568 Reviews — E. Dauhree — Stibterranean Waters. 



of metamorphism. With respect to contact metamorpliism, it is not 

 qnite clear how far the results, in all cases, have been brought about 

 through the agency of water. Of course, where quartz and numerous 

 anhydrous silicates have been developed in a limestone, which itself 

 has become crystalline in the vicinity of an eruptive rock ; supposing 

 such a limestone to have been a nearly pure calcareous rock originally, 

 the ingredients of so many silicates have in all probability been 

 introduced by the agency of waters which owed their impregnation 

 in part to the eruptive rock itself. In dealing with the far more 

 important subject of regional metamorphism, we gather in the first 

 instance that the author excludes the great fundamental gneisses. 

 Although the subject is very fully treated, it is not easy to assert 

 what part water is considered to have played in producing the results ; 

 undoubtedly heat, pressure, and and chemical solvents are required in 

 addition to mere water. After the admirable experiments detailed in 

 the " Etudes synthetiques," and repeated here with excellent illus- 

 trations, it has been abundantly shown that anhydrous silicates can be 

 produced in the wet way. Perhaps this is even more than is required 

 in some cases, since the phyllades of the Ardennes are largely composed 

 of such hydrous minerals as sericite and chloritoid, or chlorite, in addi- 

 tion to quartz. We have also the general statement (p. 375) that the 

 water enclosed in clays, combined and fixed, has had a "preponderating 

 action in the development of metamorphic phenomena." 



• Lastly, Mens. Daubree considers the light which past and present 

 phenomena are able to throw upon each other. He alludes to the 

 great vertical and horizontal extent over which the course of ancient 

 waters is often discernible. Measured by the standard of historical 

 time, existing hot springs enjoy a great stability, though in general 

 the old thermal springs, which have brought the metallic minerals 

 and their gangues into the veins of so many regions, are now dried 

 up. The relative geological age of ore-deposits is discussed, ranging 

 from the great iron- masses of Scandinavia contemporary with the 

 gneiss, to the Tertiary deposits of Comstock, associated with trachytic 

 greenstone. 



He concludes as follows : — " It is thus that water has played a 

 unique part throughout all time in the earth's crust; aided, it is true, 

 by secondary substances, it has been the chief mineralizer, even for 

 minerals such as quartz and the anhydrous silicates in whose pre- 

 sence it is altogether inactive at temperatures which prevail on the 

 surface of the globe, and whose origin for this reason was for long 

 time considered beyond its influence. 



" However, this does not concern the past merely. There is 

 nothing to prove that operations of this nature are arrested. On the 

 contrary, it is more than probable that, as each day goes by, similar 

 actions are contributing to the formation of new minerals ; but these 

 take place in interior regions which are not accessible to our obser- 

 vations. In descending but a few metres from the surface we find 

 silicates of the family of the zeolites and combinations of sulphides 

 similar to those of metallic veins. Unfortunately we cannot observe 

 the products of reactions which take place of necessity lower down 



