492 EEV. J. r. BLAKE ON THE 



leading down from the church, there is marked on the Survey map 

 an isolated, tongue-like mass of granite, cut off on the north from 

 another tongue -vrhich reaches down southwards from Bodwrog 

 church. jS'ow this tongue of granite actually exists, and is sur- 

 rounded by sedimentary rocks as represented, those on the western 

 side being different from those on the east, the former being halle- 

 fiinta and the latter grey gneiss. Of course a metamorphosed 

 sedimentary rock might be got into this position by complicated 

 faulting; but intrusion is the more obvious method. On the slopes 

 of the granite hill, the granite and halleiiuita are inextricably 

 mixed, after the same manner as at Llyn Faelog *. 



Further north the granite comes in contact with the grey gneiss, 

 and has ashy beds on the other side of the tongue. The actual 

 junction is hidden beneath the road at Bodwrog church ; but the 

 grey gneiss is disturbed, where seen nearest to the granite, and is 

 penetrated by small half-inch veins of granite. Unfortunately 

 these veins cannot be traced beneath the roadway into the solid 

 mass on the other side. Here, again, the simplest explanation is an 

 intrusion. 



Beyond this spot there intervenes a long belt of diorite, and I 

 have been unable to find a junction of any kind. Dr. Callaway, 

 however, records an exposure S.W. of Craig Llwyd, which I seem 

 to have missed, where the " hornblende-gneiss is interstratified with 

 granitoidite ;" this may be an intrusion of the granite into the 

 diorite. Also to the S.W. of Plas Llanfihangel there are gneissose 

 rocks, and others of mixed character, having granite segregation- 

 veins (?) in the midst of schistose diorite, — a sort of irregular 

 "banded gneiss," but the whole area gives very little definite 

 information. 



On the western side the boundary of the granite is not promising, 

 as it is overlain unconformably by the Ordovician grits. However, 

 at the outlier near Tafarn-y-botel there is a quarry in a beautiful 

 micaceous gneiss, which forms part of the general mass of similar 

 rock composing this outlier; but in the quarry floor there is an 

 irregular tongue of granite, quite distinct in character, and with clear 

 lines of separation. I am doubtful whether this is really intrusive 

 or due to segregation, but I strongly incline to the former view. 



In the area between the two tui'npike-roads the older rocks are 

 exposed, and south of the Star Inn the junction of the granite with 

 them, if not actually seen, may be determined accurately in position. 

 Here Dr. CaUaway sees a gradual change from one into the other, 

 though the bounding rock is certainly not a dark schist; but I see 

 an indefinite boundary such as we have elsewhere observed. 



The indications to be met with in the interior of the mass are 

 still more decisive than those on the boundary. One small patch of 

 '• Cambrian " is marked on the Survey map as occurring in the 

 midst of the granite at the farm of Maen Gwyn. This spot I 

 examined in the company of Prof. Sollas. In the sides of the 



* This seems to be the spot described by Dr. Callaway in G-eoL Mag. 1880 ; 

 but the bedding he describes does not seem to be observable. 



