296 It. A. Daly — Mechanics of Igneous Intrusion. 



The facts of experimental research. — The experiments of 

 Barns, Doelter, Danbree, Delesse, Cossa, Bischof, Oetling, 

 Morozewicz and others show : 



1. That representative natural or artificial silicate mixtures 

 at ordinary atmospheric pressure become thinly molten at a 

 temperature only slightly above that of solidification ; 



2. That, in every instance, a great increase of volume char- 

 acterizes the change from the solid to the liquid state ; 



3. That, with strong probability, this volume increment and 

 resulting density decrement are so far preserved in rock magmas 

 under plutonic conditions as to forbid the flotation of blocks 

 of the average country rock immersed in the average magma 

 in depth (other allied conclusions have been already summa- 

 rized on pages 279 and 280) ; 



4. That the chief rock-forming minerals are soluble in all of 

 the melted silicate mixtures yet investigated, and at the tem- 

 peratures ruling when those mixtures are thinly molten ; 



5. That pressure aids the solubility of minerals indirectly by 

 retaining in the magma, water and other solvents, but retards 

 it, probably in much less degree, by raising the temperature of 

 fusion for silicate minerals. 



6. That there is evidence of differentiation in molten magmas 

 by gravitative effect. 



The tests of the hypothesis of overhead sloping and enlarge- 

 ment of magma chambers. — Reasons are given for concluding 

 that : 



1. The cause cited for overhead stoping is quantitatively suf- 

 ficient for the majority of stocks and " batholiths." 



2. The presence of foreign inclusions at internal contact 

 belts of stocks and " batholiths," and the detailed phenomena 

 associated with those inclusions, are facts of nature expected 

 on the hypothesis. It is implied that the removal of blocks 

 from the chamber-vault is comparable to the work of a river. 

 The active corrasion of a stream in its youth is rapid and cor- 

 responds to the rapid stoping of an intrusive body in its first 

 long stage of high temperature and fluidity. The feeble cor- 

 rasive power of a stream in its old age corresponds to the 

 diminished stoping activity of the magma in its viscous, solid- 

 ifying period. The conclusion is drawn that, under the ener- 

 getic conditions of high liquidity, a magma may open, in the 

 invaded formation, a chamber of a size appropriate to a stock 

 or " batholith." Independent grounds exist for believing that 

 ample time is allowed by granitic intrusion for such integra- 

 tion of relatively small effects. 



3. The corollary of abyssal assimilation has many experi- 

 mental and other data in its favor and is backed up to a greater 



