1880.] Prof. Hughes, On the altered rocks of Anglesea. 347 



obvious interpretation and admit that this slatey series does pass, 

 as it everywhere appears to dip, under the gnarled series. 



Next, what evidence can be obtained from the relation of the 

 gnarled series to the overlying beds ? 



If we cross the Anglesea schists near Amlwch, we find among 

 the highest beds, limestones, conglomerates and quartzites with 

 black slates dropped in by faults here and there near Llanpadrig, 

 but whether we have in these the lower May Hill or Upper Bala 

 or something older still there is as yet no fossil evidence to 

 show. 



Succeeding the schists of the Menai Straits on the E. we have 

 the strip of black slates and shales running from near Beaumaris 

 N. to the sea near Glanffynon. These are supposed by Prof. Ramsay 

 to be the continuation of the black slates seen S.E. of the Bangor- 

 Carnarvon ridge {i.e. Arenig), the strike of which would certainly 

 carry them into this position in Anglesea. But we must remember 

 the proved faults which have entirely interrupted the continuity of 

 the strata across the Menai Straits. Moreover though fossils are 

 scarce in these beds, I detected in the basement beds of the upper 

 slate series at Glanffynon some Encrinite stems and a large Orthis 

 about the size and outline of 0. alternata, Sow., and though these 

 fossils are too illpreserved for determination, they will hardly do 

 for Arenig forms. So the evidence is that the beds are much 

 higher in the series. If they turn out to be Upper Bala then the 

 gnarled schists must be Lower Bala beds, or the Upper Bala must 

 be transgressive over the Lower Bala beds and Arenig, an overlap 

 which we have no right to assume. If they turn out to belong to 

 the Lower May Hill group, they may rest unconformably on the 

 gnarled schists but that they can be Arenig seems to me most 

 improbable. 



The Coniston limestone and shale rest upon the Green Slates 

 and Porphyry in the Lake District, and on their equivalents in 

 Chapel-le-Dale, showing that the Green Slates and Porphyry come 

 between the Upper Bala and the Skiddaw or Arenig beds. 



So the volcanic series of Snowdon is packed in between the 

 Arenig and the Bala limestone and shale, and has here and there 

 sedimentary deposits with fossils of Lower Bala age. 



Unless we assume a number of unproved faults and allow an 

 improbable downthrow for those that are seen, the simple expla- 

 nation of the structure of Anglesea seems to be that the gnarled 

 schists rest upon a great series of black slates in which Arenig 

 fossils have been found and are overlaid by other black slates 

 which the meagre fossil evidence yet obtained refers to beds not 

 older than the Bala. 



In the upper beds of the lower black slate series S. of Amlwch 

 and Llaneilian, we have felspathic breccias, ashes and felsitic rocks 



