400 PROCEEDINGS OF THE ACADEMY OF [May 



The granite (haplite) and quartz-felsite, according to him, are in- 

 truded into the diorite and felsite after the production of schistosity. 



Seams of quartz and feldspar (haphte) alternate with seams of biotite 

 and feldspar (modified diorite) when the veins lie in the planes of 

 shearing of the diorite, and the result is a banded gneiss. 



The quartz-felsite forms part of the same magma as the granite. 

 Of two thin slides of the gneiss formed by schistose felsite intersected 

 by numerous granite veins, Prof. Bonney "thinks much of the mica 

 secondary." 



The paper concludes thus: " The following would seem to have been 

 the sequence of events in the central complex. Diorite was first con- 

 solidated. It was then penetrated by masses and veins of felsite, and 

 blocks of it were isolated from the main mass (or masses) and floated 

 off into the felsite. The consolidation of the felsite was the next 

 stage. Earth-pressures then affected both diorite and felsite, producing 

 scliistosity. A granite magma, usually haplite, sometimes quartz- 

 felsite, then invaded the area, penetrating the diorite and the felsite 

 in large masses, and sending into them countless veins, which commonly 

 found their way along planes of schistosity, giving rise to banded 

 gneisses." 



Summary of Results. 



"(1) The central complex of Anglesey was originally composed of 

 diorite, felsite and granite. 



(2) The diorite has been modified into an elliptical dome of dark 

 gneiss, namely, into simple gneisses by pressure, and into complex 

 gneisses by pressure plus granitic intrusion. 



(3) The intrusion of the granite into the diorite has often produced 

 fusion at the contact, sometimes with the generation of biotite in the 

 diorite. 



(4) The diorite and dark gneiss form an insular mass surrounded by 

 granite. 



(5) The felsite has been modified into quartzose and micaceous 

 schists and gneisses by pressure, and into banded gneisses by the 

 addition of granitic intrusions. 



(6) The quartz-felsites of the area are a part of the granitic magma. 



(7) Both diorite and felsite were modified into gneisses and schists 

 prior to the intrusion of the granite and quartz-felsite, which are not 

 foUated.". 



