48 R. A. Daly — Mechanics of Igneous Intrusion. 



than one per cent of its own weight in volatile matter directly 

 derived from the earth's interior. 



It follows that an enormous amount of water, carbon diox- 

 ide and carbon and sulphur compounds may be given off each 

 time that geosynclinal sediments have been assimilated by 

 molten and then crystallized magma. From each cubic kilo- 

 meter of assimilated sediments about six per cent by weight 

 of liquids and gases must be dissolved in the syntectic magma 

 and, as crystallization proceeds, a large part of this fluid must 

 be expelled. 



In less important degree we may expect that the remelting 

 or solution of an igneous rock by an intrusive magma should 

 cause the evolution of some of the fluid matter which had 

 been, as it were, frozen into the solid rock. Lincoln has aptly 

 called such fluids " repressed emanations."* Gautier's and 

 Brun's experiments show that many and probably all igneous 

 rocks give off gases on being highly heated. f Reheating 

 after cooling causes the renewed emanation of gases. Volatile 

 matter trapped in crystallized secondary granite may thus be 

 driven off, if that granite be dissolved in a younger molten 

 magma with subsequent crystallization of the syntectic. 



The stoping hypothesis in its broadest statement demands, 

 therefore, that post-Archean, batholithic granites, syenites and 

 diorites should be accompanied by special evidences of fluid 

 emanations. 



These fluids were deposited and buried in the strata. They 

 have been resurrected in their activity. They have u risen 

 again", both literally and figuratively ; they may be called 

 " resurgent" emanations. The " repressed" emanations of 

 secondary igneous rocks may similarly be liberated by the 

 distilling action of younger magma ; as these fluids become 

 revivified in their geological activities they may be regarded 

 as forming a second kind of "resurgent" emanations. All 

 " resurgent" emanations are of secondary origin and, therefore, 

 stand in contrast to " juvenile" emanations, namely, those 

 which, for the first time, have issued from the earth's interior 

 and become geologically active on or near the surface. Mag- 

 matic emanations are, apparently, divisible into two great 

 classes, both of which should be recognized in complete discus- 

 sions of ore-deposits. 



That the stoping hypothesis stands this further test seems to 

 the writer entirely clear. The prevalence of quartz veins and 

 pegmatites in the walls and roofs of actual granitic, syenitic, 

 and dioritic stocks and batholiths, and the intensity of the 

 contact-metamorphism produced by the intrusions of, and 

 especially the emanations from, these rocks are facts as famil- 



*F. C. Lincoln, Economic Geology, ii, p. 268, 1907. 



+ A. Brun, Archives des Sciences Phys. et nat. Geneva, May and June, 

 1905 and November, 1906 ; A. Gautier, Annales des Mines (6), ix, p. 316, 

 1906, and Econ. Geol., i, p. 688, 1906. 



