Notices of Memoirs — 7 he Suh-Wealden Exploration. 261 



the surface is visibly sinking; the docks have already gone down 

 about ten feet, and the bridge over the river Weaver has again to be 

 raised. In the intermediate parts of the valley the whole surface is 

 being submerged, fomiing a mere called " Tlie Flashes," and, as the 

 navigation follows the valley, " it is evident," says Mr. Dickinson, 

 " from the surface level being at a considerably less elevation above 

 sea level than the thickness of rock-salt underneath, the subsidence 

 now so actively begun at Northwich and Winsford may end in the 

 whole of this portion of Cheshire being submerged." That this 

 danger is a serious one may be inferred from the fact that the 

 thickness of the salt deposit at Northwich is 180, and at Winsford 

 210 feet ; whilst the elevation of the surface at the former place is 

 only 20 feet, and at the latter place about 40 feet above the sea level ; 

 but it is hard to say what measures can be taken to avert what would 

 be a national calamity. 



Mr. Dickinson refers to the probability that the contortions 

 observed in strata overlying the saliferous rocks in places where salt 

 is not now known to exist, may be due to the former presence of 

 that mineral, and its having been dissolved and carried away — as, 

 for instance, near Nottingham, in the Lias quarries at Newbold near 

 Eugby, and other places ; and he remarks that, although it would 

 be premature to affirm that rock-salt has existed along the entire 

 range of the red marls from Eugby to the Cleveland district in 

 Yorkshire, it is possible that this has been the case, and that many 

 of the landslips which have occurred upon that range may have 

 been due to its removal.' J. M. 



T 



I.— The Sub-Wealden Exploration. 



HE boring to prove the Palaeozoic rocks of Sussex, which was 

 X commenced in 1872, is now being carried on with great vigour. 

 The adoption of the Diamond method of boring has proved a great 

 siTOcess. Mr. Henry Willett, in his Sixth Quarterly Eeport, dated 

 March 28th, states that a total depth of 6-71 feet has been reached. 

 The drill, called the " Crown," is a ring of soft steel 3^ inches iu 

 diameter, and has 15 diamonds set in it round its lower edge. It 

 revolves at a speed varying from 150 turns a minute in soft strata, to 

 300 in hard rock. Water is pumped down the centre, and rising at 

 the sides, conveys the debris in suspension to the surface. The 

 diamonds are not brilliant, and have no cleavage planes ; they come 

 from Brazil, and are called "Carbonado." The cores brought up are 

 sometiines six or seven feet long in one piece, and form a beautiful 

 section of all the strata passed through. The fact that delicate shells 

 are found lying at right angles to the axis of the bore, is an indisput- 

 able proof that the beds are horizontaL 



1 As bearing upon this subject, -^^6 would refer to a paper by the Kev. J. S. Tute 

 "On Certain Natural Pits in the Neighbourhood of Ripon," Geol. Mag. 1868, 

 Vol. V. p. 178.— Edit. Geol. Mag. 



