W. N. Benson — Origin of Serpentine. 715 



In some regions there is evidence that the peridotitic 

 intrusions were accompanied or followed by the emission 

 of volatile substances such as are usually associated with 

 granitic masses. Thus Bell (1907) found tourmaline in 

 the serpentinous schist in the Parapara District, N. Z. ; 

 Duparc and Siggs (1913) found it in the serpentine of the 

 Urals, and Lacroix (1894, 1901, 1914) found it in associa- 

 tion with scapolite in calcareous rocks invaded by the 

 peridotite of the Pyrenees. His first memoir (1894) 

 describes and discusses a large amount of evidence of 

 this action. 



Occasionally there is also evidence of the expulsion of 

 sodic solutions from the peridotitic magmas, which is 

 perhaps connected with the development of albitic veins 

 in these rocks, to the widespread occurrence of which, the 

 writer has already drawn attention (Benson 1913). 

 Thus Park (1908), citing analyses by Maclaurin, shows 

 that of two otherwise closely analogous mica schists, the 

 one adjacent to the margin of a mass of serpentine at 

 Cromwell, N. Z., contained 8-07% Na 2 as compared with 

 but 2-91% in that two yards from the contact. The well- 

 known glaucophane-schists near the serpentine masses of 

 California first described by Ransome (1893) are some- 

 times cited as an example of this, though doubt has been 

 thrown on their development as a result of contact met- 

 amorphism (e. g. by Nutter and Barber 1902). The 

 occurrence of scapolite in the neighborhood of the Lac 

 du Lherz, as mentioned by Lacroix, recently redescribed 

 by Longchambon ( 1910-1911 ), 3 may be a further example 

 of the emission of soda. Thus we see that associated with 

 the peridotitic intrusions, there are magmatic waters 

 that are charged with carbonic acid and silica, and 

 sometimes with hydrogen sulphide, boric acid, hydro- 

 chloric acid, and soda. Nevertheless the metamorphic 

 action of these magmas is, as is well known, much less 

 marked than that of the more acid rocks. 



3 This paper is interesting as an instance of the application of the 

 special views of a school of French petrologists in regard to the relation 

 of metamorphism, melting down, and mixture of sediments and the fea- 

 tures of "the chemistry of the geosyncline" to the origin of ultrabasic 

 rocks. Lherzolite according to this discussion is produced in a manner 

 following "the general equation granitic magna plus dolomite = C0 2 plus 

 basic magnesian silicates plus pegmatitic f umaroles. ' ' The last term 

 includes inter alia the emission of sodic solutions from the basic magmas. 

 A rather different hypothesis is expounded by Termier (1903). 



