45 



and pebbles caught in the ■wliirlpool constitute a drilling machine of 

 great potency. Swallow-holes may in this manuci- be I'ormed. 

 The t'onnalioii of a blow-well may bo acconntcd for by supposing 

 that a bed of clay or other impervious stratum exists under the 

 chalk or limestone rock, only in certain places ])ermitting the 

 water to act chemically on the limestone above it, and thus liaving 

 been formed into a cylindrical column of water, it pierces its Avay 

 like a fountain jet through the beds above it, meclianically and 

 chemically removing from them their natural cement of carbonate 

 of lime or alumina until they in many instances assume tlie form 

 of quicksands. The spring in a stream under the London, Chat- 

 liam, and Dover Ixailway viaduct, known by the name of the 

 Silver Hole, lias probably gained its name from producing in this 

 manner tlic fine white silver-sand at its bottom. But neither of 

 these modes by which water acts is necessary to produce such 

 pits as those in Bigberry Wood or at Wingham ; a subterranean 

 stream is quite sufficient for the purpose. The beds of loam being 

 of a homogenous nature the falling in of material from above takes 

 place e([ually ou all sides, so that the hole is n^ore or less cylindrical ; 

 in some cases remarkably so. There are two instances where such 

 holes liave been produced artificially in the field below the Canter- 

 bury Union, and just above the chalk pit, where two tunnels driven 

 from the face of the chalk have fallen in, producing in one case u 

 circular pit, the other being of irregular form, but ueither conform- 

 ing to tlic elongated shape of the tunnel underneath. "When an 

 underground stream occurs it plays the part of a carrier of the 

 loose material that falls from above, brought down by the trickling 

 of water very ottcn through a hole caused by the root of a tree, 

 roots sometimes running flown many feet to reach a moist stratum, 

 and decaying ou the death of the tree. A natural duct is tluis 

 formed for the surface water, which spreading out by capillary 

 action, as it sinks lower causes a dome-shaped cavity in some in- 

 stances to be formed ; this suddenly giving way would account for 

 such openings as that which occurred at Wingham in a few hours. 

 So that such underground streams play the necessary part of re- 

 moving the particles, as they fall in, and without the presence of 

 whicli openings of the kind could not exist. Besides such natural 

 pits, theie aie a number of circular ones in the district known as 

 dra'w-wclls sunk for obtaining chalk for agricultural purposes. 

 These being sometimes situiited in woods and overgrown by 

 brambles and underwood, form dangeious traps for unwary 

 naturalists. People have in many instances fallen down them, and 

 I am indebted to our i^ssistant-Secretary, Mr. Fullagar, for the 

 following narrative respecting a young girl who fell down one near 

 Lenham ■within his recollection, and alter remaining in it for a 

 fortnight, having but the rainwater that trickled down its sides to 

 ([uench her thirst, she was rescued by an old man and a boy, going 



