DEFINITION Ol'^ METAiMORrniSM ■ 379 



tomary in 1850. He specially emphasized tke rise of the isogeotherilis in 

 geos3'nclinals as one important condition for normal metamorphism, bnt 

 makes no mention of monntain-hnilding in this connection. 



According to Naumann, al)normal or local metamorphism is chai'acter- 

 ized by '^evident" canses, in contrast to the more hidden or "latent'^ (von 

 Morlot) canses of normal metamorphism. The chief '^evident" canses he 

 lists : (1 ) coml)nstion, as in the case of changes in clays through the l)urn- 

 ing of a coal Ijed; (2). volcanic gases and vapors^ as in the conversion of 

 limestone into gypsnm by exhaled hydrogen sulphide; (3) magmatic heat 

 at igneous contacts^ and (4) impregnation with water and hydrous solu- 

 tions^ as in the case of local dolomitization or silicification. 



Delesse (1857, page 90) lield tliat "metamorphism in its most general 

 meaning" includes all alterations undergone ])y j-ocks. He made the dis- 

 tinction l)et\veen normal or general metamorphism and abnormal or special 

 metamorphism/ the former being due to invisible causes, the latter being 

 due to "accidental but visible'' causes operating over small, separated 

 areas. This dichotomous division carries the implication that, for prac- 

 tical purposes, Delesse really excluded weathering from the list of meta- 

 morphic processes. 



Daubree (1860, page 59) introduced the expression '^metamorphisme 

 regional'^ as an improvement on ("plus juste que") "metamorphisme 

 normal" and as less vague than "metamorphisme general." He gave no 

 formal definition of regional metamorphism. Though dwelling on the 

 role of crustal deformation in the evolution of the Precaml^rian gneisses 

 and schists, Daubree argued energetically against strict uniformitarianism 

 as applied to the genetic problem of the crystalline schists. He wrote 

 (page 123) : "The old gneisses testify to the high temperature of the 

 earth's surface in ancient times." 



In the present connection Lossen's writings are notewortliy for two 

 reasons. He included lithifaction or consolidation (Festwerdnng) of 

 sediments among the motamorphic processes. He introduced (1875, page 

 970, or at an earlier date) the first technical name, "Dislocationsmetamor- 

 phismus," for the concept already described by Baur, Sharpe, Sorby, and 

 others, and now generally called dynamo-metamorphism or dynamic meta- 

 morphism. 



Yon Hauer (1878, page 109) defined "metamorphism in the widest 

 sense" as including "the sum of tlie changes which rocks undergo after 

 their formation (Bildung), throngh tlie influence of heat, or chemical 

 agents, or of both together, . . . the changes not going so far that the 

 masses are completely desti'oyed (zerstort) and therewith cease to be rocks 

 (Gebirgsarten)." In this sense he held that all rocks are metamorphic; 



