

Ch. xxii.] 



THE SILVER PITS AND DOGGER BANK. 



569 



more probable that it indicates the original depth of this 



sediment _ 



paj. yj ^ x w**^ ~ ~ ~ 



down. 



Nevertheless, there are some snbmarine valleys, or long 

 narrow ravines traversing the shallow parts of the German 

 Ocean, which seem to have been due to a tidal current, 

 capable either of scouring out a channel, or of keeping one 

 clear by not allowing it to become the receptacle of matter 

 drifted towards it from the nearest coast. Of this nature is 

 the depression called the Outer Silver Pits, about 60 miles 



Head 



about 40 fathoms, or 240 feet. 



Mississippi 



miles 



bottom, and keep open a channel from 



sometimes 



may 



clear the Silver Pits. Mr. Murray in his memoir 



North I 

 Hewitt 



mouth of the Hum 



ber, have been scooped out by the tidal current, whereas the 

 great shoals north and south of the Silver Pits are areas in 

 which drift matter and comminuted shells are constantly 



>arativelv tranquil water. The great shoal 



com 



mi 



. w«~«~-w — CD CD 



Northumberland, is no less than 200 miles 



diameter ; it has been com 



^ _ Wales. In this area there is one tract 75 miles 



long and 20 broad, nowhere exceeding 1 5 fathoms in depth, 



while the shallowest 



Hewitt 



to he only 42 feet under water, and in one place the wreck 

 of a ship had cansed it to be still shallower. South of the 

 Silver Pits there is another vast area of shoals, which we 

 may safely regard as the receptacle both of sediment brought 

 down bv rivers and of matter derived from the waste of the 



Entire as well as broken shells are dredged 

 up on the Dogger and other banks over which fishermen 

 annually trawl their nets . Currents running " A ^" 



British coast. 



sometimes from 



sometimes from the south, remove 



