File:The Quarterly journal of the Geological Society of London (1881) (14770704515).jpg

Identifier: quarterlyjourna371881geol (find matches)
Title: The Quarterly journal of the Geological Society of London
Year: 1845 (1840s)
Authors: Geological Society of London
Subjects: Geology
Publisher: London (etc.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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liferous-slate group, as isproved by the following fossils from Corris and Taren y Gesail:— Monograptu3 Sedgewickii, PortL? tenuis, Portl.? Climacograpsus scalaris, His.Ortkoceras, sp. (same as the Cefn-Hendre shell). The Cardigan District.—The pale felspathic grits and black slatesof Newport Bay and Cardigan, hitherto placed in the Lower Llan-dovery series b 4 are not of this age, but belong to the Middle Balaor Caradoc Group ; as to this the fossil evidence is conclusive. Abovethese come rolling beds of pale slates and shales, then darker shalyslates, with a zone of pale felspathic grits; these also I refer tothe Bala period. The overlying shaly slates and rab are passage-beds of Caradoc-Llandovery age, presenting the gradual incomingof the Aberystwyth grits. Eeviewing the several rock-groups and their distribution, we find:—(A) The Plynlimmon grits, seen upon Plynlimmon and aroundRhyader, also probably in the hills west of Tregaron and Lampeter j GEOLOGY OF CENTRAL WALES. 163
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164 WALTEK KEEPING ON THE but they die out to the north and south of these localities. Nofossils have yet been detected in this series in Cardiganshire, except,perhaps, in the boulder-block at Gogerddan, near Aberystwyth.Stratigraphically they lie above the Metalliferous slates; and theselatter are proved, in the Llanbr)nmaer, Dovey, and other areas, tobe inferior to the Tarannon shales. Therefore, with reference to theNoedd Grug section, they must either represent the uppermost partof the Llandovery rocks or a special gritty development in the Taran-non shales. I adopt the latter view for the following reasons :—because of (1) their dissimilarity to the grits (Llandovery grits)which underlie the Tarannon shales at Llanbrynmaer, Llan yMowddwy, and elsewhere ; (2) their association with pale slate rockssimilar to the Tarannon shales of the Corwen area; and (3) the oc-currence of such a group of rocks, the Gala grits*, in this positionin the south of Scotland. Moreover, in the Taranno

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