378 R.A.DALY MErA-MOHl'lTISM AND ITS PHASES 



Virlet (d^Aonst) — 1847, page 502 — used the expression ^^metamor- 

 phisme normar' to signify the alteration of rocks by interior heat acting 

 at a time when the earth's crust was comparatively thin; he assnmed the 

 alteration to have been aided by pressure, and especially by the presence 

 of water, botli magmatic and connate. Yirlet described "normal meta- 

 morphism" as also '^general." He held that primitive rocks as such can 

 no longer be fonnd at the surface of the glol)e, because they have all been 

 metamorphosed since their original "refroidissement." As indicating his 

 grasp of the im])ortance of solvents in nietamorphism, he wrote that, if 

 original crust rocks were cxev discovered, they must prove to be free from 

 water. Three years before (1844, page 846) Virlet had emphasized the 

 injection theory of gneiss, using tlie expression "roches d'imbibition," a 

 formula for an essential idea in Frencli thought on the ]'>rol)lem of nieta- 

 morphism, since the days of Boue and de Beaumont. 



A formal definition by Studer (1847, page 116) shows how early the 

 conflict began between tlie Lyellian conception of metamorphism and the 

 formally logical use of the word in its literal meaning of "transforma- 

 tion." Translated, Studer's statement runs as follows : "Metamorphism 

 in the broader sense [includes] all effects exercised on rocks through 

 forces other than gravity and cohesion. Metamorphism in the nari'ower 

 sense is confined to rock transformations which are ^oroduced, not through 

 the influence of the atiuosphere or of the water on the earth's surface, 

 but, directly or indirectly, through activities which originate in tlie inte- 

 rior of the earth.-" 



In his Lehrbuch der r4eognosie, C. F. jSTaumann (1850, page 751) dis- 

 tinguished "normal or general metamorphism" from "abnormal or local 

 metamorphism." Translated, his words are : '^'N'ormal metamorphism is 

 the transformation of a rock through a f[uite general cause, which has 

 affected the rock in its ciitire extension and represents a regular (gesetz- 

 massigen) and necessary phase in tlie gradual development of the rock. 

 Abnormal metamor2:>hism is the trajisforniation of a rock through ex- 

 traordinary causes, a transformation which has affected the lock only in 

 certain parts of its exteint, "without marking a necessary stage in the 

 development of the rock." 



Among the phases of normal metamorphism Xaumanu included tbe 

 consolidation (cementation) of sand, pebbles, and mud — to form, respect- 

 ively, sandstone, conglomerate, and argillite. He recognizes, however, 

 that many of the transfornuitions necessary in the development of a rock, 

 such as cementation, aiul also the changes in rocks produced by volcanic 

 exhalations, are not covered l)y "metamorphism in the narrower sense." 

 Xaumann stated that the use of the woid in the narrower sense was cus- 



