April lo, 1890] 



NATURE 



541 



outlet for the River Crouch. It will therefore be seen that 

 the Wallet is really only a channel to the Rivers Colne, 

 Blackwater, and Crouch, and is of no importance as a 

 channel towards the Thames. It was last surveyed by 

 Staff-Captain Parsons in 1877, and as its features have 

 not materially changed since 1800, it will probably not be 

 surveyed again for many years, unless the swatchways 

 across the Gunfleet should deepen or others open up of 

 sufficient importance to render the Wallet useful as a 

 traffic channel. There were formerly other swatchways 

 across the Gunfleet, but these are now closed. 



The channel next the Wallet is named the King's 

 Channel, or Swin ; the eastern part is named East 

 Swin,; the central part Middle Swin, and the inner 

 part West Swin. This is the channel through which 

 all the traffic between London and the northern ports 

 of the Kingdom passes, and it is almost always 

 crowded with shipping. The East Swin is bounded at 

 first by the Gunfleet sand to the north-westward and the 

 .Sunk sand to the south-eastward, and is 3 miles wide ; 

 but 8 miles within its entrance two other banks com- 

 mence — one, the IJarrow, being very extensive, upwards 

 of 13 miles in length and 2 in breadth ; and the other, 

 the Middle or Hook sand, a narrow ridge about 6 miles 

 long, extending along the north-west face of the Barrow 

 sand, and leaving a channel nowhere less than r! of a mile 

 wide between them. It will thus be seen that 8 miles 

 within the entrance of the East .Swin it is split up into 

 3 channels ; the northernmost retaining the same name, 

 the channel between the Middle, or Hook sand, and the 

 Barrow being known as the Middle Deep, whilst the 

 channel between the Barrow and Sunk sands is known 

 as the Barrow Deep. The Middle Deep rejoins the Middle 

 .Swin, but the Barrow Deep and West Swin bothriin into 

 what is known as the Warp. The Swin is well buoyed 

 and lighted throughout, but the Middle and Barrow Deeps 

 have not yet been buoyed. In fact, it has hitherto not 

 been necessary to do so, as the least water in the main 

 channel of the Swin has, up to recently, been ample for 

 all that has been required ; but a steady shoaling has 

 been taking place in a critical part of this channel since 

 1800, and it now seems to be only a question of time 

 before the Middle Deep will have to be marked. 



To illustrate the changes in progress here. Plan II. has 

 been constructed, showing the condition of the critical 

 part of the navigation in the Swin each time it has been 

 thoroughly surveyed. By this diagram it will be seen 

 that in 1800 the ruling depth in the channel between 

 Foulness sand and the Middle or Hook sand was 35 feet at 

 low water. Forty-three years later, a bar, on which the 

 depth at low water was 28 feet, had formed between the 

 Foulness sand and the Middle. In 1864 the depth had 

 decreased to 24 feet, and, in 1889, to 21 feet, showing a 

 steady decrease since 1800 of about one foot in every six 

 years. The deposit is of sand, shells, and mud. This is 

 the only shallow part of the Swin ; and as it is evident 

 that, so far as our knowledge extends, we may expect it 

 to continue to decrease in depth, and as even now, with 

 strong south-west winds prevailing in the North Sea, it is 

 by no means rare for the tide to fall 3 feet below the level 

 of low water ordinary springs, so that the depth would be 

 reduced to 18 feet, it is clear that vessels of heavy draught 

 will either have to wait for tide or use another channel. 

 Already our small armoured vessels of war have to time 

 themselves to reach this obstruction by half-tide. For- 

 tunately, the Middle Deep is an alternative channel with 

 ample depth in it, which only requires to be buoyed, and 

 this can readily be done. This Deep seems to be in a 

 better condition now than it has been for 50 years, for, 

 when surveyed by Bullock, in 1843, there was a bar of 

 25 feet at its east end. This had oisappeared when it 

 was surveyed by Calver in 1864, and there was then a 

 channel of two cables in width between the edges of the 

 30 feet contour lines of soundings surrounding the Middle 



sand and Barrow. There is now a channel four cables in 

 width between those contour lines in the narrowest part 

 of the Deep. 



The Barrow Deep, referred to as the third channel 

 branching away from the East Swin, is deep throughout, 

 and without obstruction. It varies somewhat, as shown 

 by the different surveys, but is an excellent highway, 

 which only requires buoying to be available for traffic. At 

 present the London County Council are allowed to empty 

 rubbish in this Deep, which seems rather a pity, as there 

 is no knowing what may be the result eventually, more 

 especially as we have at present no observations to show 

 to what depth the tidal scour is of service. .Any inter- 

 ference with the channels, likely to cause an obstruction, 

 should be avoided. 



The Sunk sand, which is the south-eastern boundary 

 of the Barrow Deep and the north-western boundary of 

 the Black Deep, has undergone great alterations since 

 originally surveyed in 1800. In that year it is shown as 

 a long sand which really extended from the present north- 

 east end in one continuous line of shallow water to the 

 inner end of the Oaze sand, a distance of 26 miles. On 

 it were many dry patches, named Great Sunk, Little 

 Sunk, Middle Sunk, Knock John, &c., and the only pas- 

 sage across was a three-fathoms channel at low water at 

 the eastern end of the Oaze. When surveyed by Bullock, 

 1835-45, this chain of sands had altered very consider- 

 ably, and had several channels or swatchways across it 

 — a swatchway of 22 feet at low water between the Great 

 and Little Sunk smds : a swatchway of 60 feet at low 

 water between the South-West Sunk and the Knock John 

 sands ; a 35'-feet channel i^ mile wide between the Knock 

 John and North Knob sands ; and a swatchway of 26 

 feet between the North Knob and the Oaze. When 

 surveyed by Calver, 1862-64, this series of banks had 

 again altered : the swatchway between the Great and 

 Little Sunk sands had only 12 feet in it at low water; 

 the swatchway between the South-West Sunk and the 

 Knock John had shoaled to 40 feet ; but the channel be- 

 tween the Knock John and North Knob had deepened 

 to 45 feet, and a narrow channel of 40 feet at low water 

 had opened out between the Oaze and North Knob. 



In 1888-89, when surveyed by the Triton, the swatch- 

 way between the Great and Little Sunk sands had en- 

 tirely disappeared ; the swatchway between the South- 

 West Sunk and the Knock John sands had narrowed and 

 shoaled to 29 feet ; the channel between the Knock John 

 and North Knob shoals had decreased to 24 feet, whilst 

 the channel between the North Knob and the Oaze had 

 increased its width to one mile, with about the same 

 depth (viz. 40 feet) at low water. In fact, the chain of 

 sands known as the Sunk, Knock John, Knob, and Oaze, 

 which were, in 1800, one continuous bank, after breaking 

 up into separate patches, again show signs of resuming 

 the form they possessed when originaliy surveyed, the 

 only deep channel across them now being between the 

 Oaze and North Knob. 



The Black Deep is the channel bounded to the north- 

 westward by the chain of sands just described, and to 

 the south-eastward by another chain of sands named 

 Long Sand : Shingles, Girdler, and the flats extending 

 from the Kentish shore. It is a deep-water channel, the 

 inner part of which has been buoyed since 1882, and lighted 

 since December last, as it communicates by a deep-water 

 swatchway, named the Duke of Edinburgh Channel, 

 with the deep water off the North Foreland, and so forms 

 a convenient outlet for the heavy-draught vessels bound 

 southward from the Thames. There seems to be some 

 tendency to shoal in the north-east end of the Black 

 Deep, but it has only once been sounded — viz. by Bullock, 

 in 1843 ; and we have not yet quite completed our examina- 

 tion of it throughout, so that no thorough comparison is 

 yet practicable. 



The chain of sands which bound the south-east side of 



