296 Prof. F. Lmcinson-Lessing — Origin of the Igneous Rocks. 



that in 'younger periods the re-melted parts of the crust were more 

 complicated on account of assimilation and differentiation, we must 

 admit that the number of marginal and local facies and of subordinate 

 rare rock-types will increase as we pass from the older periods to the 

 younger. 



The hypothesis that the earth's crust has been subject to melting 

 and refusion has been advocated by geologists, beginning with 

 Hutton, who maintained more than a hundred years ago (in 1788) 

 that the sedimentary materials are metamorphosed and even partly 

 melted, being in this way transformed into eruptive rocks when 

 they come into deeper parts of the crust. During the past few years 

 this conception has been largely developed in the studies of Sederholm l 

 on the crystalline schists, and in the work of Lukaschewitch, 2 who 

 discerns in sedimentation, subsidence into the deeper parts of the 

 crust, metamorphism, melting, eruptiou, weathering, and sedimentation, 

 a complete cycle. It is not my purpose to give here an account of 

 the literature on refusion of the crust, but a few examples of such 

 views amongst modern geologists may be cited. 



In his well-known Karlsbad discourse Suess has expressed his 

 opinion that the eruptive rocks do not come from a central liquid 

 nucleus, but that they originated by melting of the crust under the 

 influence of ascending hot gases. In the last part of his Antlii% der 

 Erde the hypothesis of refusion (Aufschmekung) is developed in the 

 chapter "Die Tiefen". 



Branca 3 also supports this hypothesis, although he would restrict 

 the melting to the deeper parts of the crust, the sedimentary rocks 

 not undergoing fusion. Haug's 4 opinion is that sediments are melted 

 in sinking geosynclines ; he thinks nevertheless that the presence of 

 alkalies in the eruptive rocks could not be explained in this way, and 

 that it is necessary to admit also a fluid pyrosphere. Haug's views 

 on granite have already been cited. As to his doubts concerning the 

 alkalies, they cease to apply if we assume, as I have done, that the 

 refusion process attacks not only the parts of the crust composed of 

 sediments but also those' which are formed by eruptives. Haug's 

 conclusion that it is necessary to admit a fluid pyrosphere is also not 

 the only possible hypothesis, as separate magmatic basins would explain 

 equally well the peculiarities of igneous rocks. 



Dolomieu 5 expressed a similar view when he supposed that trachyte 

 was a re-melted granite, because he found granitic enclosures in the 

 trachyte of the Puy de Dome. Dutton 6 and Schwarz 7 have also 

 considered lavas as re-melted parts of the crust ; and very close to 

 the theory of re-melting are the ideas of Delesse 8 and Sterry 



1 J. Sederholm, " Om Granit och Gneiss": Bull. Comm. Geol. Finlande, 

 No. 23, 1907. 



2 0. Lukaschewitch, The Inorganic Life of the Earth. Part II, The Life of 

 the Rocks. St. Petersburg, 1909. 



s Branca, Centralbl.f. Mineral, 1909, p. 135. 



4 E. Haug, Traite de Geologic. 



5 Cited by Lacroix, Mont Pelie, ii, p. 56. 



6 Dutton, The High Plateaux of Utah, 1880, p. 125. 



7 E. Schwarz, " Hot Springs" : Geol. Mag., 1907, No. 480, p. 258. 



8 Delesse, Etudes sur le metamorphisme , 1862, pp. 157-220. 



