ASSOCIATED ROCKS OF THE BRETDDEX HILLS. 539 



a quarry near the old mill, marked by an arrow on the Survey Map, 

 I have obtained — 



Monograptus colonus, Lapw. 



Orthoceras, sp. 



Above this are sandy laminated shales, exposed at the County Bridge, 

 dipping 49° S. 10° E. 



A fourth section goes S.E. from Sale, near Buttington, to IJcheldre, 

 and shows purple shales at the base wrapping round the little anti- 

 clinal of Cambrian rock ; these pass up by alternations into grey 

 Wenlocii shales, but all these rocks are much contorted near the 

 Cambrian patch. Fossils are found in the Lower Wenlock of Sale — 



Mouograptus vomerinus, Nich. 

 Orthoceras subundulatum ?, Port. 



Near IJcheldre a quarry with shale dipping 40° S. 20° E. yields — 



Monograptus Eoemeri, Barr. ; 



and the neighbouring brook running to Lower Heldre, where it 

 crosses the road, shows dark grey shales with — 



Atrypa reticularis, Lmn. 

 Ehyncbonella nucula. Sow. 

 boreahs, Schloth. 



So we must class these beds with the Upper AYenlock. 

 Summing up the Silurian, there seem to be 5 zones : — 



TT 1 . • [1. Pentamerus Beds 1 r^ncM 



Valentian .- ^ 2. Purple Shales ^ ^^^ 



3. Lower Wenlock 



Salopian < 4. Upper Wenlock j- about 2500'. 



[ 5. Lower Ludlow 



To zone 3 belong the beds with Cyrtograpsus (?), where Hargrave 

 Brook crosses the railway, the beds of Coppice House and Sale. We 

 must place between 3 and 4 the rocks of Glyn and Llwyn-Melyn. 

 To 4 belong those of Winnington (c), Mill on Dingle Brook, and 

 IJcheldre ; and the beds of Trefnant and the Hose and Crown must 

 be grouped in 5. 



Although the Silurian usually dips at a lower angle than the 

 Cambrian, particularly near the junction, the variation in dip is so 

 great that we cannot use this as any proof of unconformability ; but 

 quite sufficient exists in the presence of bands containing Middle Bala 

 and May- Hill fossils respectively, so near to one another as in the 

 different exposures in Middletown Hill and to the south. 



y. Igneous Hocks. 



1. Older Series. 



These occur in Moel-y-Golfa, and are for the most part well 

 exposed on its crags. They appear to consist of a set of lavas 

 belonging to an andesitic type, somewhat of the character of the 

 andesites described by Mr. Teall in his paper on the Cheviot rocks* ; 

 but I think it highly probable that some of the steeper bosses of rock 

 * Geol. Mag. dec. ii. x. p. 100 et seq. 



