184-6.] MURCHISON ON THE SILURIAN ROCKS OF SWEDEN. 4.5 



in which no fauna existed. It must, indeed, be evident that we gain 

 no additional knowledge concerning the true chronology of the earth, 

 by dwelling upon great local expansions of sediment, if no new 

 groups of animals are discoverable in them. For example, a coal- 

 field of thin vertical dimensions, whose relations are clear, is quite as 

 instructive historically, if charged with fishes, shells and plants, as 

 the enormously thick coal basin of Glamorganshire recently mea- 

 sured by Sir H. De la Beche. 



Mineral masses of very great thickness and importance doubtless 

 occur in North Wales and in the North Cumberland Mountains, 

 but no new group of fossils has been found in those tracts. This, 

 it appears to me, is the only question at issue between my friend 

 Professor Sedgwick and myself; and although in the memoir already 

 referred to he speaks of his Cambrian group, as the most remarkable 

 physical group of England, he admits that he cannot say it is charac- 

 terized by peculiar fossils* distinct from those published as Lower 

 Silurian, nor that it is physically separated from what I defined as 

 Lower Silurian by any line of general dislocation as formerly supposed 

 (see Phil. Mag. June, 184^5). Under these circumstances, and be- 

 lieving that there was no clearly-defined base-line in England for these 

 palaeozoic rocks, I have appealed to those countries in which, though 

 the mineral masses be not of such great vertical dimensions, the 

 earliest visible fossil types have been accumulated in tranquil seas, 

 and have been so raised up for our inspection as to show a decrement 

 of animal life in descending order, until all traces of organic existence 

 are lost, and the whole series is seen to repose on slaty and crystalline 

 azoic rocks. The geologist therefore ought I think to prefer this 

 simple and unbroken legend of primaeval life, to that which, however 

 voluminous it may be, is interleaved with numerous blank, torn and 

 rufiled pages, and whose earlier leaves are so nearly illegible, that they 

 have not yet been deciphered. 



In conclusion I beg to say, that if the alterations proposed in the 

 Silurian classification by Professor Sedgwick, instead of being the 

 result of researches in slaty, broken, contorted and igneous districts of 

 the British Isles only, had been arrived at in consequence of a general 

 appeal to nature's clear and normal types — or again, if even now, 

 any sufficient data should be produced (of which I am as yet 



* One of the few zoological reasons given by Professor Sedgwick for the belief 

 on his part that his Cambrian rocks may be distinguished from the Lower Silurian, 

 is that he has not fomid the Asaphus Buchii in the former. At the same time he 

 admits that the Asaphus tyr annus is abundant in his Cambrian. Now the latter of 

 these Trilobites is quite as characteristic, if not more characteristic, as a Lower Silu- 

 rian species than the other ; and surely no one who is acquainted with the habits of 

 crustaceans and their frequent isolation in special locaUties can attach importance 

 to this negative fact. The Asaphus Buchii occurs abundantly in the Lower Silurian 

 rocks of Norway together with other common Lower Silurian Trilobites of Sweden, 

 and at least 30 or 40 species which have never been found in the latter country, 

 whilst in Sweden the Asaphus Buchii is so exceedingly rare, that tracts larger than 

 those alluded to by Professor Sedgwick exhibit no appearance of it ; and so by 

 parity of reasoning I might speak of the " Odinian " or lowest group of Sweden 

 as distinguished from the lowest group of Norway, though they are in fact abso- 

 lutely synonymous. 



