120 



JOINTS. 



Upper 

 Gallery. 



Wall-case 46 



6. — Lias limestone, coast, 2 miles 



t I 



Cardiff 



South Wales. Map 36. The numbered and the oppofite 



of 



The other sides are joints 

 slightly wavy, forming a rhomb. 



7. — Sandy slate, Devonian, near Topleundy Hole, Cave 

 on Coast, St. Minver, Cornwall. The upper and under 



feet rhomb. 



rfc 



The sides are joints. Imper- 



8. 



Micaceous sandstone, 



Biolch-y-fridd near Newtown 



Denbighshire 



faces are planes of 



sandstone, 

 The num- 



mica lying in them. The other sides are joints forming an 



Those at the sides are slightly curved. 



irregular rhomb. 



9. 



Slate-pencil rock, Shop, Cumberland, Lower 



Silurian. 



ments, afterwards cut into pencils. 



jointed f 



; Similar rocks occur in a great sea cliff of Lower Silurian 

 rocks, Ramsey Island, opposite St. David's, Pembroke- 

 shire. 



10. — Tilestone, uppermost beds 



Upper Silurian, 



Longhope, Gloucestershire. Map 43 S.E. The numbered and 

 opposite sides are planes of bedding, the ends are accidental 

 fractures, and the other two sides are joints, lying approxi- 

 mately in the same plane. 



11.— Felspathic slaty rock altered. Lower Silurian, 

 (Caradoc or Bala be< 

 shire. Map 78 S.E. 



) Pass of Llanberis, Caernarvon- 

 The numbered and the opposite sides 



if 



joint 



rfc 



irregular 



The under surface is partly a joint, ending in an 



The direction of the opposite joints 



fracture. 



nearly coincides. 

 12. 



>c/e. Llyn-Padam, Llan- 



S.E. The direction of 



beris, Caernarvonshire. Map 78 



the bedding is shown in the green and purple lines at the 



end marked x . 

 cleavage. 



front and bach surfaces are planes of 

 and under surfaces are joints nearly 



parallel, the regularity and continuity of which have appa- 



8 



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jits o: 



tie 





a 



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25, 



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