ORIGIN OP THE ROCKS AND SCENERY OF NORTH WALES. 239 



were derived must iudeed have physically resembled North Wales of the 

 present day, but, except these pebbles, uo trace of that land remains in 

 or near North Wales." Aud again on page 59, " No visible trace remains 

 of this more ancient physical geography, except the pebbles in the 

 conglomerate." 



This view has now been proved erroneous. There can be no doubt 

 that we have in North Wales actual fragments of an old Cambrian land 

 surface composed of Pre-Cambrian rocks. On the Survey map these rocks 

 are represented by a deep red* colour, indicating an intrusive rock. One 

 district extends from Llanllyfin to St. Ann's Chapel, the other from 

 Caernarvon to Bangor ; both are narrow in comparison with their length, 

 the direction of the longer axis being N. E. and S. W. 



Now, embraced within this region we have rocks of the most variable 

 character. In the Llanberis neighbourhood they are quartz-felsites, and 

 Professor Bonney has shown them to consist of old lava flows. This 

 rock has been already described, f At Caernarvon two varieties are 

 known, one a good unmistakeable conglomerate, which the veriest tyro in 

 geology would recognise in a moment, and the other a crystalline rock 

 composed of quartz and felspar, which might easily be mistaken for an 

 intrusive rock, but which is probably metamorphic. 



At Bangor another and undoubtedly bedded rock, of a fine compact 

 texture, and greenish-grey colour may be observed. Other varieties occur 

 in the areas coloured red on the map, but these are perhaps the most 

 abundant, at any rate I quote them as having come under my own 

 notice. 



When the arrangement of these rocks is examined, most decided 

 traces of stratification may in many cases be made out ; thus, to quote 

 instances from a paper by Dr. Hicks, in the " Q. J. G. S.," Vol. XXIV., 

 page 149 : — " About Pen-y-groes there are good indications of lamination 

 and bedding, and the rocks are composed of ashy materials subsequently 

 altered. A little further east bedding was clearly seen, the dip being to 

 the N.W. at an angle of 75°." 



The same general fact has been established by Prof. Hughes with 

 regard to the rocks in the Caernarvon and Bangor area. Thus, 

 "Q.J. G. S.," Vol. XXXIV., page 140, he says:— "Under the grit and 

 conglomerates which seem to form everywhere the basement bed of the 

 Cambrian, we have a series of stratified rocks, many of which are of a 

 very marked character, easy to identify and trace, others variable and 

 not very characteristic." Then follows a detailed account of these rocks 

 in the neighbourhood of Bangor. Speaking of their origin, he says : — 

 " The series can be matched almost bed for bed among the green slates 

 and porphyries of the Lake district, and like these may be referred to 

 an original volcanic action, and some subsequent metamorphism." 



*It must not be supposed that all the rocks represented by this colour are 

 Pre-Cambrian. 



tProf. Hughes holds the opinion that this conglomerate is of Cambrian age, and 

 that it is brought against the Pre-Cainbnan granitoid rook by means of a fault. 



