SUBTERRANEAN RIVERS AND CURRENTS, 



303 



nean heat. This agent may, perhaps, have been, in some manner, 

 the cause of the formation of the cavern ; it is, however, supposed, 

 by some, to have been an excavation formed at a remote period by 

 mining operations. 



Instances of rivers of considerable magnitude sinking into the 

 earth, and emerging again at the distance of several miles, have been 

 long known in many countries : it is not the object of the present 

 chapter to enumerate them, but to direct attention to these subter- 

 ranean streams, that have no apparent connection with the surface. 

 It cannot be doubted, however, that the rivers which run only for a 

 few miles under ground, and emerge without any apparent loss of 

 water, must effect considerable changes in the strata during their sub- 

 terranean course. In some cases rivers are absorbed into caverns, in 

 others they merely sink into softer strata, as takes place with the 

 river Rhone, about twenty miles from Geneva, at what is called the 

 Ferte du Rhone. See Travels in the Tarentaise, vol. ii. p. 264. 



The subject of subterranean currents has scarcely attracted the 

 attention of English geologists, but it is beginning to excite enquiry 

 in France, where the practice of boring for water is becoming gen- 

 eral, and has brought to light some interesting facts. In the report 

 of M. Desnoyers, before referred to, several of these facts are de- 

 scribed, but he previously states the observations of MM. Boblet and 

 Virlet, on the closed valleys or gulfs in central Morea, called katavo- 

 trons, " into which torrents of water amassed during rainy seasons 

 are precipitated, carrying with them the mud with which they are 

 coloured, the skeletons of animals, with fragments of shells and plants 

 mixed with gravel, which they introduce into subterranean cavities. 

 The water again springs up at a great distance from the sea, pure 

 and limpid. This circumstance serves to explain the filling of many 

 caverns ; may it not also explain the sinuous passages filled with 

 sand and gravel, between strata which are found at great depths from 

 the surface in the environs of Paris ?" 



From the borings and sinking for water in different parts of FrancCj 

 it is evident that they occasionally meet with considerable subterra- 

 nean streams that have somewhere a connection with the surface wa- 

 ters. In a well sunk at Tours, in 1829, in the lower chalk, to the 

 depth of 330 feet, the water rose rapidly for some hours, bringing 

 with it much fine sand, fragments of thorns and seeds of marsh plants, 

 with land and freshwater shells unchanged. Another fact was re- 

 cently discovered at Reinke, near Bochum, in Westphalia, A well 

 was sunk to the depth of a hundred and forty-three feet, when the 

 water rose to near the surface, bringing with it small fish from three 

 to four inches in length. The nearest currents of surface water are 

 from two to five leagues distant from the well. How small is the 

 proportion of seeds, shells, or fish, sand or gravel, that came to the 

 surface, compared with those which are arrested in their progress,, 

 and finally fill up the subterranean passages and change the direc-- 



