THE CAMBRIAN ROCKS NEAR LLANBERRIS. 767 



he had previously been inclined to accept Mr. Maw's interpretation, 

 yet on a critical examination of the appearances presented by the 

 section he was unable to admit the existence of the unconformity at 

 the point where it was placed by the author. He argued that the 

 appearances described by Mr. Maw were not such as are usually 

 exhibited in cases of unconformity, in which we may expect to find 

 evidence of elevation and denudation and the formation of littoral 

 deposits, composed of pebbles derived from the older rocks, at the 

 line of junction of the two series. 



Prof. Hughes defended the view expressed in his paper read 

 before the Society in December, pointing out that the supposed un- 

 conformity occurred in the middle of the well-known green schists 

 and sandstones which formed the lowest Cambrian beds, and not at 

 the base of any well-marked group ; that the jagged edge of the 

 slate was not the kind of surface likely to be left by such a denuda- 

 tion as must have taken place at the commencement of the Cambrian 

 period ; and that there was no conglomerate or other evidence of 

 such denudation along that line. He considered that the divisional 

 planes below the supposed unconformity, which Mr. Maw took for 

 bedding, were due to cleavage. 



Prof. Ramsay stated that the section referred to by the author, 

 which was exposed in a railway-cutting, was examined by himself 

 and Prof. Huxley with the assistance of Mr. Maw's own drawings, 

 and that they both came to the conclusion that there was no proof 

 of an unconformity such as that insisted on by the author. He 

 maintained that there was a natural passage from the quartz-por- 

 phyries up through the conglomerates into the beds lying above 

 them, and denied the possibility of separating the pebbles imbedded 

 in the conglomerates in the manner which had recently been 

 described. After a long and careful study of the junction, he had 

 come to the conclusion that there was a gradual passage between 

 the two series, as stated in his ' Geology of North Wales,' a new 

 edition of which will shortly be published. Hence he was led to 

 regard these masses of quartz -porphyries as representing rocks of 

 Cambrian age excessively metamorphosed through pressure in the 

 manner which had been suggested by Mr. Mallet and himself. 



Prof. Seelet indicated that a crucial test to which the views of 

 Mr. Maw and those of his critics might be subjected would be 

 afforded by examining if the planes of cleavage in the lower rocks 

 passed into those above. 



Prof. Hughes, in reply to Prof. Seeley, stated that the cleavage, 

 though less strongly marked among the sandy beds, distinctly 

 occurred above and below the supposed unconformity. 



Prof. Ramsay said that both porphyries and slates were traversed 

 by the same divisional planes. 



The President, without wishing to prejudge the question, re- 

 marked that the drawings exhibited by the author greatly resembled 

 the appearances presented in some undoubted cases of crumpling and 

 distortion by cleavage. 



The Author, in reply to Mr. Hicks, said that his remarks about 

 Q. J. G. S. No. 135. 3 e 



