99 
CHAPTEE IV. 
LOWER LIAS (continued) 
LOCAL DETAILS. 
Glamorganshire and Monmouthshire. 
IN Glamorganshire the Lower Lias borders the southern side 
of the great coal-field of South Wales ; and to the west of 
Cardiff, the Old Red Sandstone, Lower Limestone Shales, and 
Carboniferous Limestone, have been denuded so as to form a 
plain that is comparatively level when compared with the bold 
hills of the Coal-region on the north. 
The Lias rests in places directly on these older rocks, and 
chiefly on the Carboniferous Limestone. In this district, as on 
the Mendip Hills, the Dolomitic Conglomerate had previously 
stretched in irregular masses over the Carboniferous Limestone, 
&c., so that the overlapping presents irregular modifications, the 
Lias resting here and there directly on the Dolomitic Conglomerate 
without the intervention of the Rhaetic Beds.* 
The peculiar characters of the basement-beds of the Lower 
Lias, where they rest on the Carboniferous Limestone, at Southern- 
down and Dunraven near Bridgend, and at other localities in 
Glamorganshire, were pointed out many years ago by De la Beche ; 
he noticed that the limestones became more or less conglomeratic, 
and were associated with a whitish limestone known as Sutton 
Stone.f 
Since the recognition of the Rhaetic Beds in this country 
(1860-61), there has, however, been much discussion on the age 
of the " Lias conglomerate " of South Wales, and on the question 
whether the Rhaatic Beds are or are not represented in it. 
In 1863 Mr. R. F. Tomes "claimed for the basement-beds a date corre- 
sponding to the Rhaetic age," on account of the presence of Plicatula 
intusstriata ;J but this view proved to be based on an insecure foundation, 
for the species occurs sometimes abundantly in the Lower Lias. In 1866 
E. B. Tawney expressed his opinion that the whole of the Conglomerate 
series was Rhaetic in age ; he divided the beds as follows : 
2. Southerndown Series (about 50 feet thick at Southerndown and about 
12 feet at Dunraven). 
1. Sutton Series (about 40 feet thick). 
The ordinary beds of Lower Lias, overlying the Southerndown Series, were 
grouped by him in the zone of Ammonites Bucklandi. 
Tawney's conclusions were shortly afterwards contested by Charles Moore, || 
H. "W. Bristow,1T and Prof. Ralph Tate,** who maintained that the beds were 
* See also De la Beche, Mem. Geol. Survey, vol. i. pp. 240, 252, 274. 
t Mem. Geol. Survey, vol. i. pp. 269, &c. ; Geol. Observer, Ed. 2, pp. 482, &c. 
I Proc. Cottesw. Club, vol. iii. pp. 191, 202. 
Quart. Journ. Geol. Soc. vol. xxii. p. 69. 
|| Ibid., vol. xxiii. p. 511 ; and Proc. Bath Nat. Hist. Club, 1865. 
IT Ibid., vol. xxiii. p. 199 ; see also pp. 202, 208. 
** Ibid., p. 307. 
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