1846.] SEDGWICK ON THE SLATE ROCKS OF CUMBERLAND, ETC. 127 



North America, I do not presume to judge ; but it applies to the 

 general European type as far as I have any knowledge of it. 



South of the Berwyn chain and the valley of the Upper Severn, 

 the comparison of the Westmoreland sections with the Upper Silu- 

 rian rocks is more difficult. They there appear partly as flagstones, 

 but more generally as coarse greywacke and greywacke slate, in 

 vast alternating masses thrown into continual undulations. These 

 undulating masses run far towards the south, and, if I mistake not, 

 cover very large tracts of the higher parts of South Wales. Mine- 

 ralogically they are almost identical with the hard grits (No. 3) and 

 the Ireleth slate (No, 4) of the sections of Westmoreland and North 

 Lancashire. I formerly identified them in the countries above men- 

 tioned under the name of Upper Cumbrian. During the past sum- 

 mer, Mr. Salter, at my suggestion, paid a visit to the part of Wales 

 last indicated, and the result of a traverse he made from the neigh- 

 bourhood of Builth to Aberystwyth was rather negative than positive. 

 He found hardly any fossils* ; and he was thus unable to separate the 

 great series of undulating strata, including Plynlimmon, from the 

 undulating grits and slates at the south end of the Berwyn chain. 

 This was what I expected, and what I had before affirmed as proba- 

 ble; and it induces me to place (at least provisionally) all the Plynlim- 

 mon system among the Upper Silurian rocks of Sir R. Murchison ; 

 and I believe (though I must acknowledge upon a very imperfect 

 examination, carried on only during a few days in 1832) that the 

 same upper rocks extend much farther south, and occupy by far 

 the greater part of the higher regions of South Wales ; of course ex- 

 cluding from this remark the country of the Old red sandstone and 

 the carboniferous series. But how reconcile this with the statement 

 more than once made by Sir H. De la Beche, that the Llandeilo 

 flag was repeated more than once in the undulations of South 

 Wales, and far to the north of the line of Landeilo flag drawn on 

 Sir R. Murchison's map? The answer to this question involves 

 another — what is the age of the Llandeilo flag ? 



Sir H. De la Beche has stated repeatedly that Wi^Asaplius Buchii 

 is found in some parts of South Wales among Wenlock shale fossils : 

 and among the highest beds of the Caradoc sandstone, just where 

 at Mathyrafal it passes into the upper flagstone, Mr. Salter, in the 

 year 1843, pointed out to me three or four good WeJilock shale 

 fossils, which also occur in the Llandeilo flagf. 



* A Lower Silurian Pleurotomaria however occurred at Dol-fan. 

 t The following species are common to the Mathyrafal series and the Llan- 

 deilo beds : — 



Orthis lata. Atrypa lens. 



Atrypa crassa. Leptcena transver salts. 



undata. sp. n. 



globosa. 



The following are common to Wenlock and Llandeilo beds : — 



Orthoceratites suhflexuosum. Leptmxa euglypha. 



aunulatum. transversalis. 



Orthoceratite. A smooth species (s. n.). Calymene Blumenbachii. 



Liluiles Cornu Arictis. Trinuvleus Caractaci. 



Lepieena depressa. Paradox iles fnowcrona lux, 6iC. tS:o. 



