Dr. Living — The Makern Crystallines. 459 



a way as to make it probable that, when the deformation began, that 

 mineral was in the colloid state, owing to the concentration in it of 

 the traces of water present in the original magma, as the anhydrous 

 minerals separated out.' This deformation probably occurred when 

 the whole rock mass was still at a fairly high temperature ; and, 

 that the present structure resulted from pressure acting upon a mass, 

 in which the minerals were already differentiated in the manner 

 indicated prior to solidification, and not causing that differentiation, 

 seems the more probable from the fact that traces of residual felspar 

 are often seen in these quartz-veins. It is, at least, as easy to 

 explain the observed facts in this way as to suppose that pressure 

 has brought about a deformation of original felspar, and led to the 

 removal of its bases with the separation-out of quartz. The same 

 sort of flattening-out (in pancake fashion) of the quartz in masses of 

 considerable size (several inches long) was observed in some cases 

 of the more felspathic masses, where the mass, as a whole, has been 

 squeezed into a dyke-like form. A notable example of this was 

 seen in the Dingle Quarry at West Malvern. 



[The retention at high temperatures of the water of hydrated silica 

 by sufficient pressure acting hydrostatically is only another example 

 of the same principle as we have learned to recognize in the fusion 

 of limestone, without dissociation of the COg from the CaO, as a 

 necessary stage of marmorization. If P represent the pressure 

 required to prevent dehydration of colloid silica or dissociation of 

 Ca CO3 in any given case (at high temperature), it is easy to see that 

 P may be the sum of — 



the pressure due to its depth in the lithosphere (pi), 

 the pressure due to the depth of the hydrosphere, if any (p.2), and 

 the pressure due to the supernatant atmosphere (pg). 

 The equation P := pi -|- pj + pj is therefore true in all cases ; but 

 with recession in time pj and pj would merge into one another, 

 P2 diminishing, and pj increasing, as we approached the " pre-oceanic " 

 conditions of early Archaean time in the history of the lithosphere, 

 and even so much of pi being added to the compound hydro- 

 atmospheric term, that the depth in the lithosphere necessary to 

 furnish P would not be very great. That is to say, the requisite 

 pressure might be found at or near the surface of the lithosphere. 



• ^ The author has discussed this fluxing- action of traces of HoO (and perhaps other 

 oxides) elsewhere. (See "Met. of Eocks," pp, 48-50,- also p. 86, where the case 

 of quartz in granite is considered.) It may be as well to remind geologists that 

 " fluxing-action " may display itself in retarding congelation of mineral matter as the 

 temperature of a liquid or viscous mass falls, just as much as in hastening the fusion 

 of a solid mass. These are only two aspects of the same law. The proportions in 

 which SiOa may hold H2O in combination, extend over a very wide range ; and it is 

 almost certain that the critical temperature of hydrated silica is lowered in some 

 proportionate relation to the amount of H,0 present. Compare the results of the 

 Author's own experiments, given in App. i. note C of his original thesis put forward 

 in January, 1888 (p. 100 of the published work). It is possible that slight hydration 

 of Si03 at depths might exist even at a red heat, pressure preventing the escape of 

 water (as in Dr. KroutschofE's recent experiments). Dr. Callaway has come near 

 the idea on p. 500 of vol. xlv. of Q.J.G.S., though he seems to mistake this fluxing 

 action of water for "solution." 



