TRANSACTIONS OF THE SECTIONS. 6^ 



slates and porphyries of Arenig and Cader Idris. In Cumberland, the porphyritic 

 impress is so far continued in the ascending section, that the Coniston limestone 

 (group three), at the south end of the countj% becomes interlaced with the highest 

 beds of the second group. Hence the second group of this second tabular section 

 appears to represent, with a different mineral type, both the Festiniog and Lower 

 Bala groups. The Coniston limestone is identical, in structure and fossils, with the 

 Bala limestone; and the Coniston limestone and flagstone represent (as to thickness, 

 in a degenerate form) the whole series of upper Bala rocks (36 of the 1st tabular 

 view). 



Continuing this comparison through the upper or Silurian series, we may safely 

 identify the great zone of the Coniston grits with the more sterile portions of the 

 May Hill sandstone (Wenlock group, 4o). A part of the Ireleth slate group (5o, 

 5b, 5c), however different in structure, is in the exact place of the upper p?rts of the 

 Wenlock group (i.e.4b,4c,4d). The upper stage of the Treleth group (5rf), together 

 with a portion of a higher stage (6a), is in the place of the Ludlow stage (5a). And, 

 lastly (excepting a few beds at its base), the sixth group (of Benson Knot, Kirkby 

 Moor, &c.) unequivocally represents the upper stages of the Ludlow group (5c 

 and 5c?). 



If we assume the approximate truth of these identifications, it must be obvious 

 that the Cambrian sections are palseontologically more perfect than the Cumbrian, 

 and are therefore more fit to supply us with the means of a correct classification and 

 nomenclature. 



Returning then to the Cambrian series as defined in the first tabular view, the 

 author remarks upon its enormous thickness, its unambiguous development, its 

 physical characters, and its organic remains ; whereby it is very widely separated 

 from the overlying and generally nnconforinahle Silurian series. If the May Hill 

 sandstone be struck off from the inferior groups with which it has been classed in 

 the ' Silurian System,' it becomes (as in the tabular view) the paleeontologica!, as 

 well as the physical base, of the ' Silurian System.' For in the May Hill sand- 

 stone the great palseontological, as well as the great physical, change takes place, 

 whereby the Silurian and Cambrian groups do admit of a clear separation. The 

 Cambrian series is paheontologically quite as distinct from the Silurian as is the De- 

 vonian from the Carboniferous. 



While the May Hill sandstone, with a perfect Wenlock group of fossils, was classed 

 under one name with the Caradoc sandstone, which has a perfectly Cambrian group 

 of fossils, no wonder that Cambrian and Silurian rocks should have been regarded 

 as of one palseontological type. Now that this erroneous nomenclature and classifica- 

 tion has been corrected, the author does not believe that the two series (Cambrian 

 and Silurian) will prove to have in their fossil lists more than six or seven per cent, 

 of common species. M. Barrande's investigations in Bohemia give not more than 

 about five per cent, of species common to rocks which answer to those which are here 

 called Cambrian and Silurian. Mr. Hall's investigations in New York give, for that 

 great region, a still smaller per-centage of such common species. An examination of 

 all the fossils derived from the lower division of the palaeozoic rocks in the north of 

 England, after they have been separated into two great groups— one representing all 

 fossils found below the Coniston grits, and the other representing all the fossils found 

 from the Coniston grits inclusive, up to the base of the old red sandstone, — gives (out 

 of a total of J 65 species) not more than three and a half per cent, of species common 

 to the two groups*. 



After these facts, the author contends that there is now no rational ground of 

 dispute either as to the classification or nomenclature of the great groups of strata 

 which form the lowest division of the British Palaeozoic series. 



The nomenclature here presented has the priority in time. The physical sequence 

 was made out (as to all essential points) by the unassisted labours of the author, 

 who first adopted the name Cambrian for the vast groups which form the so-called 

 Cambrian series. The nomenclature is not only palaeontologically right, but is geo- 

 graphically true and congruous ; for every rock of which the true place had been 

 determined by the author of the ' Silurian System' is still called Silurian ; while 



* Several sections from Wales and Cumberland were exhibited in illustration of the clas- 

 sification here vindicated ; but they are necessarily omitted in this abstract. 



