ABSORPTIVE POWER OF THE SOIL. 351 
&c. This complexity of the soil effectually prevents an 
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 which 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 
through 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 Daubrée has shown 
(Ann. des Mines, 5me., Série, 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, harmotome, 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 quantities of these substances that could be formed 
there must be distributed throughout twenty, fifty, or 
more times their weight 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, 
