V0I.5L] THE COUNTRY AROUND FISHGUARD. , 159 



volcanic beds is thus to thin ont to the south-west. Fourthly, 

 the two small exposures of lavas and tuffs at Porth Sychan and 

 Porth Melyn are slightly higher than the last mentioned. 



Thus the volcanic outbursts are seen to have occurred in this 

 area on approximative^ the same horizons as those in Abereiddy 

 Bay. 1 But they are less split up by interbedded slates, and are 

 of greater thickness. For reasons which will be presently stated, 

 we seem to be close to the site of the old vents. 



The rough barren knolls and hillsides, with their white-weathered 

 crust and scattered blocks on the surface, are marked features in 

 the landscape. Each set of beds has some characters peculiar to 

 itself in the field. Thus dark olive-green, brecciated lava-flows, and 

 greenish lavas with conspicuous porphyritic felspars, are specially 

 abundant between Cam Fran and Bwlch Mawr. Greyish lavas 

 and coarse agglomerates, showing their pyroclastic nature in 

 weathering, are rare on this horizon. 



The Goodwick series, on the other hand, has breccias very strongly 

 developed ; and pale-greyish and dark bluish-grey lavas, banded or 

 nodular, are highly characteristic. It is near the village of this 

 name that proofs are furnished of the immediate vicinity of the 

 ancient orifice of eruption. Indeed, it is not too much to say that 

 we have here an old volcanic neck. On the foreshore and in the 

 cliffs immediately below the Coastguard Station we find, let down 

 between two faults against the banded and nodular lavas, a mass of 

 exceedingly coarse breccia. Closely-packed angular blocks of all 

 sizes from a few inches to a yard or more in diameter compose the 

 beds which, tilted on end, run as parallel ridges, 4 to 8 feet high, 

 along the beach. The blocks are confusedly heaped together, and 

 are cemented by a fine ashy matrix. Huge fragments of the banded 

 and nodular rhyolites of the cliff occur in these ridges, for the 

 breccia is really of higher stratigraphical position than these lavas. 

 At Penrhyn the maximum degree of coarseness is found, and there 

 is very little fine ashy material to bind the blocks together. As the 

 beds are traced along in the cliffs to the south-western corner of 

 the bay, the number of large fragments rapidly decreases and the 

 grey ashy matrix proportionately increases, until — at a distance of 

 only about 50 yards from the point of maximum coarseness — an 

 occasional fragment of banded rhyolite alone projects from the 

 smooth vertical cleavage-faces of the grey ashy slates which form the 

 cliff. In proportion as the fragments decrease, the cleavage of the 

 grey tuff becomes more distinct and perfect. The actual channel 

 up which the lava rose probably lies now to the north-east, below 

 the sea, but cannot be far distant, as this coarse breccia must have 

 accumulated round the lip of the orifice. 



The second locality, in which we have plainer proof that we are 

 on the site of an ancient ' neck,' is near the Caerlem farm, north of 

 Gam Gilfach, on Strumble Head. Here a conspicuous, bare, rocky 

 knoll stands out with steep rifted sides, 20 to 30 feet high, and 



' Hicks, Quart. Journ. Geol. Soc. vol. xxxi. (1875) p. 177. 



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