246 ON THE GEOLOGY AND STATISTICS 
Maur. And along the Menai Strait, as at Plas Newydd 
and I^lanidan, a reddish dun-coloured limestone, which we 
have named the Under, appears, which seems to be the 
mountain limestone that underlies the upper formation of 
the limestone of Red Wharf Bay. At Plas Newydd, three 
miles to the south of the Iron Suspension-bridge over the 
Menai, the under limestone, containing a quantity of the 
oxide of iron in its composition, makes a good water-cement, 
not unhke Terras limestone. Some kinds of the upper 
limestone, near Red Wharf Bay, are so hard, that they are 
polished, and worked into ornamental slabs. Such a kind 
occurs at Llangwyfan. 
Under this upper limestone of Red Wharf Bay rest 
various strata of different coloured sandstones. The finest 
for building is found on the southern side of Anglesea. 
As connected with the calcareous formation, great abund- 
ance of shell-sand is found on the coasts of Anglesea. That 
which is richest is brought from Red Wharf Bay, in the 
north-east side of the island. It contains from two-thirds 
to four-fifths of decayed shells. The mussel is the most 
abundant shell, but the smaller cockle is also mixed up 
with the sand. 
Marl is found in considerable abundance in Anglesea, 
and is of three sorts; the red, grey, and white, The 
white, when applied in too large quantities to tillage lands, 
is considered to be hurtful. The white occurs at Lland- 
dyfnan. When marl is burned, like lime, it is found here, 
when applied as top-dressing to grass, to bring up grasses 
not seen before in the ground, as the white honeysuckle- 
grass, the red meadow-trefoil, and the tufted vetch ; and 
it augments greatly the cut of hay. While describing marl 
as a manure employed in husbandry in Anglesea, we can- 
not omit mentioning, that, on many parts of the shores of 
this island, the larger Fuci are found pretty abundantly, 
