Revieics — A. Daubree s Experimental Geology. 427 



word ' metamorphism ' in the sense used by M. Daubree, it will 

 become more difficult than ever to distinguish between altered and 

 erupted masses when viewed merely under their petrological aspects. 



Not the least interesting of M. Daubree's experiments was made 

 with a view to determine how far the capillary infiltration of water 

 could supply the immense quantities used in volcanic eruptions. A 

 suitable apparatus, figured p. 238, enabled the author to demonstrate 

 that liquid water will force its way through a slab of close sand- 

 stone against a very considerable pressure of steam. He therefore 

 infers, that in spite of the powerful upward pressure of aqueous 

 vapour, the cooler waters of the Earth's surface do find their way 

 through the rocks themselves, and that what is known as quarry 

 water is nothing but this feeder surprised at the commencement of 

 its downward journey. 



The second section of the work, being devoted to mechanical 

 phenomena, is worthy of a separate notice, but there are some 

 subjects discussed which have a chemical bearing. Important ex- 

 periments were carried on with a view to ascertain how far the 

 decomposition of silicates is effected by mechanical causes. There 

 is probably no question in the whole work which has a more im- 

 portant geological bearing than this, because it enables us to form 

 some idea how the debris of crystalline rocks is chemically altered 

 during the process of degradation. Dr. Sterry Hunt has always 

 emphasized this point, and those who question the wholesale intro- 

 duction of fresh matter into rocks which the ultra-metamorphic 

 school have taught, attach much weight to their chemical composi- 

 tion as controlling the possibilities of alteration. 



Orthose in fragments was rotated in a cylinder along with dis- 

 tilled water. When the experiment was performed in an iron 

 cylinder, 3 kilogrammes of felspar, after a journey equal to 460 

 kilometres, yielded to 5 litres of water 12^ grammes of potash, 

 with very small quantities of silica and alumina. To effect such a 

 decomposition mechanical division and the solvent action of water 

 must be exercised simultaneously. Curiously enough the presence 

 of chloride of sodium arrests the decomposition. The presence of 

 carbonic acid facilitates the solution, and much silica, as well as 

 potash, is dissolved. Obsidian and leucite are but slightly attacked. 

 In these operations the mud obtained is in such a fine state of divi- 

 sion as to render the liquid opaline, and it takes some days to settle : 

 the quantity of potash retained is still very considerable. Such a 

 substance would form the " phyllades " or argillaceous schists which 

 occur in the stratified terranes at different geological stages : these 

 often contain from 6 to 7 per cent, of potash. 



Finally, M. Daubree once more returns to the subject of metamor- 

 phism, and having observed that dry clay triturated against itself, 

 had its temperature raised in three-quarters of an hour from 18° C. 

 to 40° C, speculates on the possibility of the transformation of 

 mechanical force into heat in regions such as the Alps, during the 

 period when those forces acted with the greatest intensity. W. H. H. 



