KATE OF EROSION OF THE SEA-COASTS OF ENGLAND AND WALES. 861 



the main bay by cliffs about 100 feet high. The sea is encroaching here, some 40 

 yards of land having been lost during the last fifty years. 



Coast from Forth-lislty to Nemgale Sands. — Porth-lisky is a small inlet excavated in 

 the softer beds C'f the Pebidian series ; it is bounded by the harder beds of the 

 Pebidian on the west and by the hard granitoid or Dimetian rock on the east. The 

 cliffs in the bay are about 90 feet high. [ They consist of a series of nearly vertical 

 beds, belonging to the Pebidian groups. Some have an ashen-like appearance ; others 

 are felsitic breccias, which decompose very readily. — H. Hicks.] The shingle in the 

 bay varies in size from gravel up to pebbles 18 inches in diameter. Old inhabitants 

 believe that it has moved up the bay about 10 yards within their memory. 



Porth-clais Creek is the outlet of the river which drains the St. David's area. The- 

 banks on each side run up from a cliffy ba.se in a sharp slope to a height of about 

 100 feet. 



During the last fifty years the sea has cut away about 40 yards of the upper part 

 of the harbour, and also some of the cliff on the west side. This is partly due to vessels. 

 which carry away ballast, but also to the wash from a heavy run in the creek during 

 S.W. gales. The pier near the mouth of the creek has been breached by the sea 

 during the last few years, thus accelerating the cutting process. 



Along the cliffs from Porth-clais eastwards to Carbwddy there have been some heavy 

 slips, but there is nothing to enable one to judge as to how much has fallen within 

 recent years. The alterations which have been made in the pathways show tliat the 

 loss must have been considerable in some places. 



In Carbwddy the shingle has moved seaward 22 yards ; the slope of the new rido-e 

 is about 23°. This gain is due to the waste from a large quarry which is worked 

 here. This shingle, being the recent waste from the quarry, is hardly formed into 

 pebbles. 



From Carbwddy to Porth-y-rhaw the waste from the cliffs appears to be less thaa 

 further west. [These cliffs consist of Cambrian rocks, chiefly sandstones and flaggy 

 beds. — H. Hicks.] 



In the cliffs under Llanunwas, extending from Porth-y-rhaw to Solva, there have 

 been very heavy slips. In one place, between a rock called the Cradle and one called 

 Gewny,the entrance of Solva Creek, the slips of the cliff have cut back fuUy 10 feet in 

 . gaps along a distance of 500 feet in about thirty years. Solva Creek has not undergone- 

 any noticeable change in that time. To the east of Solva Creek there are heavy slips 

 every winter. Between the point called Dinas Mawr and Pencwm at the north end 

 of Newgale Sands the slips have been few and of no great extent. 



This bay is excavated in Carboniferous beds, the Cambrian rocks forming the 

 north-west margin. At Cwy Mawr, where the Carboniferous rocks commence, about 

 20 yards have been eroded during the last fifty years. The cliffs at the south-eastern 

 side of the bay are also of Carboniferous rocks. Between these cliffs there is a shingle 

 beach, rather more than a mile long, with an extreme width of about 110 feet and a 

 mean width of about 90 feet; the landward slope from the summit is about 46 feet 

 long. The seaward slope, about 64 feet long, has an intermediate full, which does not 

 seem to be caused by the neap tide, as it is too wavy and irregular : it changes with 

 every gale. The pebbles vary from 3 to 14 inches in diameter ; they are sometimes 

 mixed with patches of small gravel. 



The spring tides range 17 feet ; neap tides 11 feet. 



Some people believe that the beach has travelled landwards to a considerable 

 amount, but there seems no evidence of any important change during the last eighty- 

 years. The amount of shingle is said to be increasing, and it has a slight tendencT 

 to travel from S.S.E. to N.N.W. 



Behind the northern part of the shingle beach there is a marshy alluvial flat^ 

 about 10 feet below the summit of the shingle. 



Seaward of the shingle beach there is sand, 230 yards -wide at low water ; trunks of 

 trees have been seen here when the sand has been cleared away by heavy storms. 



Giraldus Cambrensis states that in the winter of 1234, by reason of a violent storm, 

 ' the surface of the earth [at Newgale], which had been covered for many ages, re- 

 appeared, and discovered the trunks of trees cut off, standing in the very sea itself, 

 the strokes of the hatchet appearing as if made only yesterday. The soil was very 

 black and the wood like ebony. By a wonderful revolution the road for ships 

 became impassable, and looked, not like a shore, but like a grove cut down, perhaps, 

 at the time of the Deluge, or not long after, but certainly in very remote ages, being 

 by degrees consumed and swallowed up by the encroachments of the sea.' 



