W. N. Benson — Origin of Serpentine. 711 



solutions of silica and carbonic acid upon ultrabasic 

 rocks is of world-wide distribution. 



ii. Clarke (1916) declares "that hydrous magnesian 

 silicates are easily prepared by various wet reactions, but 

 these syntheses have little or no significance in the inter- 

 pretation of serpentine. ' ' Nevertheless, Miiller (1877) 

 by acting upon olivine with carbonated waters, found 

 that silica and magnesia were extracted therefrom in the 

 right proportions to make serpentine. He also stated 

 that serpentine was soluble in similar waters even at 

 ordinary temperatures. Leitmeier (1913) has confirmed 

 this, showing that 3-7% of finely powdered serpentine 

 was dissolved in six months by weakly carbonated waters 

 at 15°-18°C, and that magnesian carbonate and gelatinous 

 silica were deposited. This, he says, explains the forma- 

 tion of opal which is frequently associated with car- 

 bonated serpentines. What seems to be most desirable 

 is that a series of experiments should be made upon 

 the action of carbonated waters upon magnesian sili- 

 cates at such pressures and temperatures that might 

 more closely simulate the conditions under which mag- 

 matic waters would act. We shall note below that other 

 dissolved substances than carbonic acid may be instru- 

 mental in serpentinization. 



iii. The development of magnesian carbonate rocks 

 with talc, silica, etc., was studied by Schrauf (1882) on 

 material from Bohemia. He concluded that the change 

 was a continuation of the process of serpentinization, 

 which he referred to the action of epigene waters 

 enriched in carbonic acid by passage through the humus. 

 The serpentinization of the peridotites was followed by 

 carbonation, with the production of chalcedony or opal; 

 and finally by the leaching out of the carbonates, leaving 

 a siliceous skeleton. Such were the final stages of the 

 weathering of the peridotites described by Pratt and 

 Lewis (1905), who, however, recognized that serpentin- 

 ization is not an essential preliminary to such atmos- 

 pheric carbonation. Weinschenk (1894,1913) referred 

 the formation of breunnerite, associated with lime and 

 magnesian silicates in the Tyrol, to an extension of the 

 process of serpentinization, but considered this to be due 

 to the action of post- volcanic waters. Schneider (1912) 

 has adopted a third view, an extension of that of Schrauf, 

 namely that both processes are to be referred to "secu- 

 lar weathering, ' ' as defined by Cornu (1910), which, so 



