116 On Artesian or Overfiowlng Wells. 



in the vicinity, and which is covered, though at times not im- 

 mediately, by a waterproof clay. The wells, which are not 

 sunk to this, the. London day, give abundance of clear, but 

 mostly very hard, water ; while those which penetrate through 

 the London clay, into the subjacent plastic clay, a formation 

 immediately covering the chalk, and consisting of alternating 

 beds of sand, clay and boulders, yields a very soft and pure 

 water *, which, on piercing this clay, often ascends with such 

 violence, that the workmen have scarcely time to escape f . Here 

 the plastic clay seems to be either the conducting medium, or 

 the reservior of the water yielded by the chalk. Paris is known 

 to be situate in a district whose geognostic relations are almost 

 identical with those of London, and therefore we cannot won- 

 der that there, as well as in many other parts of the north and 

 east of France, Artesian wells may everywhere be sunk ; nor 

 can we doubt of the extension of this very useful discovery %• 

 The soil of Vienna seems also to be well adapted for the pur- 

 pose, as partly appears from a geognostic description of Prevost ||, 

 and partly from tlie details given by Popowitch § of one of these 

 springs in a suburb of Vienna, if new bores do not lead to un- 

 satisfactory results f . In the environs of Modena, Rammazini 



• It contains some carbonate of soda, about 4 grains per quart. — Joum. of 

 Science, vol. xiv. p. 145. 



-|- Conybeare and Philips, Outlines of the Geology of England, &c. pt. i. p. 34. 



+ Most of those which have been bored in the town and its immediate 

 vicinity, remain under the surface of the ground, although they are often 

 several feet above the surface of the Seine and the common wells. Among a 

 considerable number of those which are enumerated by M. Hericart de 

 Thurv, in the Annul, de l" Industrie, t. ii. p. 58, there are several from which 

 the water is projected, at least at first, with great force, and not without 

 dancrer, I'ar above the heads of tlie workmen. This, for instance, was the 

 case with one, which, in the year 1780, was bored in the Vauxhall Gardens, 

 and the level of the water of which has ever since been as high as the sur- 

 face. This water comes from a depth of forty yards; but on account of the 

 Ktoney character of the soil and the consequent ex))ense, they are usually only 

 about half as deep ; and this may perhaps be one of the causes that perma- 

 nent spring-wells have not yet been sunk. 



II Joum. de Physique, t. 91. p. 347, & t. 92. p. 428. 



§ Observations of the Physico-Economical Society of the Palatinate for 1770 

 pt. 2. p, 1G9. 



% Riepl, in an appendix to the German translation of M. Gamier's work, 

 p. 162. 



