Hen-dy-cape1 (St Tudwal's) ooidal ironstone is of Lower Llanvirn age, based on the discovery of pendent didymograptid graptolites from a locality adjacent to the ironstone at Pen-y-gaer. These findings differ from previous published ages of Lower to Middle Llandeilo age for the Hen-dy-cape1 Ironstone (Trythall et al. 1987; Nicholas 1915). Although the publication of new graptolite data is welcomed, his interpretation is incorrect and if not rectified now will have important ramifications for future Ordovician stratigraphical work. This reply presents arguments against the conclusions of Young (1991).
The graptolite dating of Young (1991) conflicts with published acritarch ages for the North Wales ooidal ironstones, including the St Tudwal's ooidal ironstone (Trythall et al. 1987). Additionally, Young (1991) incorrectly reinterprets the original published graptolite ages of Nicholas (191 5). The original work of Trythall et ul. (1987) published ages for the North Wales ooidal ironstones based on acritarchs recovered from the ironstones, correlated with previously published graptolite ages. Three acritarch assemblages were recognized (Trythall et al. 1987): Assemblage 1 (Bryn Poeth) of Upper Llanvirn age; Assemblage 2 (St Tudwal's, Llandegai, Trefor and Betws Garmon) of Lower or Middle Llandeilo age; and Assemblage 3 (Tremadog) of Lower Caradoc age. The acritarch ages published do have limitations placed on their stratigraphical interpretation, due to the lack of other British analogues (Trythall et al. 1987; Molyneux 1988). Additionally, Trythall et al. (1987) and Trythall(l988) recognized two separate periods of ironstone deposition in the North Wales Basin, of Upper Arenig and Mid-Ordovician age. The recognition of two ironstone depositional phases (Trythall et al. 1987; Trythall 1988) agrees with the observations of Nicholas (1915), who documented two ironstone horizons of different ages in the Ordovician of the St Tudwal's Peninsula. The argument in support of a Middle Llandeilo age for the Hen-dy-cape1 Ironstone are detailed in the following.
The three principal arguments of Young (1991) for a lower Llanvirn age for the St Tudwal's ironstone are: the reinterpretation of the work of Nicholas (191 5); the presence of Llanvirn graptolites adjacent to the Pen-y-gaer quarry; and the presence along strike from Hen-dy-cape1 of Arenig age ironstones at Pen-y-gwai th.
The reinterpretation by Young (1991) of the work of Nicholas ( 1915) is in part based on the uncertainty of whether the graptolite assemblages recovered were from within or above the Hen-dy-capel Ironstone. Young (1991) states that grucilis Biozone graptolites were probably recovered from the Pen-y-gaer Mudstones, which stratigraphically overlie the Hen-dy-capel Ironstone. Most of Nicholas's material is now missing, including the more important material (Young 1991). The remaining material in the Nicholas collection indicates that graptolites came from micaceous siltstones, which Young (1991) assumes to have come from stratigraphically overlying Pen-y-gaer Mudstones. At Pen-y-gaer, these micaceous siltstones occur normally bedded within the ironstone sequence, and, in addition, a chaotic unit interbedded within the ironstone also contains micaceous siltstone. Nicholas (1915) was quite certain that grueilis Biozone graptolites were recovered from within the Hen-dy-cape1 Ironstone, 'The ore often contains streaks and