S ince my return to North Wales, the proximity of Anglesey has made it possible (in intervals of my survey of the country about Bangor and Carnarvon) to seek further light on the unsolved problems of the Mona Complex; and some of the results are embodied in the present paper. I. T he A ge of the M ona C omplex . Pebbles derived from the Mona Complex had already been found in Cambrian rocks ranging from the Bron-llwyd GS-rit down to the basement conglomerates of Carnarvonshire. Fragments have now been obtained from much lower horizons. For the massive conglomerate of Bangor cannot be later than Cambrian, and it is certain that, at any rate, the lower portions of the Bangor Volcanic Series (with which portions alone we are concerned in this paper) must be much older than that conglomerate. The Volcanic Series being essentially pyroclastic, fragments other than those of the contemporaneous volcanic rocks are rare. The agglomerates, however, have yielded a few fragments of Gwna quartzite and jasper. These fragments are not schistose. But in a slide [E 1539], cut from an agglomerate between the Workhouse and Hendre-wen Lane, there is a beautiful oval fragment (fig. 1, p. 335), about ⅛ inch long, of undoubted Penmynydd-Zone mica-schist, well-foliated and holocrystalline, with sphene, zircon, and a pale epidote. It is, therefore, certain that, before the eruption of this ancient volcanic series, the Penmynydd anamorphism of the Mona Complex was complete. II. T he G wna B eds . New Analyses of the Quartzite. At the time of the issue