8 Proceedings of the Royal Irish Academy. 



There was here no suggestion that it might rest upon a fanlt-plane. The 

 problem of its relations with the Leinster granite still remained. This, how- 

 ever, becomes simple if we dismiss the horst theory, the theorj- of protrusion, 

 accept Du Noyer's view of the local sequence, and regard the wliole Bray 

 Series in the County of Wieklow as imported into the region by thrusting 

 from the east. In 191i, writing on East Leinster for the Cambridge 

 Geographies, I suggested that the Cambrian series had been banked up thus 

 against the Leinster chain, and that CarrickgoUogau, though technically an 

 inlier, should be regarded as an outlying "klip." Events since then have 

 delayed publication, and the passage is only now in type. The idea may 

 have occurred to several geologists, but it removes so many difticulties that it 

 seems well to inquire what its acceptance will involve. 



III.— The Widee Problem. 



The Bray Series, like the Mona Complex," must have been formed on a 



floor of still older crystalline rocks. Whether it is of Cambrian age or not, 



Upper Cambrian strata probably once extended over it. These may have 



been removed by denudation, as in Anglesey," in early Ordovieian or late 



Cambrian times. Since Arenig strata occur in Anglesey, a Cambrian date 



seems likely for this considerable epoch of erosion. Then followed the 



Ordovieian overlap, and the marine Arenig strata, with Clmiograptus fleoyilis, 



recognized by Dr. Gertrude L. Elles'' at Courtown, in the north of the county 



of Wexford, were no doubt deposited in continuity with those of Wales. The 



sea-floor sank, and Gotlandian (Upper Silurian] strata followed in regular 



succession. The next break was caused by the mountain-building of the 



Caledonian epoch. The Leinster chain rose, and the granite cauldron in its 



core produced considerable metamorphism of the encasing Ordovieian rocks. 



The part of the Bray Series that we know, which is probably only the upper 



section of a contorted system, lay, however, weU beyond the zone of danger. 



The late Cambrian denudation had swept away, not only its cover, but also 



its westward prolongations. When the Caledonian crumpling first began to 



rear it from its bed, this residue of the upper mass still lay eastward of the 



cauldron, though the western part of iis foundation was no doubt traversed 



by the granite-magma as it rose into the Ordovieian arch. The granite came 



into place very largely by corrosive action ; but in time it cooled, and no 



longer sent out veins into its walls. The Caledonian earth-movements 



continued, and a thrust-plane broke the crest of the range in the North 



=' E. Greenly, " Geol. of Anglesey," p. 169 (1919). 



"■^HM., p. 402. • 



^ Letter in Irish KaturaUst, vol. six, p. 244 (1910). 



