Vol. 57.] GEOLOGY OF MTNTDD-Y-GAEN. 29 



that village. The crushing and thrusting that have resulted in this' 

 area have been already described in the foregoing pages. In the tract 

 south-west of the Garn the principal faults still have this south- 

 easterly course ; but at and near the southern end of the hill the 

 bending of the faults and the curvature of the strike suggest that the 

 movement from the north-east has been combined with a movement 

 from some other direction, perhaps from the north. 



Y. Sttmmaey. 



The stratigraphical study of Mynydd-y-Garn and its neighbourhood 

 yields the following results : — 



(1) There are three groups of rocks, whose descending order is as 

 follows : 



C. Llandeilo, comprising the Garn Conglomerate, Grit, and Breeciay 



which passes up gradually into Black Slates. 

 (Unconformity.) 

 B. Llanfair-y'nghornwy Beds, correlated with part (probably the 



lowest part) of the Llanbadrig Series of Northern Anglesey. 

 A. GarnPhyllites, correlated with part of the Green Series of Northern 



Anglesey. 



(2) The rocks are much compressed, crushed, and faulted, and 

 the apparent order suggested by the dips is quite different from the 

 true sequence. The Garn Phyllites have apparently been pushed 

 over the Llandeilo rocks ; the latter are also overthrust by the 

 Llanfair-y'nghornwy Beds, and these in their turn by the Green 

 Series of I^orthern Anglesey. 



(3) An oolitic rock is found in the Black Slates in the neighbour- 

 hood of the hill, but the evidence is at present insufficient to correlate 

 its horizon with that of the similar oolitic ironstone of the northern 

 coast of Anglesey. 



(4) In the country to the west and north-west of the hill the 

 rocks have been extensively crushed by earth-movement acting from 

 the north, and the pre- Llandeilo rocks are largely in the condition 

 of crush-conglomerates. 



(5) Around the Garn itself and east of it the principal direction 

 of movement has been from the north-east ; south of the hill the 

 structure is perhaps the result of the interference of these two 

 movements. 



In conclusion, I wish to express my indebtedness to Prof. Watts, 

 M.A., Sec.G.S., for having again examined my rock-sections and 

 for permitting me to incorporate the results of his examination in 

 my paper; also to Miss E. M. R. Wood and Prof. Lapworth, F.R.S., 

 for kindly identifying the graptolites. 



Discussion. 



The Rev. J. F. Blake said that he was familiar with the ground 

 described by the Author, and had no criticism to offer on his con- 

 clusions. The most interesting feature appeared to be the existence 



