Vol. 50.] OLDER ERAGMENTAL ROCKS IN N.W. CAERNARVONSHIRE. 597 



in the dip of some of the beds to the west of that hill. We notice 

 that even the map given by Mr. Blake (op. cit. p. 447, fig. 2) would 

 be more easily interpreted on our hypothesis (fig. 5 below). 1 



In attempts to connect the readings on the two sides of the lake, 

 we find there is a general correspondence. A double fault seems 

 indicated near the felsite on both railways, the throw being greater 

 on the north-east of the lake. It appears possible that the small 



Fig. 5. — Section across Mod Goronwy, illustrating the probable 

 relations of tlie beds mapped in Quart. Journ. Oeol. Soc. 

 vol. xlix. (1893) p. 44-7, fig. 2. 



Moel Goronwy. 



N.N.W 



1. Quartz-felsite. 6 & 7. Purplish conglomerate and 



3. Conglomerate. grits, passing up into banded 



4. Felsitic grit. argillite. 



8. Banded argillite. 



10. Purple Slate. 



Note. — The conglomerate north-west of the Moel Goronwy felsite appears 

 to resemble conglomerate 3 in our figs. 1, 2, and 4. The mass shown N.W. 

 of the synclinal has not been examined by us, so that its similarity is merely 

 inferred from the stratigraphical relations. 



syncline on the south-west might be equivalent to the beds occu- 

 pying the wider curve on the opposite shore ; more probably, however, 

 all the undulating beds on the former side are faulted represen- 

 tatives of the latter. But the want of exact agreement, together 

 with the fact that the beds on the rising ground on each side 

 seem to dip towards the lake, suggest that a fault may very likely 

 extend along the line of the lake itself. Such a line of disturbance 

 is shown on the Geological Survey map in the upper part of the 

 valley. 



VII. Comparison of Microscopic Sections. 



We have further examined microscopic slices of many typical 

 specimens. The following brief summary of the details and of our 



1 This must be considered hypothetical, until further examination is made 

 and the dips are recoided. We have only partially examined the section, but 

 it seemed to us that a succession was indicated in the conglomerates and grits, 

 which would agree with our interpretation of the outcrops to the S.W. and of 

 the section by the lake. 



2t2 



