Discussion on the trace of the Iapetus suture in Ireland and Britain

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Abstract
W. R. Church writes: In a very useful summary paper on the trace of the Iapetus suture in Ireland and Britain, Todd et al. 1991 favour locating the Grangegeeth terrane of eastern Ireland to the north of the Iapetus suture, thus making the Slane fault rather than the Navan fault the most important faunal boundary in the Iapetus suture zone. In discussing the evidence in favour of their conclusions, Todd et al. allude to the correlation of the Grangegeeth terrane with volcanic rocks of the Newfoundland Dunnage terrane, without however detailing those aspects of the correlation that may have a bearing on the location of the Iapetus suture. In response, I would like to argue that the evidence from Newfoundland allows correlation of the Grangegeeth terrane with the Exploits volcanic zone to the south of the Lukes Arm fault, and consequently, that tectonic models in which the Iapetus Ocean is located along the Solway–Navan line in Britain and the Lukes Arm–Crescent Lake–Red Indian Lake line in Newfoundland (cf. Church & Gayer 1973 ) remain viable options. A northerly setting is preferred by Todd et al. for the Grangegeeth terrane mainly because of the presence in this terrane of a 'Scoto-Appalachian' fauna with apparently few other faunal elements other than an occurrence of the 'Baltic/Celtic' genus Productorthis. Similarly, the discovery of a 'Scoto-Appalachian' fauna in the Cobbs Arm Limestone of New World Island in Newfoundland led McKerrow & Cocks (1977) to site the rocks of the central Newfoundland Exploits