236 E. HILL AKD X. G. B0NNEY ON THE 



and there may sometimes be contemporaneity in these as in biological 

 phenomena. Now neither at St. David's, the Longmynds, Llanberis, 

 nor Harlech is there evidence of volcanic action in the (Survey) 

 Cambrian. Yolcanoes were active in the Lake district (as described 

 by Mr. Clifton Ward) during the Lower Bala period of Sedgwick 

 (Upper Llandeilo of Survey) when the Borrowdale series was de- 

 posited, and some of these rocks are most difficult (as has been 

 already said) to distinguish from those of Charnwood. Further, 1 he 

 strike of the Borrowdale series, when last seen near Ingleborough, 

 north of the Craven fault, is different from the ordinary strike 

 of the Lake country, and roughly parallel to that of Charnwood. 

 The rocks also of Cader Idris, and the neighbouring hills, which 

 belong to this or some part of the Arenig epoch, present great 

 lithological similarity, while there is but little to the Cambrian 

 rocks of Llanberis, of the Harlech axis, or of the Longmynds. 

 Hence it would seem far more probable that the Charnwood rocks 

 belong to the same age as the Borrowdale series of the Lake district 

 than to that of these Cambrians. 



It must, however, be admitted that within the present year 

 (1877) the argument for a Lower Silurian age has been weakened, 

 without, however, materially strengthening that for a Cambrian, 

 by the discovery (by Mr. Hicks) of agglomerates in the Precam- 

 brian rocks of Wales. Further the valuable and interesting obser- 

 vations of Mr. S. Allport* on the Wrekin introduce an additional 

 complication. He has shown that ridge to consist to a very large 

 extent of agglomerates with rhyolitic lavas (probably interstratified). 

 One of us has had the opportunity of examining these remarkable 

 rocks under his guidance. They have a strike roughly W.N.W. or 

 a little W. of that, and there is great unconformity between them and 

 the quartzites which flank the ridge. If, then, the latter rocks, in 

 accordance with the views of Mr. Callaway, are at least of the age 

 of the Hollybush Sandstones, i. e. not more recent than the Lin- 

 g-ula-flags, it is very probable that the central ridge of the Wrekin, 

 like the Malverns, is Precambrian (though much less highly 

 altered). Lithologically, however, many of our Charnwood rocks 

 seem more closely related to the volcanic products of the Lake 

 district than to these devitrified rhyolites and pitchstones. At 

 Lilleshall, however, to the N.E., is a small ridge, apparently be- 

 longing to the same series as the Wrekin, but probably rather 

 higher up in it, in which some beds more nearly resemble the Charn- 

 wood rocks ; and, finally, the analyses which we have obtained 

 during the last few weeks of some of the fragments in the older 

 parts of the Charnwood series show them to be richer in silica 

 than, from their appearance, we had anticipated, for they even 

 exceed in this the Wrekin pitchstones f. Hence, should the Pre- 

 cambrian age of their nearer neighbours be established, we must 

 admit now that there would be much more real ground for refer- 



* Quart. Journ. Geol. Soc. vol. xxxiii. p. 449. 



t It is worth noting that the rhyolitic fragments occur in the lower part also 

 of the Charnwood series. 



