PROF. A. H. GEEEN ON A SECTION NEAR LLANBERIS. 79 



remembered is that the cleavage in Pre-Cambrian beds is of earlier 

 date thau that occurring in the Harlech and Llanberis series, as may 

 be shown by an examination of the fragments of the former in the 

 latter. These fragments, as he had often stated, showed the 

 original cleavage as well as the effects of subsequent crushing. 



Mr. EuTLEY remarked that he believed rocks of the class described 

 were not uncommon, as, for example, on the flanks of Snowdon 

 between Llyn Llydaw and Llyn Tejrn, having cleavage coincident 

 with the bedding. He thought the quartz-felsite described by Prof. 

 Bouney as old rhyolite might be expected to reappear, instead of 

 the beds beneath the breccia, and wished for definite information 

 concerning the character and position of the lower series of rocks 

 between the quartz-felsite and the fissile breccias exhibited. 



Prof. Hughes explained that the newer series being absolutely 

 unconformable to the older, the different beds of the latter appeared 

 below the base of the newer series successively, and the Pebidian 

 might well come in the spot indicated. 



The President stated that he knew the section described, which 

 he had visited with Prof. Hughes. The junction of the conglo- 

 merate and felsite was very obscure. In the part between P and Q, 

 in the diagram the lower part of the conglomerate, as he had con- 

 sidered it to be, has a peculiar appearance, and is no doubt the rock 

 described by Prof. Green as a breccia. At all events the section is 

 not so clear in nature as in the diagram. The section at Moel Tryfaen 

 is similar. On the south-west of Llyn Padarn one meets with a 

 puzzle of something the same kind, — quartz-felsite, then conglo- 

 merate, then (apparently) cleaved felsite, then conglomerate again ; 

 and it is not clear whether the conglomerate rests unconformably 

 on the felsite, or whether there is a series of faults complicated by 

 dykes. Professor Green's reading of the section might be the 

 correct one, but he felt very doubtful. 



