274 GEOLOGY OF THE EITEEKA DISTRICT. 



of every possible Jiiode of occurrence. He followed Buusen in accepting 

 the theory of both an acid and basic magma, but regarding them as 

 parts of the same body of lava. In an appendix to his papei-' he 

 admits the possibility in certain cases of a mingling of lioth types, but 

 objects to the hypothesis of Bunsen as altogether too broad a general- 

 ization. That part of Durochei''s hypothesis which possesses the most 

 originality and upon which he places the most sti-ess to account for the 

 differences in the mineralogical character of lavas has been designated the 

 liquation process applied to igneous rocks. His conclusions, based largely 

 upon chemical analyses, were not substantiated by any array of facts or 

 observations from any one center of A'olcanic energy. Durocher was dis- 

 posed to regard certain lavas as differentiated products obtained by the 

 breaking up of a magma by processes comparable to the separation and 

 segregation of metals in a bath containing several metallic substances in a 

 state of fusion, the theorv being based upon well recognized processes em- 

 jiloyed in metallurgical establishments for the concentration of gold and 

 silver in molten lead. The views enunciated by Durocher have met with 

 slight recognition, but, although containing much that with the advance- 

 ment of knowledge has been shown to be based upon error, they are, in 

 the opinion of the writer, full of the most valuable sugg-estions bearing on 

 the origin of lavas, and entitled to far more consideration than has generally 

 been accorded them. 



Roth's Views.— In 18(il Justus Rotli^ published his hypothesis of " Spal- 

 tung und Dittei-enzirung," in which he elaborated similar views, although by 

 no means identical with those held by Durocher. For the purposes of this 

 chapter it is sufficient to say that the two authors are in accord so far as 

 believing in the power of a magma to split up during crystallization into 

 secondary magmas of different, mineralogical composition. Roth regarded 

 large liodies of crystalline rocks as "Spaltungsproducte," the result of the 

 separating out of certain groups or association of minerals from and de- 

 pendent upon the composition of a primary liquid lava, but governed by 

 varying . conditions of pressure and temperature. His views are derived 



' Op. cit., p. 677. 



- Tabellaiisclie Uebersicht iler Gesteius Aualysen iiud mit kritisclien Erlauterungeu. Berlin, 1861. 



