i52 MR. F. R. COW'PER REED ON THE GEOLOGY OE [May 1 89 5, 



cut across and displace the intrusive masses, as well as the volcanfe 

 beds and the slates. 



A small fault runs across the north-eastern corner of Pen Caer in 

 a W.N.W.-E.S.E. direction, and cuts the coast on Pen Eathawg, 

 where it can be well seen, and again between Crincoed Point and 

 Pwll Sir. 



An extensive fault, starting from Penrhyn, on the shore near 

 Goodwick, runs in a W.S.W. direction towards Carn Gelli ; on the 

 S.E. side it drops down the volcanic breccias which are strati- 

 graphically above the lavas. The beds are here nearly vertical, and 

 so is the hade of the fault, but the trend of the latter makes a slight 

 angle with the strike of the beds, and therefore truncates them. 

 On the S.E. side of this faulted mass of breccia another fault cuts 

 out the underlying lavas, and runs in a S.W. course along the 

 valley. The beds of breccia and ash strike against this fault at an 

 angle of between 20° and 30°. The impersistent and lenticular 

 character of the volcanic beds renders its course somewhat obscure, 

 but the lavas at Efynnon Druidion appear to be the underlying 

 series. 



IV. Relation oe the Eorm oe the Ground to the Geological 

 Strtjctuke. 



The highest ground is occupied by the diabase-masses, which rise 

 into rough and rugged eminences with bare craggy summits, some- 

 what resembling the Devonshire tors. On Mynydd Llanllawer, Garn 

 Eawr and Carn Enoch are good examples, while on Strumble Head 

 the line of ' tors ' stretches from Pwll Deri to Pont Iago, and Carn 

 "Wnda is a prominent object for many miles round. Near Newport 

 the most important elevation — Carn Ingle — consists also of ' green- 

 stone.' "Where the felspathic element predominates over the 

 ferro-magnesian the rock weathers white, instead of the commoner 

 greenish-brown : Garn Eechan and the eastern slopes of Carn Ingle 

 are instances. 



The flinty volcanic rocks, whether tuffs, breccias, or lavas, weather 

 with a white crust and occupy high ground, though not rising 

 to such elevations as the intrusive diabases, etc. More numerous 

 detached fragments, more angular outlines, thinner soil, and the 

 white crust characterize them in the field. 



Eor the most part the low-lying ground is composed of the slaty 

 beds ; and these tracts, being enclosed for pasture-land, or covered 

 with swamps, or cultivated for crops, afford no exposures of the 

 solid rock. Usually, moreover, drift or Boulder Clajr causes an 

 additional difficulty in tracing the boundaries or determining the 

 characters of the underlying beds. The cliffs east of Coch y Ceiliog 

 afford good sections of the slates, and their sharp ridges and jagged 

 reefs that run out into the sea, with their outlyiug stacks and 

 islets, exhibit markedly different outlines and shapes from those 

 composed of the igneous materials. 



The river Gwaen, which drains most of the district east of Eish- 



