BATE OF EKOSION OF THE SEA-OOASTS OF ENGLAND AND WALES. 901 



In the railway-cuttings south of Penarth, not far from the cliffs, the lower beds 

 of the Lower Lias have been exposed. It is noteworthy that not only are the beds of 

 limestone much broken up here and there, but the broken-up masses of limestone are 

 ■waterworn into forms as irregular as flints, although the surface soil is a stiff clay. 

 During the summer of 1887 wide fissures were opened in the ground, cracks extending 

 to a depth of 4 feet ; and in this way rain-water would readily find its way through 

 otherwise impervious strata into porous beds below. 



North of Lavernock great cracks are formed in dry weather parallel to the cliffs ; 

 and these are sources of great weakness, leading to slips and gradual waste of the 

 cliffs. 



From Penarth southwards to Lavernock Point the beds shown are the same as in 

 Penarth headland. The cliffs run north and south, facing the east, and while for the 

 most part 50 feet high, they attain a height of 100 feet above the Roundbush Rocks, 

 S.E. of Lower Penarth. They exhibit a synclinal to the south of Penarth, faulted to 

 a small extent in four places. Further on the beds rise in an antichnal, so that the 

 Red Marls at one point form the entire portion of the low cliff. At Lavernock itself 

 the beds dip sharply to the south, and the Lower Lias limestones and shales form the 

 headland, with ledges of limestone protecting the coa.st and running out seaward. 

 Alabaster was formerly worked in a ' cave ' driven in the Red Marl at the base of the 

 cliffs, about half-way between Penarth and Lavernock ; but I was informed in 1887 

 that it had not been worked for about fifteen years.' 



Rock platforms are shown at low water along the stretch of coast from Penarth 

 headland to Lavernock. At high water the sea ordinarily touches the cliffs at many 

 points, and the headlands are impassable, including a projecting bluff of red marl 

 overlaid by grey marl north of Lavernock. Along this portion of the coast the 

 easterl J' gales alone produce much effect on the waters and cause damage to the cliffs. 



The beach nowhere shows any great thickness of recent accumulations, but for 

 some distance midway between Penarth and Lavernock there is much boulder-shingle 

 at the base of the cliffs, and small patches of local detritus are shown here and there 

 on the shelving rock-platforms. There is a spit of boulder-shingle at Runny Point. 



From Lavernock Point the cliffs run south-south-westwards, and immediately 

 1^-est of the point are composed as follows, the heights being 50 feet at the point, 

 and 1 10 feet further west : — 



Lower Lias — Limestones and shales 



Chiefiy grey marls, with here and there stone- 

 beds ........ 



Limestones and shales 



The beds occupy a synclinal, the lower beds of limestone, &c., forming bluffs at 

 either end of this stretch of cliffs, the grey Lias marls descending to the beach-level 

 between. Platforms of rock and marl extend seaward for 8 or 10 chains at the foot 

 of the cliffs, near which there is in places an accumulation of boulder-shingle and 

 sand. 



By Ball Cottage, south-west of Lavernock, there are reefs of Dolomitic con- 

 glomerate, with boulders of this rock on them. In the small bay to the north the 

 beach comprises a little sand in places, but consists mostI_v of boulders of Liassic, 

 Ehaetic, and Triassic rocks, forming one slope. Under the cliffs, about 10 yards of this 

 slope rise above the ordinary high water, then come 2 chains of beach, and reefs of 

 rock (hard grey Rhastic marl) further out. The cliffs here are protected by shrubs. 



Along this line of coast the westerly, south-we.sterly, and southerly gales are all 

 very destructive, and their influence is shown in a marked manner on the trees and 

 shrubs. 



Sully Island is composed of red, pale buff and grey Triassic limestones and marls, 

 gently inclined towards the mainland, resting on the upturned beds of the Carboni- 

 ferous limestone. The severance of this island is due to the more rapid denudation 

 of the Triassic beds, which now at low tide connect the island with the mainland, 

 while the platform of Carboniferous limestone has better withstood the action of the 

 breakers. 



Barry Island is largely formed of similar rocks, with also Lower Lias and Rhsetic 

 beds. Owing to the recent dock- works it has been connected with the mainland. The 

 Carboniferous limestone has a seaward dip, and forms the two horns or headlands of 

 the island and the promontory just to the west. The severance of the island was owing- 



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• See Section in Proo. Geol. Assoc, for 1888. Excursion to South Wales, &c., p. 32. 



