LOWER LIAS : PEN T ARTH 119 
At Penarth there is some difficulty in fixing the precise 
boundary between the Lower Lias strata and the Rhretic Beds, 
but where Nature has made no marked line of demarcation, it is 
perhaps needless for us to be concerned about the matter. The 
Grey Marls that occur above the Black Shales represent the 
White Lias of other localities, and, in fact, we find some layers of 
White Lias in this division at Penarth, together with a band that 
reminds us of the Gotham Stone. The fossils include species of 
Ostrea, Modiola, Plcurophorus, &c., for the most part poorly 
preserved, as the fossils usually are in this portion of the Rhretic 
Series. On top of these marls there is a bed of dark-grey and 
brown paper-shales, from one to two feet thick, that forms what 
may be termed the debateable ground between the Rhoetic Beds 
and the Lias. I should prefer to group it with the Lias, because 
a similar bed is found in many localities on top of the White 
Lias, and in situations where it clearly belongs to the Lower Lias. 
At Penarth itself we cannot decide the matter, for the fossils 
Ostrea liassica and Modiola minima, are common to the Rhaetic 
Beds and Lower Lias. 
Resting on those thin and debateable shales, we find a series of 
even-bedded argillaceous limestones and clays, yielding the Ostrea 
and Modiola in abundance, especially the former, so that they con- 
stitute the " Ostrea-beds " of some authorities here 12 or 15 feet 
thick. They contain also Pleuromya crowcombeia. These merge up- 
wards into similar beds that contain many specimens of Ammonites 
planorbis, together with A. Belcheri, A. Johnstoni, and small 
examples of Lima gigantea, so that the mass of the Lias above 
the Rhsetic Beds, for 35 or 40 feet, belongs to the zcne of 
Ammonites planorbis. These beds cap the headland of Penarth, 
and are well shown at Lavernock Point where they dip seaward 
(see Fig. 49.) ; but rounding this headland towards the west, we 
find the limestones paving the foreshore (where they exhibit their 
fossil treasures) and dipping westwards for a space, when they 
again rise, forming, in fact, a gentle synclinal. The trough of this 
is filled with a series of grey marls, not unlike those of the 
Rhsetic Beds, and I was at first much puzzled with them when 
examining sections on the new railway near Lavernock, and a 
cutting by the docks north-west of Barry Island. These marls 
and marly clays, with indurated bands, about 40 feet thick, are 
overlaid by 25 feet of limestones and clays. Unfortunately the 
upper part of the cliff west of Lavernock is not very accessible, 
and, as no fossils rewarded my labours, I could only infer that these 
marls and overlying limestones belong to the zones of Am- 
monites angulatus and A. Bucklandi zones which are, to some 
extent, represented at Penarth Headland, and in quarries east of 
the Penarth dock railway-station ; and are so well developed 
further westwards along the Glamorganshire coast. On the 
Watchet coast also, the zone of Am. angulatus appears to be 
represented mainly by grey shale and marl. (See p. 93.) 
