The Bala and Llandovery Rocks of Glyn Ceiriog North Wales.

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Abstract
1. Introduction . It was in continuation of the work which we had begun at Corwen that in 1892 we paid our first visit to Glyn Ceiriog. At Corwen we had been unable to detect any decisive proof of unconformity at the base of the Corwen Grit; but in the Bala Beds below we did not find the characteristic fossils of the Sholeshook Limestone or of other Upper Bala deposits, and were therefore led to believe that the highest beds of the Bala Series were absent, and that there was probably an unconformity which was too slight to be visible in so small an area. The section at Glyn Ceiriog encouraged the hope that higher Bala Beds might there be found, and it seemed, moreover, to afford excellent opportunities for the examination of the whole Bala Series. To judge from the map of the Geological Survey, or from a cursory inspection of the ground, it would be difficult to imagine a locality more favourably situated for the purpose. The valley of the Ceiriog appears to cut through the whole of the Bala Series, from the lowest ash-band up to the Glyn Grit; and, owing to the steepness of its banks, the rocks are admirably exposed, while most of the beds are fossiliferous almost to excess. It was not long, however, before we found unexpected difficulties. The same succession, or rather the upper portion of it, should appear in the nearly parallel valleys of Tyn-y-twmpath and Nantyr; but when we examined those

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