180 J. Barrell — Relations of Subjacent Igneous 



reaction shows by this hydration an increase in volume 

 of 14.3 per cent. 



The writer has recalculated this equation, first taking 

 in the water as part of the volume with density = 1, but 

 not regarding the SCOs or 3K2CO3. Instead of an expan- 

 sion, the result showed a shrinkage consequent upon 

 hydration amounting to 17 per cent. Second, as an 

 extreme condition, the 3CO2 and 31^2^03 were also figured 

 in, the CO2 being assigned a density of 0.17 and the 

 density of solid K2CO3 in the absence of any statement 

 in Watt's Dictionary of Chemistry being arbitrarily 

 assumed as 2.0. This now showed a shrinkage due to 

 hydration and carbonation amounting to 39 per cent. 

 No value is to be attached to this particular equation or * 

 to these exact figures, but they serve to strikingly illus- 

 trate the principle under discussion. 



The rocks are never so impervious as to effectively 

 retain all the magmatic emanations so that that extreme 

 assumption is farther from the truth than the other 

 assumption that the fluids and gases do not enter in any 

 measure into the volume equation. For magmatic 

 emanations the truth must lie between. 



The alteration of basic igneous rocks into amphibolites 

 implies, then, very high temperatures in order that dis- 

 sociation due to temperature may be stronger than the 

 hydration favored by the retention of vapors. The 

 alteration into chlorite and serpentine rocks may also go 

 on at temperatures only less high, provided that they are 

 pervaded under high pressures by abundant magmatic 

 waters. These minerals lose all their water of crystal- 

 lization only at red heat, about 700° to 900 "" C, even in 

 the absence of pressure. It would seem, therefore, as if 

 under conditions where water was freely supplied from 

 below and could only escape more slowly above, hydra- 

 tion could go forward at temperatures approaching red 

 heat, distinctly above the critical temperature of water. 

 The curve of relations between temperature and pressure 

 which control this reaction may possibly be determined 

 by laboratory experiment and is a matter of importance 

 for the interpretations of the conditions of meta- 

 morphism. 



In the light of this reasoning, it appears probable that 

 the regional alteration of the Keewatin lavas into green- 

 stone schists is a mark of pervasive magmatic waters 

 emanating from the Laurentian granites below. 



