PLYMOUTH SOUND: ITS TIDAL CURRENTS. ha 
greatly altered the aspect of this locality. Old maps show Ply- 
mouth a much more insular place than it is at present, and also the 
creeks to be much more extensive.* Evidence on this was found 
when in excavating, now many years ago, for the foundations of a 
house in Union Street, near the boundary between Plymouth and © 
Stonehouse, a full-sized anchor and part of a cable were discovered 
several feet underground. The inevitable silting process is no doubt 
going on in the Sound, but at a very slow rate indeed. The immense 
area of mud bottom, quite two-thirds of the outer area of the 
Sound, testifies to it; and Mr. Rennie, subsequently Sir John 
Rennie, in his report advising the construction of the present 
Breakwater, dated 21st April, 1806, says: ‘‘ From conversing with 
pilots and various other intelligent men whom we met at Ply- 
mouth, we have reason to believe that the depth of water in the 
Sound is on the decrease.” 
The silting-up of the Sound had long been a matter of con- 
siderable anxiety in Sir John Rennie’s time; indeed much more so 
than at present. Several Acts were passed forbidding vessels from 
discharging ballast into its waters, and all mining operations which 
affected the washing down of gravel and sand. The earliest are 
dated the twenty-third and twenty-seventh years of the reign of 
Henry VIII., and the sixteenth year of the reign of Queen 
Elizabeth. Sir John Rennie, dealing with the question of silting- 
up, in his report says: ‘‘ And as a sufticient passage’’ (on the con- 
struction of his proposed breakwater, the existing one) “will be 
left for the tide to flow into and out of the Sound at the western 
and eastern ends of the great breakwater, its direction will not be 
turned from the anchoring ground; and no further deposition of silt 
or mud will take place there than does in its present state, except 
indeed immediately without and within the Breakwater itself.”’ 
These predictions have been realized as to the silting-up, imme- 
diately without and within the Breakwater itself, which continued 
increasing for two or three years after its completion, but which is 
now reported to be perfectly stable. No silting-up has been 
detected as yet over the anchoring ground, although there must be 
a decrease in the depth by a small amount, which ordinary sound- 
ings would not show. + 
* Mr. Brooking Rowe, in his paper on ‘“‘ Plympton Castle,”’ pp. 246, 247, 
253, gives singularly clear evidence on the change which has taken place in 
the Plympton valley. 
+ Captain Osborne, R.N., on this point remarks, in a letter dated 23rd 
WOT a Vels dt 
