Shingle on the East Coasts of New Zealand. 85 



point, there being an evident tendency to form a long spit 

 entirely across the mouth of the channel, as has occurred a 

 few miles to the north of Harwich. The North Sea, Pilot 

 states that between 1804 and 1826 there was " a narrow 

 seven-fathoms channel close to the walls of Landguard Fort." 

 In 1826, the point advancing, gradually " reduced the avail- 

 able depth into the harbour to 11 feet." About 1845, 

 dredging was commenced; this has increased the depth to 

 17 feet at low- water springs, which was the depth in 1874. 



The point to which the author wishes to draw special 

 attention is that at one time no shingle seems to have crossed 

 the channel. Then, as the depth was reduced, shingle began 

 to give trouble on the south side; and latterly, it would 

 appear from various accounts, the shingle has decreased 

 again. The conclusion forced on one is, that with a depth 

 of 11 feet, some shingle crossed the channel, but that with 

 a depth of 17 feet or 18 feet it does not cross under ordinary 

 circumstances, During heavy weather, some small quantity 

 may be carried across the increased depth. 



It may be interesting to note here that sand has formed a 

 similar spit, called Spurn Point, partly across the mouth of 

 the River Humber. The depth at which this material can 

 cross the channel would appear, from the soundings given on 

 the chart, to be from 40 feet to 45 feet. 



These two instances are not conclusive, because the chain 

 of circumstances is not as complete as could be desired; but 

 they help to support the author's arguments. They show 

 that shingle does not cross freely a channel the depth of 

 which exceeds 11 feet or so, and that the lighter the material 

 the greater the depth at which it can travel. It may be 

 remarked here that the shingle on the east coast of England 

 is, by all accounts, smaller than that on the east coast of 

 New Zealand. In this case, the former would be able to 

 travel at a greater depth than the latter. 



