Invasion to Regional Metamorphism. 1T7 



work of contact metamorpMsm and of primary ore depo- 

 sition as juvenile in origin — making their way for the 

 first time toward the surface of the earth. 



The waters which serve as the agents for the recrystal- 

 lization taking place in the anamorphism of sedimentary 

 formations must be, however, in part original occlusions ; 

 yet it is doubtful if they alone are competent to serve as 

 agents for the development of schists and gneisses. The 

 changes from mud to shale, from shale to slate and thence 

 to schist show a progressive elimination of the water 

 both of composition and occlusion. A later coarse- 

 grained crystallization, especially if accompanied by 

 fluorinization, suggests the added agency of magmatic 

 waters. 



But waters arising from magmas bring with them the 

 hydrostatic pressure of the greater depths, diminished 

 by their own weight and the f rictional resistances to flow. 

 They thus have an excess pressure above the rocks 

 around them, which is the hydraulic force impelling to 

 further movement. In so far as the specific gravities are 

 concerned, if the water at the point of its elimination 

 has the same pressure as the surrounding rocks, due tO' 

 the depth of cover, then the excess pressure in the fluid 

 tends to increase with vertical distance above the magma. 

 The viscous resistances to flow tend, on the other hand, 

 to reduce the pressure-difference. This excess pressure 

 is favored by the rise of gases through channels rather 

 than by diffusion through rock, since the viscous resist- 

 ances are thereby reduced. From the walls of such 

 channels, diffusion and flow into smaller cracks causes 

 a permeation of the adjacent rocks. Meteoric waters, 

 on the other hand, when flowing downward in channels^ 

 possess a less hydrostatic pressure than exists in the 

 surrounding rocks, because the two are in equilibrium at 

 the surface and the column of water weighs less than 

 the column of rock. Their permeating power is conse- 

 quently diminished and in this respect, as well as because 

 of their lower temperatures, they stand in direct contrast 

 to magmatic emanations. Where whole formations of 

 rocks show, then, that they were permeated through and 

 through with water and carbon dioxide when deep below 

 the surface, there are reasons for regarding such waters 

 as of magmatic origin. Examples are seen in chlorite, 

 serpentine and talc rocks, especially when these are 

 derived from igneous masses, for they may contain over 



Am. Jour. Sci. — Fifth Series, Vol. I, No. 2. — February, 1921. 

 12 



