UNDERGROUND WATERS. 513 



denote the intervention of this interior water. Thus, in this order 

 of geological phenomena, when we might have believed that heat, 

 accompanied by certain chemical actions, was the sole agent, sub- 

 terranean water has also had its part to play. 



This conclusion regarding the fundamental cause of metamor- 

 phism, although it had been justified by observation, still needed 

 an experimental sanction. For that, the investigator should put 

 himself in circumstances as nearly as possible like those in which 

 Nature seems to have acted, and obtain the reproduction of char- 

 acteristic minerals. I have tried to realize this. The principal 

 difficulty in operating under the enormous pressure acquired by 

 the vapor of water when the temperature approaches the point 

 of dull redness is to find walls capable of resisting it. Water 

 having been placed in a glass tube, which was then sealed by a 

 lamp, this tube was introduced into a second tube of iron, with 

 very thick walls, which was also closed, but not without difficulty, 

 at the forge. In order to counterbalance the tension of the vapor 

 in the interior of the glass tube, which might cause it to burst, 

 care was taken to pour water outside of this tube, between its 

 walls and those of the iron tube. The apparatus was set upon 

 the dome of the furnace of a gas-factory in contact with masonry 

 at a dull-red heat, in a thick bed of sand, where it remained for 

 several weeks. Under these conditions, explosions of extreme vio- 

 lence took place. The most strongly resistant tubes were thrown 

 into the air, bursting with a noise comparable to that of a cannon- 

 shot. It was not possible to multiply the proofs to the extent 

 that was desirable ; but those that were made were sufficient to 

 reveal facts quite different from those which we had deduced in 

 laboratories under ordinary conditions. 



The water acted very energetically upon the glass, which un- 

 derwent a complete transformation, in composition and appear- 

 ance. It was replaced by a white mass, quite opaque, resembling 

 porcelain, with swellings and blisters, the results of softening. 

 There had been developed, at the expense of a part of the sub- 

 stance, numbers of minute crystals, colorless and limpid like 

 rock-crystal, with which they are identical, even to small details 

 in the forms. These artificial crystals appeared, now isolated, 

 now grouped into geodes which it was impossible to distinguish, 

 except for the difference in dimensions, from those of nature. 

 Another product of the same experiments deserves no less atten- 

 tion. It is pyroxene, which appears in little green, brilliant, and 

 transparent crystals, exactly like those of the Alps. For the first 

 time an anhydrous silicate had been seen to be produced by the 

 action of water.* 



* More recently, feldspar has been imitated, under similar processes, by MM. Friedel 

 and Sarrasin. 



VOL. XXXIT. — 33 



