324 Professor Buckland on Artesian Wells. 



would rise within 60 or 70 feet of the surface, in sufficient 

 quantity to supply these fountains that have been prepared in 

 the assurance of finding water. Other wells had been sunk 

 in various parts of London, some into sheets of water pervad- 

 ing beds of sand and gravel that alternate with plastic clay, 

 others into the still lower beds of chalk. In all these cases 

 the water was forced up, by hydrostatic pressure, to various 

 distances from the surface. At Brentford there were many 

 wells that continually overflowed their orifice, which is a few 

 feet only above the Thames ; — in the London wells the water 

 rises to a less level than in those at Brentford. 



As the largest part of the earth's surface is composed of 

 stratified rocks, the most frequent cause of water being sup- 

 plied to wells, and springs, and rivers, was the alternation of 

 beds of clay with porous and permeable beds of stone or 

 sand. These alternating strata, having been originally formed 

 in nearly horizontal positions, have been more or less dis- 

 placed, and set on edge by volcanic forces, which raised them 

 from the bottom of the sea. The greater part of these strata 

 being porous and permeable by water, whilst beds of clay are 

 impervious to that fluid, the residuary portions of rain-water 

 (which are not disposed of by floods, or by evaporation, or by 

 entering the bodies of animals or vegetables) are absorbed 

 into the fissures and small interstices of the permeable strata, 

 where they form subterraneous sheets or reservoirs of water 

 for the sustentation of springs and rivers. About two-thirds 

 of the habitable portions of the earth consist of stratified 

 rocks, and the other third part of unstratified and crystalline 

 rocks, such as granite, porphyry, lava, and other rocks of 

 igneous origin. These also contain water in the countless 

 cracks and interstices of their lower regions, and are inter- 

 sected by innumerable fissures, which collect and transmit 

 rain-water, and give origin to springs. 



As persons who have no experience in such subjects may 

 be surprised at the knowledge geologists profess to have ac- 

 quired respecting the internal structure of the earth, he 

 would endeavour to confirm the above theoretical explanation 

 of the origin and supply of springs, by appealing to practical 

 proofs, in the proceedings of water companies and well-dig- 



