524 DE. C. A. MATXEY OX THE [Oct. I913, 



of inclusions of grit, quartzite, and limestone, sometimes rudely 

 phaeoidal, sometimes irregular, and often more or less rounded, 

 and of all sizes from large ' boulders ' to tiny ' pebbles ' (fig. 6, 

 below). Yet, even in tbese shattered strata, traces of overfolding 

 can be seen, as fragments of the same limestone-band recur again 

 and again at various heights and at various places in the cliffs. 

 Cataclasis of the' strata is admittedly due to the crumpling effect 

 of compression acting differentially on hard, brittle, and less 

 yielding beds (the grits and limestones) when interbedded with 

 softer and more extensible slates, with the result that the former 

 have broken up and the latter have flowed round the fragments. 



Fig. 6. — ' Crush- con glomerate' in the cliff at Pen Cristin. 



C. A. M. photo. 



In this locality the disruption seems to have acted along the septa 

 of small overfolds or buckles in steeply dipping beds. 1 



Fig. 1 of PL XLIX represents a portion of a cliff — not on 

 Bardsey itself, but on the adjacent mainland near St. Mary's Well, 

 south-west of Aberdaron. It has been introduced to show the 

 passing of interbedded bands into a crush-conglomerate, and also 

 the deformation of a massive bed of quartzite into two wedges. 



i See G-. Barrow, 'On Buckled Folding' Geol. Mag. dec. 5, vol. ix (1912) 

 p. 518. 



