236 



MESSES. T. C. CANTEILL AND H. H. THOMAS ON THE [May I906. 



in the road northward, both in the road and in the hedgebanks for a 

 distance of 17 yards. The hedgebank shows a section, in what 

 looks like a more basic variety of the diabase, and this type 

 continues up to the junction of the intrusive rock with the rhyolites, 

 which may be located to within a few inches. At the junction the 

 diabase is exceedingly rotten, and has been sheared against the 

 harder rhyolites. The rhyolite at the junction has a flinty margin 

 without spherulites, but is immediately succeeded by a beautifully- 

 spherulitic rock. The mass of sediments in the section is either a 

 patch caught up in the intrusive rock, or a bed lying between two 

 tongues of diabase. These sediments, however, present no recog- 

 nizable signs of metamorphism. 



Although no other exposures of solid rock are seen, from the loose 

 pieces of diabase scattered through the soil of the tract between 

 the road and Pentre-newydd Farm, it would appear that this area 

 also is occupied by the intrusive rock. 



Pig. 3. — Geological map of the country around Capel Bethesda, 

 on the scale of 6 inches to the mile. 



EEH Tetragraptus-Grits 

 IIIHIH Tetragraptus-Shales 



Diabase 

 H Rhyolites 



BasaLGreen.Beds of Old Red Sandstone 

 M Red Marls etc. of Old Red Sandstone 



(2) The Rocks at Capel Bethesda. 



The igneous rocks in the neighbourhood of Capel Bethesda occupy 

 a narrow strip of country, following the road from Glog to the 

 four cross-ways north of Pen-gelli-uchaf. The rocks consist of 

 rhyolites and a rotten diabase. 



