532 THE GEOLOGY AND [Oct. 1913,. 



folds, packing them into kilted sheets, and often tearing the more 

 brittle bands into discontinuous lenticles. Movements of this class- 

 had no recognized parallel among the Cambrian and Ordovician 

 rocks of Carnarvonshire and Merionethshire. The effects of the 

 later movements were traced most readily in the variations of 

 the strike of the isoclinal structures. In this later movement the 

 crumpled sheets prepared by the earlier movements had behaved as 

 units, and as such had developed further folding and faulting,, 

 which, both in scale and in direction of trend, was not unlike the 

 folding and faulting observed among the Ordovician rocks of the 

 Snowdon syncline. 



The record of a north-west to south-east flow of ice across 

 Bardsey was interesting, and was a further justification of the 

 view that the 



' stiff clays with marine shells and boulders from the Lleyn . . . plastered to a 

 height of 300 to 400 feet along the hills between Harlech and Barmouth,' 



were due to ice encroaching from the Irish-Sea or Cardigan-Bay 

 area eastwards on to the land. 1 



Dr. J. V. Elsden referred to the petrographical interest of the 

 paper. The occurrence of post-movement olivine-dolerite dykes- 

 was especially noteworthy, as they bad not hitherto been recog- 

 nized, so far as the speaker knew, in the Lleyn district. It was 

 true that certain intrusions — for instance, the Llanberis dykes, 

 had been considered as being possibly of Tertiary age ; but these 

 contained no olivine, and could be shown to have been involved in 

 the post-Bala movement. With regard to the folded sill of granitic 

 composition, described in the paper, he would like to ask whether 

 any difference in minute structure was recognizable in the two- 

 limbs of the fold. He would expect to find the eastern limb 

 resembling an elvan rather than a granite. 



Mr. G. W. Lahplugh commented on the similarity of the Bardsey 

 rock-structures to those observed in the Isle of Man, and on the 

 difficulty experienced in reconstructing the original arrangement 

 from such shattered tangles. With regard to the glaciation, he 

 reminded the Author that along the eastern coast of Ireland the 

 ice pressed obliquely inland, so that ice from Ireland was not 

 likely to have crossed to Wales as suggested. 



Miss C. A. Raisin said that she had listened with especial 

 interest to the paper, because it revived the recollections of some 

 of her earlier geological work. She had hoped at that time tc- 

 carry on the investigation, but work in other directions had pre- 

 vented this. She rejoiced that the work was now being taken up, 

 and expressed her appreciation of the detailed survey which the 

 Author had begun to make. Her visit to Bardsey Island was 

 short ; but, from what she saw, it seemed clear that the structure 

 was a continuation of that observed in tne strip of country along 



1 See W. G-. Fearnsides, ' Geology in the Field ' Proc. G-eol. Assoc. Jubilee 

 "Vol. (1910) pp. 822-23. 



