38 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



through the bed of the Channel, when it was above the level of the 

 sea ; but the action of running water cannot be considered sufficient 

 to have hollowed out troughs of this kind, with no exit or open 

 passage at either end. We should rather wonder that they have not 

 yet been filled up by the deposits that must have been poured into 

 them. Here we have a long narrow cavity (" Hurds Dyke ") sur- 

 rounded by water of the depth of about 30 fathoms up to its sides, 

 and having in its centre a depth of 72 fathoms, or about 240 feet 

 more than its edges. It therefore seems probable, from what we 

 know on the subject, that the remark of Sir Henry De la Beche 

 respecting a similar pit (the '' Silver Pit " off the coast of Lincoln- 

 shii-e) would apply to these, viz. that they were the remains of ancient 

 cracks or fissures in the earth. 



The chemical theory of volcanos, the subterranean solution of 

 felspathic, calcareous, and other rocks by water, and the crumpling 

 of strata* appear to account for the origin of cavities beneath the 

 crust of the earth, and its consequent Assuring. 



From the point first taken, nearly to the south of Dungeness, the 

 line of deepest water takes a north-easterly course to a little 

 above lat. 52*^ N.; a winding course, like that of the English Channel, 

 if observed only for a short distance, but in long distances deviating 

 not much from a straight one. From the point last mentioned, in 

 lat. 52° N., the line appears to turn in a direction somewhat to the 

 west of the north ; but beyond this it rapidly becomes shallower, 

 indeed below 30 fathoms. It may be traced, however, with a depth 

 of between 20 and 30 fathoms to a little north of lat. 53° N., and 

 there ceases as a continuous line, though there are detached pits, 

 such as the " Silver Pit " above alluded to, with a depth of from 40 

 to 50 fathoms. But, generally speaking, a bank here runs across the 

 Channel all the way from England to Holland, so that a rise of 20 

 fathoms (120 feet) in the bed of the sea would enable us to walk 

 across to Holland dryshod, all the way from the Wash to the Elbe. 



As the line of deepest water has now terminated in this locality, 

 we must turn to another, and endeavour to recover it. To the north- 

 east of the Shetland Isles we meet with the 100 -fathom line, which 

 passes round the western coasts of Scotland and Ireland. North of 

 the Shetlands it takes a bend to the east, and runs in a direction 

 nearly west to east ; then sweeps round to the north, until it termi- 

 nates its course in that direction almost in a point, and then runs 

 away in a south-east direction, following the line of the coast of 

 Norway. But during the short distance that it has run from west to 

 east, it gives ofi^ a deep channel to the south ; so that in an easterly 

 direction from the north point of the Shetlands there is, after passing 

 over the shoal water near the land, a channel of from 80 to 100 

 fathoms in depth, then a bank of from 60 to 70 fathoms, and beyond 

 that the deep channel which runs conformably to the coast of Norway, 

 to the depth of 200 fathoms or more. There is a deficiency of deep- 

 sea soundings from about lat. 60° 30' to 59° 30' ; but the channel we 

 have mentioned, divided from the deep water on the coast of Norway, 

 * See De la Beche, Mem. Geol. Surv. vol. i. p. 237. 



