SILURIAN FOSSILS CONTRASTED WITH CARBONIFEROUS. 



581 



Looking, therefore, steadily to the object of this work, and restricting myself to that 

 field of inquiry with which I am conversant, I distinctly maintain, what is asserted in 

 the Introduction; that the fossils of the Silurian System here represented, and amount- 

 ing in all to about 350 species, are, with the exception of a very few (chiefly doubtful 

 casts) , essentially distinct from any of the numerous and well-defined fossils of the Car- 

 boniferous System ; and further, that the Old Red Sandstone which separates these two 

 systems is also characterized by fossils peculiar to it. In testing this inference, I merely 

 require, that if the organic remains of formations of dissimilar age are compared, they 

 may be selected from well-known and clearly established geological types of such rocks. 

 Having for a series of years collected fossils from every stratum of the Silurian Rocks, 

 throughout a large region, in which the stratigraphical order is clear, I now present the 

 results. Professor Phillips had previously completed a valuable monograph of the or- 

 ganic remains of the Carboniferous System. If the naturalist will compare the figures in 

 these, the only two works yet published upon the older fossiliferous rocks, which combine 

 geological description with zoological proofs, he will at once see the truth of my position. 



Beginning with the vertebrata, are not the fishes of the Old Red Sandstone as distinct 

 from those of the Carboniferous System on the one hand, as from those of the Silurian 

 on the other? M. Agassiz has pronounced that they are so. 



Are any of the crustaceans, so numerous and well-defined throughout the Silurian 

 rocks, found also in the Carboniferous strata ? I venture to reply, not one. 



Are not the remarkable cephalopodous mollusca, the Phragmoceras and certain forms 

 of Lituites, peculiar to the older system ? 



the " Transition Rocks," Mr. Weaver arrives at the conclusion, that a large number (between 60 and 70 species) 

 of the fossils of these two systems are identical. I need not inform my readers, that my zoological data and in- 

 ferences are completely at variance with those of Mr. Weaver. 



Respecting the Irish case, it may be stated that Mr. James de C. Sowerby, whose authority is much cited 

 in the memoir of Weaver, is of opinion that all the fossils therein enumerated, p. 21, as belonging to the 

 transition limestone of Cork and neighbourhood, are, with one exception, characteristic fossils of the carboniferous 

 limestone of England and Ireland ; and therefore that they are of the same geological age as those which, in 

 another part of the memoir, are described as exclusively belonging to the carboniferous strata. 



Judging from the printed lists, Professor Phillips also thinks that the Cork limestone fossils are carboniferous. 



Mr. Sowerby coincides with me in believing, that the only fossils alluded to by Mr. Weaver, which really be- 

 long to the more ancient rocks (Silurian, &c.) are those enumerated (pp. 10, 15 et sea.). Should this view be 

 substantially correct, the south of Ireland, so far from offering evidence to contradict my classification, will 

 eventually be found to support it. 



From an inspection of Mr. Weaver's map alone, I cannot avoid surmising, that the localities where true 

 Silurian fossils might occur, are those alone where such have really been detected, as the strata in those situa- 

 tions are separated from the carboniferous limestone by large masses of Old Red Sandstone. (See Smerwick 

 Harbour, &c, on the coast of Kerry, and the east of Bon Mahon river, Waterford.) The Old Red Sand- 

 stone, that important feature of separation, being wanting in all the remainder of the country described, is 

 it hazarding too much to suggest, that some of the limestones which there occur, and which are loaded with 

 carboniferous fossils, may be outliers and remnants of the base of that system, which we know to be so vastly 

 expanded and widely diffused throughout other parts of Ireland ? 



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