ANNIVERSARY ADDRESS OF THE PRESIDENT. S;^ 



Sir Audrew Ramsay. The other two are undoubtedly far older than 

 at least any of the Cambrian rocks of Anglesey or Caernarvonshire, 

 and one of them appears to me to be unquestionably Archaean, 

 Their true stratigraphical relations may bo partly made out from 

 the vrritings of previous authors, each of whom has contributed his 

 share to the progress of enquiry. But I was not prepared by a 

 study of these writings for the interesting results which I have 

 myself obtained, and which I now proceed to state. 



In the first place, there is undoubtedly in central Anglesey a core 

 of gneiss which, if petrographical characters may be taken as a 

 guide, must certainly be looked upon as Archaean. In visiting that 

 district recently with my colleague Mr. Teall I was much astonished 

 to find there so striking a counterpart to portions of the old gneiss 

 of the north-west of Sutherland and Ross. The very external 

 features of the ground recall the peculiar hummocky surface which 

 so persistently characterizes the areas of this rock from the far 

 north of Scotland to the west of Ireland. If the geologist could be 

 suddenly transported from the rounded rocky knolls of Sutherland 

 or Galway to those in the middle of Anglesey south of Llanerchy- 

 medd, he would hardly be aware of the change save in the greater 

 verdure of the hollows, which has resulted from a more advanced 

 state of decomposition of the rocks at the surface as well as from a 

 better agriculture. 



When we come to examine these rocky hummocks in detail we 

 find them to consist of coarse gneisses, the foliation of which has a 

 prevalent dip to N.X.W. Some portions abound in dark hornblende 

 and garnets, others are rich in brown mica, the folia beiug coarselv 

 crystalline and rudely banded, as in the more massive gneisses of 

 Sutherland. Abundant veins of coarse pegmatite may here and 

 there be seen, with pinkish and white felspars and milky quartz. 

 Occasionally the gneiss is traversed by bands of a dark greenish-grey 

 rock, which remind one of the dykes of the north-west of Scotland. 

 There are other rocks, some of them probably intrusive and of later 

 date, to be seen in the same area ; but they would require detailed 

 study. My immediate object was attained when I had satisfied 

 myself of the existence of a nucleus of rock which, so far at least 

 as petrographical characters go, might with some confidence be re- 

 garded as Archaean. 



In the second place, another and quite distinct series of schists 

 occupies a large area in the west and in the centre and south of 

 Anglesey. These rocks are obviously in the main a clastic series. 



