694 W. N. Benson — Origin of Serpentine. 



necessary to investigate this matter for the fuller under- 

 standing of the field-work undertaken, there seemed here 

 an opportunity to accept the invitation to enter this field 

 of research. In this the writer had the great privilege of 

 working in Cambridge under the guidance and with the 

 generous help of Professor Bonney. He has also been 

 able to study material from Great Britain, the Pyrenees, 

 Switzerland, Germany, Austria, Australia, and New Zea- 

 land in the collections of Bonney, Becke, Lacroix, Preis- 

 werk, Posenbusch and Weinschenk, of the Geological 

 Survey of Great Britain and of several Continental and 

 Australian universities. The paper discusses chiefly the 

 origin and alteration of the serpentines derived from plu- 

 tonic masses ; it does not deal in detail with the physical 

 characters of the different serpentine minerals, which have 

 been recently exhaustively reviewed by Bonney (1905, 

 1908 ), 1 and Lacroix (1903), or of the chemical features, 

 which have been treated by Leitmeier (1913). For a 

 complete treatment of the whole subject it would have 

 been necessary to review fully the origin of nephrite in 

 serpentine-masses, and of the alterations undergone by 

 olivine in volcanic rocks, but to these points the writer's 

 studies have been less directed, and they are, therefore, 

 but briefly considered. 



II. The Recognition of the Intrusive Character of Serpentine- 

 masses. 



The origin of serpentine has been discussed since the 

 beginning of the scientific study of geology. The earliest 

 work has been summarized at various times by Weigand 

 (1875), Hunt (1883), Teall (1883), "Weinschenk (1891), 

 and Zirkel (1894), so that we may devote our attention to 

 the last two decades. The close association of the ser- 

 pentines with the crystalline schists, and often with the 

 crystalline limestones on the one hand, and with the mas- 

 sive igneous rocks on the other, long proved a source 

 of perplexity. So also did the extreme rarity of dikes of 

 serpentine crossing the structural planes of the rocks in 

 which they occur. Patrin, De Saussure, Humbolt, Bay- 

 reuth, and Jameson considered the serpentine to be 

 regularly interbedded with the stratified series, while 



1 The dates given with the names of authors refer to articles noted in 

 the bibliography at the end of this paper; in this list the full titles have 

 of necessity been omitted in most cases. 



