REVIEWS 3 2 3 



quelque lumiere sur la question de la solidification des roches dans la 

 nature. lis peuvent nous faire comprendre pourquoi, en general, les 

 roches les plus solides et les plus compactes sont aussi les 'plus anci- 

 ennes, et ils peuvent nous expliquer la presence de ces milliards de 

 cristaux microscopiques que Ton a observes dans certaines roches, par 

 exemple dans les phyllades, cristaux qui paraissent s'etre developpes 

 meme apres le depot des alluvions necessaires a la formation de ces 

 masses neptuiennes." 



And again : "Cette observation ne me parait pas sans consequence 

 pour certaines theories petrographiques. En effet. s'il est deja pos- 

 sible d'observer un changement d'etat physique dans un agglomerat 

 apres onze annees d'exposition a la temperature ordinaire, il est permis 

 de penser que nombre de phenomenes de crystallization, voire de 

 formation de numeraux, dans les roches agglomerees par la pression, 

 aux depens de matieres a l'etat solide, sans qu'il soit absolument neces- 

 saire de faire entrevenir Taction de dissolvants quelconques." 



He has also 1 experimented with the compression of dampened 

 powders and finds in general that the insoluble bodies, such as metal fil- 

 ings, etc., do not solidify in the presence of water because the water 

 prevents close contact. Soluble substances act differently — bodies 

 whose solution takes less volume than the water and substance solidify 

 more completely than in the dry state, while those whose solution is 

 attended with an expansion of volume consolidate much better in the 

 dry state. The explanation offered is that when the substance is more 

 soluble under pressure, as pressure is relieved some of the material is 

 precipitated into the interstices of the mass and it is solidified, while 

 in the second case some of the matter is dissolved after the relief of 

 the pressure, leaving a porous incoherent mass. 



M. Le Chattilier 2 has noted this same fact that certain bodies in 

 the presence of their saturated solutions solidify under pressure, and 

 explains it a little more in detail as a case of equilibrium under 

 heterogeneous pressure. The water is squeezed out of the mass and 

 therefore is not under so great a pressure as the solid, therefore the 

 solution next to the surface of the solid is supersaturated in respect to 

 that farther away. This water then moving away from the solid pre- 

 cipitates and solidifies the rock. 



^eits. fur Phys. Chem., 2, p. 532. Uber die Kompression von feuchter Pulver 

 fester Korper und die Formbildung der Gesteine. 

 2 Zeits. fiir Phys. Chem., IX, p. 335. 



