Silurian Rocks of North Wales, Sfc. IdS 



geologist reaches the chief fossiliferous zone of the north-western por- 

 tion of Wales, as exhibited in the range of Snowdon. 



He also points out that the same beds with Lingula occur along the 

 Merioneth anticlinal in the valley of Festiniog, and that in proceeding 

 westwards therefrom, a grand succession is seen up to the well-known 

 horizon of Bala. Admitting that the Lingula of these low beds in 

 North Wales is a new species, that single circumstance cannot surely 

 be of much value in a discussion like this. Lingulce occur in nearly 

 all the formations or subdivisions of the Silurian system of Britain, 

 from the Ludlow rocks to the Llandeilo flags, whilst in North Ame- 

 rica, as in North Wales, they are found at the base of tlie whole of 

 the same series of animal life. Again, in Russia, where fucoids 

 only have been detected in the lowest strata, the shells immediately 

 above them are Orbicuisc and 4Jngulites (Obolus), both of them, like 

 the Lingula, small horny bivalves suited to a sandy or muddy sea- 

 bottom in which there had been little calcareous matter. In North 

 Wales, as in other paltcozoic countries, the true test of the age of the 

 rocks lies in the lowest zones in which the common and characteris- 

 tic fossils are found. Now, among the lowest of these North Welsh 

 bods, Professor Sedgwick mentions the Asaphus Powisii, a crusta- 

 cean first described by myself from the very uppermost beds of the 

 Caradoc sandstone of Shropshire, or rather from the Horderley lime- 

 stone at the base of the Wenlock shale, its associated fossils near 

 Trcmadoc, being Graptolites MurcJiisonoi and G. foltaccus, both com- 

 mon Silurian forms. A Homalonotus is next cited as pertaining to 

 still higher beds, and is identified with a species from the Lower Si- 

 lurian beds of Wittingslow in Shropshire. 



The Lepteena sericea, a species frequent in the W^enlock shale, and 

 which also ranges, as I have shewn, throughout the Lower Silurian 

 rocks, is said by Professor Sedgwick to run low down into the Snow- 

 don ian group, together with the Trinucleus Caractaci, the most typi- 

 cal perhaps of all the Caradoc fossils ; whilst the associated Orthidaa 

 are nearly all the very same simple-plaited species figured in my 

 work, and on which I have always dwelt as the best and surest types 

 of the Lower Silurian strata; viz., Orthis calligramma, 0. vesperti^ 

 liOf 0. Jiabellulum, 0. Actonice, 0. expansa^ 0. elegantula, 0, JPecten^ 

 &c. 



Let these species be fQund in any part of the world, and I ask if 

 their discoverer can possibly assign to them any other geological name 

 than Lower Silurian fossils? 



And here I would say a few words on one of the propositions of 

 my friend Professor Sedgwick. Changing the old name *' Lower 

 Silurian" into the new one of" Cambro-Silurian," and shewing that 

 there is a considerable intermixture of Upper and Lower Silurian 

 forms in the group, he states with justice, that it should never have 

 been cut oft* from the Cambrian. But why was it so cut off ? — simply, 

 I repeat, because the zoological contents of tho great mass of the 



