1852.] SEDGWICK ON THE LOWER PALAEOZOIC ROCKS. 165 



a zoological question, but a question depending on the evidence of sec- 

 tions, aided by the evidence of fossils. But where was the author's 

 *' conformity of succession," proved by the evidence of good sections, 

 among his lower Silurian rocks ? He mistook the relations of these 

 rocks to the Cambrian groups, and his fundamental general sections are 

 wrong in details as well as in principle. What then becomes of the 

 lower Silurian rocks, if their names are to be tested by this canon 1 I 

 can conceive but one rational answer to this question. 



Again {loc. cit. p. 170), he tells us that "his nomenclature is 

 founded on the principle of strata identified hy their fossils'' If we 

 are dealing with elements of which we know the limits, the principle 

 stands good ; but while we are dealing with the nomenclature of a 

 new series, of which we have not made out the limits, the application 

 of this principle would be nothing better than a specious fallacy. I 

 should give an illustration of this fallacy had I attempted to call the 

 whole Cambrian series by the name of Bala Limestone ; and the 

 author has given us a frequent illustration of it in identifying the 

 same series with the Llandeilo flagstone. Were we to take the pa- 

 Iseontological evidence alone, and sink all other means of classification, 

 I believe that the massing of all the Lower Palseozoic Division of my 

 Tabular View (seep. 147) under one system of animal type would turn out 

 to be a palseontological blunder. There is a magnificent development 

 of this Lower Division in North America capable of separation into 

 two very distinct collective groups (like the Cambrian and Silurian 

 groups of the Tabular View), the upper of which is (if I am rightly 

 informed) sometimes unconformable to the lower ; and although 

 many species may be common to the two collective groups — especially 

 near their junction — yet the species most abundant in, and most cha^- 

 racteristic of, the lower are not found in the upper ; nor are the most 

 abundant and characteristic species of the upper ever found in the 

 lower. If so, the development of animal types, from the early dawn 

 of a hving world, appears to have been carried on in North America 

 in strict analogy with the development now exhibited in the British 

 Isles ; and I am greatly mistaken if the scheme of development, 

 given in the Tabular View, be not more acceptable and intelligible to 

 the American Geologists than any other scheme of arrangement of the 

 British rocks which has yet been published. 



Out of this Lower Palseozoic division M. D'Orbigny makes two 

 palceontological systems ; M. Barrande did the same virtually, though 

 not in words ; and if I may judge from my Cambridge collection, 

 as arranged by Professor M'Coy, there is as wide a separation be- 

 tween the Silurian and Cambrian groups, as between any two con- 

 secutive members of the whole Palaeozoic System of the Tabular 

 View. But I do not rest my conclusions upon this last statement ; 

 but rather upon such evidence as I have given in the previous pages 

 of this paper, and especially on the broad fact — that my original 

 Cambrian sections v/ere right in principle ; while Sir R. I. Murchison's 

 sections were, in the exhibition of his lower groups, wrong in prin- 

 ciple and conception. 



So long as my friend worked upon the plan of Dr. William Smith 



