316 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



sandy loam. In an area from which the uncallow had been re- 

 cently cleared, 15 yards long, and from 3 to 5 yards broad, I 

 found the surface of this bed honeycombed with sand-pipes, which 

 were from 1 to 3 feet deep, and scarcely 2 feet apart. They were 

 connected by furrows running in various directions. 



From the phenomena above recorded as occurring in Norfolk, 

 combined with those which I formerly observed in Kent, it may 

 be concluded, that the surface both of the solid and reconstructed 

 chalk in those counties has been exposed to the action of which 

 sand-pipes are the result ; and this at various epochs, extending 

 from a period prior to the deposit of the sands of the plastic 

 clay, to the close of the period of the stratified drift. 



The phenomena, observable in Norfolk, of the horizontal strata 

 of sand and gravel, superincumbent on the chalk, bending down 

 into the cavities of the larger sand-pipes as they approach those 

 cavities, led Mr. Lyell to attribute these irregularities to the 

 gradual removal of the chalk after the sand and gravel had been 

 deposited ; and the agent by which he supposed the chalk to have 

 been removed, was acidulated water, percolating the overlying 

 deposits, which deposits subsided into the hollows beneath, on 

 their losing their support. 



That a certain amount of subsidence has, in many instances, 

 taken place, I am by no means disposed to deny ; and we have 

 evidence of this in the vertical strise which I have often observed 

 on the walls of pipes, and which I find, from the paper of Mr. Rose 

 on the geology of West Norfolk, that he has also noticed. The 

 faulted state of the bands of sand and clay at Thorpe, represented 

 in Diagram 6. (supposing that fault to be attributable to some 

 . neighbouring sand-pipe), may also be adduced in proof of the sub- 

 sidence of the strata into those cavities. 



I believe these cavities to have been formed before the super- 

 incumbent strata were deposited. The shallow circular basins 

 observed on the surface of the chalk at Thorpe and Rackheath, 

 and formerly also in Kent, I consider as incipient pipes. The 

 formation of such hollows in siliceous blocks on the sea-shore, by 

 the rotation of sand and water, I formerly pointed out in my paper 

 on the sand-pipes of Kent. I have also observed minature furrows, 

 and conical and cylindrical cavities, now forming on chalk, by the 

 action of sand and water, on the coast of Norfolk, between high 

 and low water mark. These cylindrical cavities are 2 inches in 

 diameter, and 4 inches in depth. 



I beg to compare the sand-pipes in the chalk with the rock- 

 basins worn in the river-beds of gneiss and granite in Southern 

 India, of which Lieut. Newbold has given an account. (Proceed- 

 ings of the Geol. Soc, vol. iii. p. 702.) These cavities are from 

 4 inches to 4 feet in diameter, and 4 feet deep ; and they are 

 connected one with another by shallow channels. For the further 

 details on this subject, I beg to refer to the abstract of his paper. 



The effect of cavities, when once formed in the bed of a rapid 

 river or tide, is to occasion whirlpools, which set in rotation the 



