488 



EEV. J. F. BLAKE ON THE 



sisting for the most part of rocks only recently formed and belonging 

 to the same series. As these occur towards the east, and beyond them 

 in that direction we have nothing that could so break up, whereas we 

 can find similar rock to the west, we are led to the conclusion that 

 these agglomerates, which actually stand vertically, are the higher 

 portions of the series. 2. The quartz-knobs. These have the same 

 form and character as in the western district, but some at least are 

 much fuller of rounded pieces ; still they are nearly pure quartz, 

 with polygonal network and sericite in the intervals, but no folia- 

 tion. Perhaps any one seeing one of these in this district for the 

 first time would consider it a grit, but the above characters are not 

 those of a grit. In the case of the mass at the Llangefni Mill, 

 marked " greenstone " on the Survey Map, it is so large, and shows 

 such apparent traces of bedding, and here and there in its substance 

 small flakes of foreign material, that we may conceive that this at 

 least was an external deposit whose last origin at least was sedi- 

 mentary ; but the others at Bethel, near Bodorgan, at TwU-y-mwg, 

 one mile north of Bethel, and on the railway south of Llangefni, are 

 typical isolated mounds of pure material. It will be noticed that 

 all these four masses are nearly on a line coinciding with the strike. 

 Other very quartzose knobs occur north of Cerrig Coin wen, but they 

 do not perhaps belong to this type of formation. 3. The sporadic 

 limestones. The lowest of these, near the Druid Inn, on the Holy- 

 head road, though similar to that at Bodwrog in appearance, is quite 

 distinct in structure, and corresponds to the type found among the 

 ashy series. It is a white massive rock, occupying a lenticle transverse 

 to the general bedding, and most resembles in nature and occurrence 

 the mass at Llanfaethlu. On either side of Cerrig Ceinwen there 

 are also masses of limestone, but these at the present time are of 

 different character. Though very local in development, they are 

 bedded while they last ; they are associated with reddish strata and 

 with breccias of their own substance mixed with similar material 

 (see fig. 6) and producing umber in nests. Amongst these reddish 



Fig. Q.— Quarry 1| 



south of Cerrig Ceinwen. 



6 



1 . Crystalline limestone. 2. Eeddish slates. 3- Nests of umber. 



slates are some that are marked all over with nearly parallel, 

 branching, calcareous, crystalline, cylindrical tubes, suggesting such 



