FUSION AND ABSORPTION. 729 



duce aqueo-igneous fusion, and that such supposed fused material is the 

 source of molten material for volcanoes." Mallet supposes that the material 

 is mechanically divided so fine that a sufficient amount, of heat is developed 

 by this work and by friction between the particles to fuse the rock. How- 

 ever, he does not tell how fine this must be, although he speaks of reducing 

 a rock to an absolute powder. What is meant by an absolute powder is 

 not apparent, but one might suppose it means a powder the particles of 

 which are of molecular size. 



The conclusions herein contained concerning recrystallization and rock 

 flowage have an important bearing upon the hypothesis of aqueo-igneous 

 fusion. It has appeared that if water be present when the material, as a 

 result of the mechanical subdivision, or for any other cause, reaches the 

 very moderate temperature of 185° C, the adjustment is accomplished 

 mainly by recrystallization, and that fusion is not necessary to account for 

 the plasticity of the rocks. Probably a much higher temperature is required 

 for aqueo-igneous fusion than for recrystallization. Barus has failed to 

 secure aqueo-igneous fusion of the silicates at a temperature of 600° C., 6 

 and at temperatures much lower than this it is certain that recrystallization 

 goes on very rapidly. 



So far as the typical schists and gneisses themselves are concerned, it 

 is certain that they are not the products of aqueo-igneous fusion. They 

 have the peculiar textures and structures characteristic of these rocks. (See 

 pp. 779-783.) Every magma crystallizes according to the laws of magmas, 

 and produces textures and structures which are characteristic of such 

 crystallization. The textures and structures of the two classes of rocks 

 are very different. There is no evidence that the great masses of the 

 magmas are formed by the fusion of the crystallized rocks in consequence 

 of mecb inical action. But it does not follow that various rocks, including 

 the schists and g*neisses, may not be fused by contact with intruded 

 magmas. It has been seen in connection with injection that profound 

 metamorphic effects are produced upon the intruded rocks, the ordinary 

 metamorphic forms being slates, schists, and gneisses. It has been held 

 that the phenomena of pegmatization may be explained by crystallization 



a Mallet, Robert, Volcanic energy; an attempt to develop its true and cosmical relations: Philos. 

 Trans. Royal Soc. London, vol. 163, 1874, pp. 147-227. 



& Powell, J. W., Report of the Director: Fourteenth Ann. Rept. U. S. Geol. Survey, pt. 1, 1893, 

 pp. 161-162. 



