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POPULAR SCIENCE REVIEW. 
THE PLYMOUTH BREAKWATER FORT. 
By S. J. MACKIE, C.E. 
[PLATE LXXII.] 
T O comprehend the nature and value of the Plymouth iron 
fort, its position, extent and nature should be clearly 
defined. Plymouth Sound is a vast open U-shaped natural 
harbour, a little over three miles in length, and about as 
wide at its mouth in a direct line between Penlee Point on 
the west, and Reny Point on the east. At about one-third of 
its area the turbulent waves which roll in from the Atlantic 
are checked by a great breakwater formed of rocks quarried 
from the neighbouring hills, mainly at Oreston. In length, 
the breakwater is about 5,000 feet long, rising up with very 
shelving slopes out of some six to seven fathoms of water (at 
low tide). On the eastern side of the Sound, Staddon Point 
juts out well towards the eastern arm of the breakwater ; but 
on the western side the shore recedes between Perdee and 
Picklecombe into a large bay at Cawsand, forming a consider- 
able expanse of water. The actual deep-draught shipways, of 
more than a thousand feet in width, pass on either hand close 
to the horns of the breakwater, nearly behind the centre of 
which, at a distance of a hundred yards, is placed the iron 
fort, to which this article is devoted. At Picklecombe and at 
Bovisand (the point of Staddon) there are granite casemated 
forts defending the water areas a little way in the rear ; the 
distances of these batteries being each about a mile from it. 
A mile and a half up the Sound is Drake’s Island, and half a 
mile further in the background the heights of Plymouth, also 
fortified, as well as are the entrances to the Hamoaze on the 
one hand, and to the Lairy on the other. The position of the 
breakwater fort is thus a most important one, and it is to be 
regarded as the main defence of the Sound. 
The iron fort is based upon masonry foundations faced with 
ranite, and rising 16 feet 6 inches above high-water spring 
tides. Its walls are set in from the masonry about 3 feet, 
there being thus a clear walk or glacis of that width all round 
