Vol. 55.] GEOLOGY OF NOETHEEN ANGLESEY. 679 



by the speaker and accounted for. These were not the difficulty ; 

 it was the stratigraphical one. If quartz-knobs were fragments of 

 old sandstones separated by earth-movements, where were these 

 sandstones, and what was the cause of the remarkable purity of the 

 material ? Some of these knobs were quite white, and perfectly 

 isolated amidst miles of dark schistose slates, etc. 



Prof. SoLLAS joined in recognizing the importance of this con- 

 tribution to our knowledge of an unusually difficult country. As 

 regards the ' quartz-knobs ' he was in complete agreement with the 

 Author; and having had, through the kindness of Prof. Blake, the 

 opportunity of studying specimens from a typical quartz-knob of 

 Anglesey, he had found in them the same characters as those that 

 distinguished the quartzites of Howth and Bray, which had clearly 

 originated from true sandstones. The joints and other fissures of 

 these masses were filled with secondary quartz, which had penetrated 

 the adjacent portions of the rock and destroyed in many cases all 

 traces of its original structure ; but the great mass of the rock had 

 escaped this influence, and afforded obvious evidence of a clastic 

 origin. The isolation of the quartzite-masses stood in connexion 

 with the earth-movements that had produced ' flow-breccia ' ; 

 indeed, the whole terrane had been forced into a state of ' flow,' 

 and the 'quartz-knobs' were phacoids of quartzite on a grand scale. 

 The quartzite and green-and-red slates of Howth and Bray would 

 require but slight alteration to acquire characters like those of the 

 Green Series of Anglesey. 



Dr. Hicks congratulated the Author on the careful manner in 

 which he had worked out the geology of an important and difficult 

 district in Anglesey. He believed that the interpretation put 

 forward by him w^as essentially the correct one, and the one to be 

 expected in an area where pre-Cambrian and Lower Palaeozoic rocks 

 had been so greatly affected by earth-movements. The Orthis 

 exhibited seemed to him to be Orthis Carausii, which is found at 

 St. David's in beds of Tremadoc age. There are conglomerates in 

 Anglesey belonging to different horizons — the oldest, he believed, 

 are those near Llanfaelog, which contain not only fragments of 

 green schists but also pebbles of gneiss and granite, and are over- 

 lain by a series of greenish and grey sandstones older than the 

 slates of Llandeilo and Arenig age. In so greatly faulted an area 

 it is extremely difficult to make out the natural succession, for series 

 of beds are frequently absent or not exposed, not from want of 

 deposition, but as the result of faults and overthrusts. 



Prof. Watts said that microscopic examination had not enabled 

 him to discern any difference between Prof. Blake's ' true quartz- 

 knobs ' and others which that observer disclaimed as quartz-knobs. 

 He had had the pleasure of working with Prof. Sollas in the 

 Howth district, and eagerly awaited the publication of the latter's 

 map. The structure of some crush-conglomerates curiously simu- 

 lates the geological map of that district — and this extraordinary 

 resemblance extends to the hand-specimens of the rock, even to the 

 very appearance of the quarries. There is no doubt that the origin 



