and the Palceozoic System of England, 495 



Historical remarks upon the origin of the Cambrian and Silurian 

 controversy. 



The '' Silurian System" with its beautiful illustrations and 

 great list of well-determined fossils, is known to all geologists ; 

 and I have already shown that in all its upper subdivisions it is 

 based on most clear and perfect evidence. On the contrary, that 

 in its two lower divisions it fails, not merely from defect of 

 evidence, but also from a positive misinterpretation of the fun- 

 damental sections on which the ^' System " was built. 



The evidence on which I have endeavoured to establish and 

 define the great Cambrian series is open to no such fatal objec- 

 tion ; but this evidence is still imperfectly known ; partly 

 because it has been given in a synoptical and scattered form, and 

 partly because it has been misunderstood or strangely misrepre- 

 sented. The whole series was made out in 1831 and 1832; and 

 if we strike out the reference to the Llandeilo flag and the fossil 

 Lingula, the descriptive explanation of the. Tabular View [supra, 

 p. 362) might be applied, word for word, to the laborious and (I 

 dare to say) successful work done by myself during nine months 

 of those two summers. 



in 1831 I made out the relations of the Bangor group and 

 the Harlech grits; and in the absence of fossils, the grits after- 

 wards became my base line of comparison between the systems 

 of Carnarvonshire and Merionethshire. I also made out the 

 symmetrical undulations of the Snowdonian chain, and the 

 sectional position of the Snowdonian fossiliferous trough, which 

 is several thousand feet above the Harlech grits. These facts, 

 with the sectional evidence from which they were derived, were 

 exhibited and described to the British Association in 1832. 

 During the summer of 1831 I also laid down, from actual 

 survey, the two great parallel bands of porphyry east of the 

 Menai, all the protruding syenitic bosses in south-western 

 Carnarvonshire, and the zone of metamorphic slate on its coast*. 



I had no difficulty in interpreting the contemporaneous trap- 

 pean beds, and the trappean shales or schaalstein of the Carnar- 

 von chain, having learnt that lesson long before in Cumberland; 



* My geological map of Carnarvonshire (with the colours afterwards 

 transferred to the Ordnance Map by Mr. Salter) has many times been on 

 the walls of the Geological Society. Mr. Darwin found fossils at Cwm 

 Idwal in 1831. They occur in the prolongation of the Snowdonian 

 trough, which had long been known to contain fossils, and were shortly 

 afterwards collected by myself. I never attempted to define the exact place 

 of the Snowdon fossils in the great Cambrian series ; but in 1832 1 thought 

 it probable that they v/ere below the Bala limestone, because they were at 

 a much less sectional distance from the Harlech grits of Nant Francon than 

 was the Bala limestone from the same grits near the Merioneth antichnal. 



