768 ON AN UNCONFORMABLE BREAK OF THE CAMBRIAN ROCKS. 



priority of observation referred only to North Wales, where he had 

 been the first to suggest, in 1867, the existence of a series older 

 than the Cambrians, and this had led to the subsequent researches 

 of Professor Hughes and Mr. Hicks in the same direction. If, 

 as Mr. Hicks had stated (with which the author agreed), the 

 Cambrians of Moel Tryfane rest unconformably against the quartz- 

 porphyry mass, the same unconformity must exist in the Llanberris 

 railway-cutting, as it includes an almost continuous section from the 

 workable slates of the Grlyn quarries to the quartz-porphyry at the 

 N."W. end of the lake ; after a reexamination of the line of junction 

 on three different occasions, he could find no other interpretation of 

 the section in question than that of an unconformable break in the 

 series. He maintained that the stratification of the two sets of beds 

 was clearly visible, and was quite discordant in the two cases, and 

 also readily distinguishable from the planes of cleavage, which were 

 in a different direction from the stratification of both series. Even 

 supposing that the sinuous line of junction was partially due to 

 crumpling, the author considered that such interlacing and distor- 

 tion might as readily occur between beds in unconformable contact 

 as within evenly stratified deposits. 



