Reinterpretation of the Bray Series at Howth, Irish Free State

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Abstract
Among other parallels to the structures which he regarded as “crush-conglomerates” in the Manx slates, G. W. Lamplugh (1895, 586–7) mentions beds with isolated fragments in the Bray Series, at Howth, Co. Dublin. The age of this Series of slates and quartzites is rather conjectural. Fossil evidence, founded on such forms as Oldhamia, though supplemented by W. J. Kyan and T. Hallissy, who suggest Middle Cambrian (1912, 249), is inconclusive. More recently, E. Greenly proposes a pre-Cambrian age (1919, 896). The alternating (or greywacke) type of sedimentation seen in the beds recurs many times during Dalradian, Cambrian, Ordovician, and Silurian. Two schools in the interpretation of the Series have to be considered. The older school, with J. Kelly (1853, 240, 253–262) and G. H. Kinahan (1878, 12, 14) as its adherents, ascribed the fragmentation in the shaly beds to volcanic agencies, and, since they failed to distinguish cleavage from bedding, regarded many of the quartzites as intrusive. The younger school, including A. McHenry and W. W. Watts (1898, 17) and Lamplugh (1903, 6), described the breccias as produced by friction during regional earth-movements. The latter, as W. J. Sollas puts it (1893, 98), possibly extended from post-Ordovician to post-Carboniferous. While the effect of later crushing and faulting must not be overlooked, it seems necessary i n the light of recent work by E. B. Bailey (1930, 86–90), Bailey and J. Weir (1932, 429–458), and S. M. K. Henderson (1935, 487–509), t o invoke probable seismicity and contemporaneous slumping to explain the alternating beds and associated shaly breccia. A new suggestion will be advanced regarding the quartzites.

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