J. R. Dahijns — Geology of Snoicdon. 269' 



the lower rocks are bedded near the top ; or perhaps one should 

 say it is in places convenient to include some well-bedded rocks 

 with the lower group for the sake of carrying on a line. In some 

 places, however, lines of bedding are to be seen in the heart of the 

 group (C). This is the case just above Glaslyn, on the north side 

 of the tarn, Mdiere the rocks are of an ashj' nature, and are dipping 

 at 60° to the W.S.W. near a fault. 



5. Immediately south of the outflow of Llydaw there are some 

 curious greenish rocks of a fragmentarj' character, in which, however, 

 one can rarely find any distinct bedding. They occur apparently 

 at the base of the calcareous series (B), though very unlike the 

 basement beds of that series seen hard by, and seem to wrap round 

 the upper part of C, partly owing to a roll over, but chiefly from 

 their having, as it seems to me, been deposited against and around 

 a boss of the lower felsitic rocks. They include one or two bosses 

 of an intrusive I'ock also of a greenish hue, which are probably 

 connected with the great mass of diabase that forms Clogwyn Aderyn 

 and Clogwyn Pen-llechen. 



6. I may state, as I have not seen it mentioned anywhere, that 

 the beds B are often beautifully false-bedded, or, as I prefer to 

 say, cross-bedded. This is well seen in Cwm Glas. 



7. In the same Cwm the base of the upper felstone (A) is plainly 

 to be seen running down northward from the ridge of Crib-y-ddysgl 

 to the northern end of Clogwyn Person ; and it is here manifest 

 that the felstone lies in a hollow in the underlying beds (B), for 

 it is in contact with higher beds of B on the ridge than at the north 

 end of Clogwyn Person, where the junction of the two rocks is 

 clearly seen to be a natural and not a faulted one. 



8. On Ci'ib Goch the upper felstone consists entirely of a mass of 

 blue close-grained columnar felstone showing lines of viscous flow. 

 On Crib-y-ddysgl the rock consists of two distinct parts, separated 

 by a thin band of slate or cleaved tuif. The lower part is a massive, 

 but not always columnar, felspathic rock, containing on the ridge 

 calcareous seams interbedded with it near its base. This is succeeded 

 by a thin seam of cleaved tuff, inconstant in occurrence, overlaid by 

 a columnar felstone exactly like the rock of Crib Goch. 



The section at the base, seen on the Cwm Glas side of the ridge, 

 is very interesting. The interbedded calcareous seams are bent 

 over thus : — 



N 



as if (after consolidation) the rock had been thrust from north ta 

 south over the underlying slates and ashes, against which its layers 

 had dragged at the junction. I have not yet traced the outcrop of 



