424 Reviews — A. Daubree' s Experimental Geology. 



M. Daubree illustrates these by a series of cuts with much exacti- 

 tude. Some 20 kilogrammes of bronze coins were found at the 

 bottom of a Roman well (puisard), associated with black organic 

 mud, where they had been bathed for sixteen centuries by mineral 

 waters at present containing 8 grammes of solid matter to the litre, 

 and having a temperature of 68° C. at the principal point of dis- 

 charge. In a permeable bed towards the bottom were evidences of 

 bronze coins, etc., which had undergone decomposition, more or 

 less complete. Four species of cupric sulphide result. The tin 

 appears as a white earthy crust, consisting chiefly of oxide. The 

 lead pipes in places were coated with phosgenite (carbonate of 

 lead and chloride of lead), which, by the reducing action of organic 

 matter in the presence of gypsum, has yielded small but definite 

 crystals of galena. 



Such an automatic laboratory, containing within itself a sort of 

 electro-chemical apparatus, was a valuable legacy of the Romanized 

 Gaul to his descendants, not to be appraised so much for its metallic 

 worth, as for its utility in supplementing those essays in synthesis 

 which the shortness of human life too often forbids to be accom- 

 plished within the limits assigned to one generation. We also learn 

 in this case how Nature is gradually reversing the operations 

 of man ; remarrying, as it were, those elements which had been 

 divorced by the laborious operations of the miner and the smelter. 



It is just possible that discoveries such as the preceding, confirm- 

 ing our knowledge of what can be done in the wet way in warm 

 springs and mine-waters within periods short in a geological sense, 

 may tend to exaggerate the importance of the part played by water 

 as a solvent at a time when the great sulphuretted lodes received the 

 bulk of their metallic charge. These phenomena merely represent 

 the final stages of processes infinitely more energetic. M. Daubree 

 asks, What should we see if it were possible to descend the fractures 

 serving as channels for the ascent of the thermal waters ? We 

 should probably find additional proof of the important modifications 

 produced by water at increasing temperatures, but this would not 

 lessen the probability that the metals associated with lead have 

 been volatilized from depths where no water is in combination with 

 sulphur, selenium, tellurium, or arsenic, just as he has shown how 

 tin has been volatilized in combination with fluorine. 



The second portion of the chemical and physical subdivision of 

 the subject treats of the metamorphic and eruptive roelcs and of the 

 application of the experimental method to their study. The author 

 interprets the word ' metamorphism ' in its widest and most conven- 

 tional sense, 1st, as simple molecular re-arrangement, 2nd, as crys- 

 talline re-arrangement based on matter already on the spot, 3rd, as 

 crystalline re-arrangement with importation of new or elimination of 

 old matter. 



Metamorphism of juxtaposition is the term he prefers for those 

 modifications which are effected by invading rocks within moderate 

 distances, though such modifications may reach as far as 3000 metres 

 in the case of granitic invasions. In dealing with regional metamor- 



