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Pladda
PLADDA, a low rocky islet in the frith of
Clyde, about 5 furlongs south of the south-eastern extremity of Arran,
and divided from that island by a strait to which it gives the name of
Pladda sound. Mr. Galbraith, in 1836, determined its position to lie
N. lat. 55° 25' 33"; W. long. 50° 7' 0". Stratified rocks, consisting
of a white sandstone accompanied by limestone, appear to form the
foundation of the whole islet. A continuous bed of trap overlies the
whole, and reaches on almost all sides to the sea, but it wants such
distinctive properties as would rank it with any of the ordinary
subspecies of trap, being intermediate between basalt and greenstone,
and consisting of an indurated clay-stone highly charged with
protoxide of iron. Pladda is conspicuous chiefly for its lighthouse,
erected in 1790. It exhibits two fixed lights, one above the other:
the elevation of the one light being 130 feet, and of the other 77
feet above high water; and the lights are respectively visible at the
distance of 15 and of 12 miles, from north-east by east, round by the
south, to north-west by west. The bearings from the lighthouse, as
taken by compass, are, the entrance of Campbelltown-bay W. N. W., ¼ N.
distant 18 miles; island of Sanda W., distant 20 miles; Ailsa Craig,
S. W. by S., distant 15 miles; entrance to Loch-Ryan, S. S. W.,
distant 25 miles ; and the Heads of Ayr, S. S. E., distant 16 miles.
The expense of maintaining the lighthouse, for the year 1840, was
£683. In the sound of Pladda, at the south end of Arran, the charts
have 4 fathoms marked, whilst there is a bridge of rock, with 2, 3,
and 4 feet only of water, nearly right across, not justifying any
vessel attempting the passage.
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