540 



NATURE 



[April lo, 1890 



Dudgeon light-vessel about one mile from her supposed 

 position, and the Outer Downing hght-vessel nearly two 

 miles from the charted position. 



All these light-vessels are either out of sight of land, or 

 can only be seen from an elevated position on the shore 

 on rare occasions. 



It is therefore naturally the object of the Elder Brethren 

 of the Trinity House to utilize the channels closest to 

 the shore, and, as these channels are also the most direct 

 into the Thames, the northern channel following the 



general trend of the Essex coast, and the southern that 

 of the Kentish coast, no other channels would require 

 marking if the depth in these was sufficient for the traffic. 

 Hitherto the one northern channel has been enough, but 

 this is steadily shoaling, as will be described further on ; 

 but the southern channels are mostly shoal, and one after 

 another has had to be opened up as the size of the vessels 

 and their draught of water increased, until there are now 

 five buoyed channels off the Kentish coast, two of which 

 are lit ; but only one can be termed a deep-water channel, 



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PLAN I. — Thames Estuary. (Depths in Fathoms. ) 



and this would seem to be the very channel which opens 

 and closes periodically, as will be shown subsequently. 

 Should this prove to be the case, there will be intervals 

 during which there will be no deep-water channel into the 

 river on the south side of the estuary. 



By a reference to Plan I., showing, on a small scale, the 

 whole estuary, it will be seen that the northernmost 

 channel, viz. that close to the coast of Essex, is named the 

 Wallet, and that this is separated by a series of banks, 

 termed Buxey and Gunfleet, from the channel next it. 



These banks, which are collectively i8 miles long, are dry 

 for the most part at low water ; there are, however, two 

 narrow passages across them, one separating the Buxey 

 from the Gunfleet, called the Spitway, and the other 

 separating the Buxey from the Dengie flat (extending 

 from the Essex coast). The Spitway, which, when 

 sounded in 1800, had a depth of nine feet, has remained 

 at that depth until recently, but now has only a depth of 

 5 feet at low water ; the channel between the Buxey 

 sand and Dengie flat has about 12 feet, and is merely an 



