170 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 6, 



this principle that I then coloured a geological map of England 

 at the request of the Society for the Diffusion of Useful Know- 

 ledge. 



In the meantime, however, though, for the reason before assigned, 

 I had taken little part in the local question of what might be termed 

 Cambrian as distinguished from Lower Silurian, (leaving that point 

 to be finally settled by the Government geological surveyors,) I had, 

 by more extensive surveys in other parts of Europe, gathered posi- 

 tive evidences for coming to a definite conclusion respecting the 

 base of the Lower Silurian rocks. Finding that in Russia the 

 lowest fossiliferous band was unquestionably my Lower Silurian 

 group* (a view which was unanswerably sustained by the inquiries 

 of my associates De Verneuil and Von Keyserling), I further saw 

 this group in Scandinavia (with nothing but fucoids in its lowest 

 beds) resting at once on pre-existing slaty and crystalline rocks. 

 Northern Europe was first distinctly appealed to as exhibiting the 

 base of the series of animal life, and the Lower Silurian was, by 

 observations in Scandinavia, thus shown to be the protozoic groupf. 

 Then came the comparison of the lowest fossiliferous strata of 

 North America, by American authors and Mr. Lyell, with a Lower 

 Silurian type similarly related to pre-existing rocks ; and lastly in the 

 first chapters on the geology of Russia in Europe and the Ural 

 Mountains, the grounds were fully explained (i845) on which the 

 conclusion had been generally arrived at, that the Lower Silurian was 

 the protozoic or oldest type of animal life yet discovered. 



None of my opinions successively put forth from the year 1843 to 

 the present time were objected to, and I naturally therefore believed, 

 judging indeed also from Professor Sedgwick's new map of North 

 Wales ts that the question of palaeozoic nomenclature was settled. I 

 firmlythought, that however thick, however diversified in mineral cha- 

 racters, all Welsh and British as well as all foreign strata, in which 

 certain typical forms prevailed, would be included in the Lower 

 Silurian group. For what, I inferred, could it import in a nomen- 

 clature founded on the principle of " strata identified by their fossils," 

 whether the rocks termed Lower Silurian were two or three thou- 

 sand feet thick in the region where they were first described, or 

 many times as thick in the western parts of North Wales, provided 

 they were in both tracts characterized by the same groups of fossils ? 

 I knew for example, that in the very thin but undisturbed bands of 

 Russia, a greater number of species of animals had been found than 

 had then been detected on the same parallel in the greatly expanded 

 North Welsh rocks. It therefore seemed to me to matter little to 

 the geologist occupied with the history of successive races and their 

 apparition on and disappearance from the surface, that he should 

 be told of a tract, in which there was a much grander and more 

 diversified mineral character (with enormous porphyritic masses) 

 than in the region wherein he had previously described similar zoolo- 

 gical types. 



* See announcement to the York Meeting of the British Association, 1844. 

 t See Geological Journal, vol. i. p. 1 and map. 



