SCHISTOSE KOCKS OF NORTHERN DONEGAL. 233 



while a bed of grit in contact with it remains nn contorted, The 

 grit- bands and coarser schists occupy the shore to Porthaw. Here 

 the dip changes to 8.E., with much contortion and frequent intru- 

 sion of quartz-veins. 



Fig. 4. — Thrust-plane. 



S.E. N.W. 



At Hegarty 's Eock the strata are largely of quartzose grit. Quartzite 

 comes in for the first time. It differs from the quartzites of the 

 crystalline series in presenting even to the naked eye evidence of 

 fragmeiital structure in the occasional occurrence of angular grains 

 of quartz. The strata of grit and quartzite dip at a low angle to 

 the iS^.W., and each bed is sharply cleaved for a distance of several 

 inches from the surface inwards. J^orth of Hegarty's Eock, the 

 succession is clear, the grit being overlain by the quartzite, and the 

 quartzite by the fine and coarse schists, the whole undulating at 

 a gentle angle to the IN'.W. The beds then lie in a low broad anti- 

 clinal arch ; but the oblique foliation of some of the seams of schist 

 points to the continued action of lateral thrust. Towards Ballynarry 

 Bay the strata begin to rise to the iN'.W., and the outcrops terminate 

 at the sands of the bay in a considerable thickness of quartzose beds 

 and thin schistose bands, the whole dipping to the S.E. 



This brings us to the north-western edge of the subcrystalline 

 band. We have seen that at the eastern side fine-grained schists 

 and schistose grits prevail. West of these we have more massive 

 grits and black phyllites or schists ; and further west similar types 

 are again seen, associated with quartzites and quartzose schists. 

 The state of alteration is tolerably uniform from east to west, the 

 beds which exhibit the least crystailizatioii being perhaps the black 

 schists, occurring most conspicuously in about the centre of the 

 traverse. The dip being usually to the ^.W. and IST.N.W., the 

 thickness might seem to be considerable ; but there appears to be 

 frequent repetition by both folding and faulting, the folds at first 

 being thrown over to the S.E., then to the IsT.W., and again to 

 the S.E. This alternation of thrusts would be explained if we 

 supposed each series of folds whose axes dipped in the same direction 

 to occupy one slope of a large monocline. Though the thickness 

 of strata may not be great, there is sufficient variation from east 

 to west to show that the same beds are not repeated throughout 

 the traverse. With my scanty knowledge of these rocks, I cannot 

 say what is the true order of the strata ; but I am disposed to think 

 that the succession rises from west to east. The beds at the western 

 margin of the subcrystalline band dip away from the metamorphic 

 series, but I do not ascribe decisive weight to this evidence. 



Between Ballynarry Bay and Dunree Head. — The bay is about 

 haK a mile wide, its south-eastern boundary being formed of the 



