282 EXPERIMENTS ON METAMORPHISM AND 



exceptional peculiarity among rocks in contact with basalt, which 

 characterizes the limestone of Kaisersthul, appears to me to result 

 from the conditions of its formation. This limestone was situated at 

 the bottom of a crater of elevation. Before the last dislocation, un- 

 dergone by the formation, brought the limestone to the surface, it 

 had been subjected, at a certain depth, and consequently under pres- 

 sure, to the action of the hot water with which the basalt itself was 

 saturated, and which also deposited minerals in its numberless cavities. 

 The limestones of Mount Somma, so rich in various minerals, and 

 those of Latium, have been produced, like the Hmestones of Kaiser- 

 stuhl, at points where craters of elevation have been formed. When 

 the beds which hermetrically sealed the spot where these chemical 

 reactions took place gave vent, in breaking, to the agents which pro- 

 duced them, these reactions ceased to take place. But what difference 

 of action can there be, in the case of which we are now speaking, 

 between what passed on the surface and what took place in the depths 

 of the earth ? No other, according to all appearance, than that 

 which is owing to difference of pressure. Let us add, that if the 

 vapor of water which, at a very high temperature, no less than liquid 

 water up to its point of ebullition, fail to produce, in the ordinary 

 experiments on the silicates, results like those which the metamor- 

 phic formations present, it is because something essential is wanting, 

 and everything shows that what is wanting is pressure. 



In fine, we have just seen on what grounds we may rightfully sus- 

 pect the concurrence of heat, water, and pressure, as capable of pro- 

 ducing the principal phenomena of metamorphism. What is wanting 

 is to place ourselves in conditions resembling, as much as possible, 

 those under which nature appears to have acted, and to see whether 

 the reproduction of characteristic minerals would be obtained. Such 

 is the object of a series of experiments which I have undertaken, and 

 of which I am about to give an account. 



CHAPTEPv IV. 



EXPERIMENTS ON THE ACTION OF SUPERHEATED WATER IN THE FORMATION 



OF SILICATES. 



Several of my experiments have been already described in a former 

 memoir.* I have thought proper, however, to reproduce here the 

 principal results which were recorded in my first publication, and to 

 add to them those which I have more lately obtained. Even count- 

 ing for nothing the dangers of explosion, which are often of a vio- 

 lence altogether surprising,! the difficulties of experimenting have 



** Annates des Mines, 5th series, vol. xii, p. 289, 1857 ; Bulletin de la SociM Geologique de 

 France. 2d series, vol. xv, p. 97, 1858. 



f Tubes made of iron of the best quality, having an interior diameter of 0.8 inch and 

 4 inch in thickness, soinetitnes burst. They break in the direction of one of their gene- 

 ratrices, and are thrown into the air with a noise like the report of a cannon. If the iron 



