166 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 25, 



and the geologists of his school — combining sections with fossils, and 

 never using fossil evidence as definitive mitil his physical groups 

 were well in hand — he made no mistake in principle ; his system was 

 worked out vrith consummate zeal and skill ; and in the true typical 

 country of Siluria he left but few gleanings for those who followed 

 him. But on leaving his true typical Silurian region his good fortune 

 left him ; and in following down the lowest beds of his system, he 

 hit off, both to the north and the south, a wrong type for the Caradoc 

 sandstone. It might be called a small mistake to have regarded the 

 Meifod beds as typical Caradoc sandstone, and to have figured some 

 of its fossils as characteristic specimens of that group. But, small as 

 was the mistake, it led Mr. Bowman, Mr. Sharpe, and myself into 

 a very wrong interpretation of certain sections in North Wales. 

 To them the mistake was of small moment, as it only led them to 

 give a wrong name to a single fossiliferous group : but to me the 

 mistake was far more mischievous ; as it led me to take my very key- 

 stone from an arch I had constructed on right principles and after 

 the hard and successful labour of two summers ; and it threw into 

 confusion th.e whole plan on which I had constructed my upper 

 groups. But this fact surely proves, how unmeaning fossils are in 

 determining the true, detailed, geological sequence of any new country 

 without a continual check from sections. 



But the great mistake of the "Silurian System," — and so far as 

 regards its effects upon my own work, the most perplexing mistake, — 

 was the placing the Llandeilo group over the upper Cambrian series 

 of North and South Wales ; and until this mistake was corrected, all 

 further progress in arrangement and nomenclature of the older pa- 

 laeozoic groups became impossible. Near the end of the summer of 

 1843 I found it impossible to separate the Bala limestone from the 

 calcareous groups of Glyn Ceiriog and Meifod ; but, if the Meifod 

 group were, on the interpretation of Sir R. I. Murchison, a typical 

 form of the Caradoc group, it followed that the Bala limestone must 

 also belong to the true Caradoc group. Nor was this all, — a great 

 group over the calcareous slates of Bala, which I had before described 

 as upper Cambrian, was called, both by Mr. Salter and Mr. Sharpe 

 (on supposed fossil evidence), upper Silurian. Again, on hke evi- 

 dence, Mr. Salter was compelled to call the (Caradoc) group under 

 the Denbigh flags upper Silurian. If all this were true, I knew 

 well, on the evidence of my own sections in South Wales, that a 

 considerable portion of the undulating beds in that part of the 

 Principality, as well as the gritty beds in the highest trough of the 

 Berwyn chain, must also be called upper Silurian. As before stated, 

 these conclusions were put to the test by myself in 1836, and found 

 to be erroneous. I then had a demonstrative proof that the Bala 

 limestone was not Caradoc — that the Meifod beds were wrongly 

 classed and named, — and that the geological relations of the Llandeilo 

 group were mistaken by the author of the * Silurian System.' 



It was during the interval of uncertainty, between 1843 and 1846, 

 that I was willing to modify my nomenclature, — believing, during 

 that interval, that my upper Cambrian group must disappear ; inas- 



