Abstract

Sir,

Regardless of the eventual resting place of the Silurian-Devonian junction in South Wales and the Welsh Borders, whether it be accepted by everyone either at the base of the Ludlow Bone Bed or at the Downtonian-Dittonian junction, the recent contributions on the subject by Westoll et al. 1971 and Turner (1971) raise important questions regarding the positioning of the upper of the two possible system boundaries. Currently, the most favoured position for the Downtonian-Dittonian boundary is at the somewhat imprecise base of the 'Psammosteus' Limestone Group in the Brown Glee Hill area of Shropshire, which is marked by a fairly abrupt change from estuarine to fluviatile conditions, and is coincident with the present known incoming of the Traquairaspis fauna in that area. Westoll et al. (1971, p. 286), aware of the doubtful value offish faunas in determining this junction, comment that it would not be unreasonable to suppose that Traquairaspis might be found below this position in the Welsh Borders, and indeed this is already the case, for, in Alteryn Quarry near Newport (Mon.), Traquairaspis pococki has been found (Squirrell & Downing 1969, pp. 38 and 45) in 2½ ft (0.8 m) of micaceous greyish green sandstone at 520 ft (I58 m) below the 'Psammosteus' Limestone. This is about 420 ft (128 m) below the base of the 'Psammosteus' Limestone Beds of Newport, which approximately equate with the 'Psammosteus' Limestone Group of the Brown Clee Hill area. This occurrence of Traquairaspis, much lower than the previously known first appearance

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