ABSORPTIVE POWER OF THE SOIL. 351 



&c. This complexity of the mW effectually ])revents au 

 accurate analysis of its zeolitic silicates. 



If further evidence of the existence of zeolitic com- 

 pounds in the soil were needful, it is to be found in con- 

 sidering the analogy of the conditions whiirh there obtain 

 with those under which these compounds are positively 

 known to be formed. 



At Plombieres, in France, the water of a hot spring 

 (temperature, 140" F.) has flowed over and penetrated 

 throuo-h a mass of concrete, composed of bricks and sand- 

 stone laid in lime, which was constructed centuries ago by 

 the Romans. The water contains about nine ten-thou- 

 sandths of solid matter in solution, a quantity so small as 

 not to affect its taste perceptibly. As Daubree has shown 

 {Ann. des Mifies, 5me., Serie, T. XIII, p. 242), the cavi- 

 ties in the masonry frequently exhibit minute but well- 

 defined crystals of various zeolitic minerals, viz, : chaba- 

 site, apophyllite, scolezite, hnrraotome, together with hy- 

 drated silicate of lime. These minerals have been pro- 

 duced by the action of the water upon the bricks and lime 

 of the concrete, and while a high temperature prevails 

 there, which probably has facilitated the crystallization of 

 the minerals, as it certainly has done the chemical altera- 

 tion of the bricks and sandstone, the conditions otherwise 

 are just those of the soil. 



In the soil, we should not expect to find zeolitic com 

 binations crystallized or recognizable to the eye, because the 

 small qu intities of these substances that could be formed 

 there must be distrilmted throughout twenty, fifty, or 

 more times their Aveight of bulky matter, which would 

 mechanically prevent their crystallization or segregation 

 in any form, more especially as the access of water is very 

 abundant ; and the carbonic acid of the surface soil, which 

 powerfully decomposes silicates, would operate antago- 

 nistically to their accumulation. 



