thocrinites decorus, as well as Calymene Blumenhachi and other 

 Trilobites, together with many corals, are identical, not only with 

 English but also with North American species of the Upper Silu- 

 rian rocks, — a striking illustration of the wide diffusion of similar 

 conditions in the early stages of the formation of the earth's surface. 



To whatever extent, therefore, future researches may prove that 

 English subdivisions are practicable in it, the Gothlandian group 

 is at any rate a most unequivocal example of true Upper Silurian 

 types, which in Sweden are quite as distinct from those of the 

 Lower Silurian rocks before described, as in the best known dis- 

 tricts of the British Isles. 



Silurian Rocks of the Baltic Governments of Russia. Lower 

 Silurian at once covered by Devonian Strata — Upper Silurian 

 of the Isles of Oesel and Dago. — Referring to a forthcoming work 

 on Russia and the Ural mountains for details concerning the Silu- 

 rian rocks of the Baltic provinces of the Empire, I will now 



* Though not published in the Silurian System, the genus Brontes has been 

 found by Dr. Lloyd in the Ludlow rocks, and even in their lower division. The 

 genus is, therefore, common to the Upper Silurian and Lower Devonian strata. 



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