212 



ALTERED ROCKS, LLANBERIS. 



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iSSSx. t0 mdt int ° tLe surroundin g matrix, which, perhaps, was 



"Wall-case 4. 



almost completely fused. Locality as above. 



189.— Cambrian conglomerate, a little further removed 

 from No. 185. This rock is talcose. In general appearance 

 it resembles No. 188, but the alteration produced is less 

 extreme, and the component pebbles are somewhat more 

 distinct. Locality as above. 



190. — Cambrian conglomerate. — A little further re- 

 moved from No. 185 than No. 189. Base and pebbles both 

 crystalline as above, but the alteration being less than in 

 No. 189 the pebbles of the conglomerate begin to be dis- 

 tinctly visible. Some of the pebbles are of quartz, others 

 of quartz rock containing granular crystals of quartz, and 

 some of felspar. Some of them seem made of felspar por- 

 phyry, and others are of green and purple slate similar to 

 that of the neighbouring slate quarries of Llanberis and 

 Penrhyn. The conglomerate is, however, at the base of 

 the series in which the slate quarries are worked, and the 

 pebbles have been derived from an unknown older territory, 

 similar in structure to the Cambrian and Silurian rocks of 

 Caernarvonshire. Locality as above. 



191. — Cambrian conglomerate. Locality as above. 

 Further removed and less altered. The pebbles in their 

 original form are now distinctly visible. The base, from 

 alteration, is still porphyritic and contains numerous im- 

 perfect crystals of felspar and granular quartz. 



For the geological general position of these rocks see 

 Sections above, No. i and 4. The altered rocks are marked 

 Nos. 186 to 191. 



192 — Coarse Cambrian grit, or fine conglomerate, 

 somewhat talcose, consisting of numerous grains of silica 

 sometimes blue and transparent. Also small pebbles of 

 quartz rock. North-east side of Llyn Peris, near Llanberis, 

 Caernarvonshire. Map 78, S.E. 



This is the usual manner in which the Cambrian grits 

 appear in this neighbourhood in a comparatively unaltered 



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