124 



CLEAVAGE, ETC. 



"Upper 

 Gallery. 



"Wall-case 46. 



32. — Slaty conglomerate, Cambrian. North-east side 



Pa da 



Map 



This remarkable specimen is derived from one of the Cam- 

 brian conglomerates below the slate of the great slate 



quarries of Llanberis. The whole country is 



m 



tensely 



cleaved. The rocks at this point dip south-easterly at an 

 angle of about 55° to 60°, and the cleavage in the same 

 general direction about 80°. In specimens and even on 

 the ground the lines of bedding are exceedingly obscure 

 except to the most practised eye. They are coloured red 

 in the specimen and show many minute contortions. The 

 rock in its unaltered state icas a slaty conglomerate, and by 

 compression the pebbles have all been elongated in the direc- 

 tion of the planes of cleavage. 



33. — Fine gritty and slaty reds. Purple and 



B 



gwj 



S.E. The laye] 

 cation. The ni 

 coarse cleavage. 



mgor, Laernarvonshire. Map 78 

 different colours show lines of stratif- 

 ied and opposite surfaces are planes of 



34 



Slate and grit, purple and green. From the 



Padarn 



X, with 



Caernarvonshire. Map 78 S.E. 



This specimen shows lines of stratification, jo 

 cleavage. On the left is a gritty band marked 

 internal lines of wavy stratification, some of them marked 

 in red. It adjoins rather coarse slaty beds, the different 

 strata of which are marked by natural purple and green 

 lines. The plane marked A is a joint with a wavy surface. 

 The green beds are more gritty than the purple beds, and 

 the waving plane of the joint slightly rises with the gritty 

 bands, and becomes depressed in the spaces occupied by the 

 finer slaty beds. This alteration of the direction of the 

 joint is especially marked where it joins the coarser gritty 

 band marked X. The surface marked B is a cleavage 

 plane. In the larger and more slaty portion of the rock 

 the lines of cleavage are slightly wavy, in consequence of 

 the different results produced by pressure on beds of various 







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