350 i)E. E. OltEENLY ON TflE SUCCESSION AND [vol. IxXlX, 



follows ; although it must he remembered that stages represented 

 as distinct may have overlapped in time : — 



(13) Third generation of pegmatite (temperature still high). 



(12) Second generation of pegmatite, with ultrabasic") -p. f ,. 



selvages. I ,,,. ', 



(11) First generation of pegmatite (ultrabasic selvages), f , . 



/i a\ -d i a- * ■ ■ v j- metamorphism. 



(10) Production of gneissic banding J * 



(9) Crystallization of magma (nearly or quite complete). 



(8) Differentiation of magma. 



(7) Intrusion of basic magma. 



(6) Unknown interval (temperature high). 



(5) Granitoid banding. 



(4) Granitoid permeation. 



(3) Granitoid intrusions and thermometamorphism. 



(2) Disturbance and dynam-anamorphism. 



(1) Sedimentary rocks. 



Yet we do not know the end, and hardly anything of the 

 beginning, of the gneissic process. For our knowledge of the first 

 two stages indicated is little more than a glimpse into the nrystery 

 of these ancient rocks. 



VIII. Recapitulation. 



It may be well to summarize the principal contents of this 

 paper : — 



(1) The metamorphism of the Complex is older than the pyro- 

 clastic series of Bangor. 



(2) The Fydtyn Beds have been identified at three places in the 

 northern region, consequently the formation must be extensive. 

 It lies at the base of the Bedded Succession, between the Gwna 

 Beds and the Gneisses. Its relations add to the evidence for 

 widespread inversion, and reveal major infolds hitherto unknown. 



(3) The Penmyi^dd Zone. A small inlier shows the selective 

 nature and rapid development of the metamorphism. Siliceous 

 augen in a hornblende-schist rob that rock of acid matter. 



(4) The view that the Gneisses ai'e older than the Bedded 

 Succession is confirmed. 



(5) During the development of the basic gneisses, the separation 

 of pegmatites robbed the rock of acid matter. Foliation was 

 induced in solid rocks, and in some cases this can be assigned to 

 strain. 



(6) The parent-magma of the basic gneiss was introduced 

 after the granitoid permeation of the acid gneisses. Recognition 

 of this makes possible a revised and extended chronology of the 

 most ancient member of the Mona Complex. 



Discussion. 



Sir Jetheo Teall expressed his appreciation of the great work 

 that the Author had done in Anglesey. In the speaker's opinion 

 no part of the British Isles of equal area had been surveyed and 

 described in greater detail, or with more accuracy. The present 



