2 Proceedings of the Royal Irhh Academy. 



at successive periods, and likewise broken throngh by faults. In the official 

 memoir to sbeets 102 and 112 (1861), and in that to sheets 121 and 130, 

 published after Jukes's death in 1869, too Httle attention is given to Kelly's 

 account of the dislocations at Howth and of the anomalous position of 

 Carricko-oUogan,^ which certainly resembles a ■•protrusion." Juke^ and 

 Du Foyer* remark, however, that at Howth the contortions make it 

 " frequently difficult to determine even the limits of the quartz rock beds." 

 Gerrard A. Kiaahan' furnished an excellent map showing how the quartzite 

 bands had become broken up at Bray Head, and floated apart, as it were, in 

 the shales ; and W. J. Sollas' emphasized in detail their sedimentary origin 

 and their frequent dislocation. He pointed out how the previously crumpled 

 strata must have been " caught in a post-Ordo\"ician squeeze," and he com- 

 pared the horizontal faults indicated by him on Howth with the far more 

 extensive thrust-planes that had been recognized only a few years before in 

 the Caledonian structure of Sutherland. He also drew renewed attention to 

 the Armorican folding as adding further complications to the district.' 



The floor on which the Bray Series was accumulated is nowhere visible. 

 Granitoid or schistose rocks probably contributed to its materials, and minute 

 detrital flakes of mica occur in the coarser bands in the shale series at 

 Carrickgollogan. The upper limit of the series has been the subject of 

 some questioning. J. B. Jukes and A, TVyley" concluded that an un- 

 conformity occui'red at the base of the Ordovician system throughout the 

 county of TVicklow, though their most striking piece of evidence," seen at 

 Moneystown, seems equally compatible with a fault. Jukes^- believed that 

 he could trace au unconformity in Ireland's Eye between black slates, 

 regarded by him as Silurian, and the slates and quartzites of the Bi-ay Series. 



^ The name is thus spelt on the Ordnance Survey 6-inch map, though geologists have 

 sometimes written it with one 1. Kelly calls the mass Shankill, correcting " ShankhiU," 

 a common and faulty spelling known to Jukes. CarrickgoUogan stands in the south of 

 Shankill townland, and Shankill village lies north-east of it. The crest was once known, 

 fairly enough, as Shankill Hill. 



s Mem. 10-2 and 112, p. 42. 



" "Notes on the Geology of Bray Head," Journ. JJ. Geol. Soc. Ireland, vol. \-i, 

 p. 188 (1882). 



^ " On the Structure and Origin of the Quartzite Rocks in the neighbourhood of 

 Dublin." Sci. Proc. R. Dub. Soc, vol. vii, p. 184 (1892); and "The Geology of 

 Dublin and its Neighbourhood," Proc. Geol. Assoc., vol. xiii, p. 98 (1893). Compare 

 E. Greenly, Mem. Geol. Surv., " Geology of Anglesey," p. 193 (1919). 



^ Compare .Jukes. Journ. Geol. Soc. Dublin, vol. vi, p. 38 (1856), and Mem. 102 

 and 112, p. 22 (1861). 



1" "On the Structure of the North-Eastern part of the County of Wicklow," Jonm. 

 Geol. Soc. Dublin, vol. vi, p. 28 (1856). 



" ItW., p. 34. 



12 Thii., p. 43 ; and Mem. 102 and 112 (1861). 



