Cole — The Problem of the Bray Series. 7 



to have been aware of this important note, which would have greatly 

 supported the arguments now quoted from him alone. Du Noyer clearly 

 recognized that the inlier of Carrickgollogan might be an outlier, and he 

 notes at one point north of the main quartzite "dark grey soft shales 

 undoubtedly Silurian." The shales here, however, have always seemed to me 

 " undoubtedly " of Cambrian type, and Mr. P. B. Eoberts, when working 

 with me on the hill in 1921, secured at this point, from a new trial-hole 

 made for water, a sample of folded compact shale precisely like the typical 

 strata of Bray Head. 



Du Noyer's difficulty clearly arose from the apparent superposition of 

 the Cambrian rocks on their surroundings ; but superposition would have 

 rendered the absence of granite veins and of metamorphism all the more 

 unaccountable. On 17th November, 1865, Jukes approved a revision for the 

 one-inch map, in which the fault disappeared, while the main quartzite ridge 

 was broken, as in Du Noyer's six-inch map, in its centre. The colouring of 

 the area as of Cambrian age was properly retained. At some later date, the 

 thin band of shale shown on the south was reduced at its eastern end — I 

 think in error — and it remains thus shown in present issues. Without any 

 strong reason, as far as field observation goes, and without authority from 

 the six-inch map, the removal of the fault was accompanied by the carrying 

 of the Cambrian colouring further west, beyond the track leading to Barna- 

 slingan townland. 



The fault originally inserted on the map had been connected with the 

 broad structure of the country, and did not help local difficulties of interpre- 

 tation. The brief description in the memoir to sheet 121, p. 23 (1869;, does 

 not refer to the discussions that must have taken place during ten years in 

 the office of the Survey. Both Jukes andDu Noyer seem to have maintained 

 a mutually tolerant attitude ; but this unfortunately left the shrewd 

 questionings of Du Noyer to be revived by others after a lapse of twenty 

 years. J. F. Blake" remained puzzled, and says that the mass of Carrick- 

 gollogan "comes in in defiance of stratigraphy." He remarks that, if the 

 rocks are disposed according to their visible "banding," they "must be 

 faulted on all sides." There is nothing in the form of the Cambrian exposure 

 to exclude faulting. I began to map the boundaries on the plateau south of 

 the Ballycorus lead-mine for my own information sixteen years ago, and it 

 seemed natural'" in 1908 to describe the Carrickgollogan series as an inlying 

 mass, "probably bounded by faults." 



-^ " The Monian System of Rocks," Quart. Jour. Geol. Soc. London, vol. xlix, 

 p. 535 (1888). 



-° British Association "Handbook to the Dublin District," p. 8. 



