W. N. Benson — Origin of Serpentine. 701 



of the main mass of the rock, so that this process cannot 

 be the result of atmospheric weathering, but of magmatic 

 solutions (Weinschenk 1891, 1894). This important 

 work will be further discussed below. By this hypothe- 

 sis of crystallization under high pressure, a definite form 

 was given to the. vague conception of a hydrous magma, 

 previously suggested by Daubree and the Italian work- 

 ers. Becke, who studied an adjacent mass of antigor- 

 ite-serpentine at the same time, also recognized that 

 pressure was essential to its formation (Becke 1894). 

 Somewhat similar phenomena have been described by 

 Palache (1907), who found a narrow vein of olivine, two 

 inches in width, traversing a serpentinized mass of peri- 

 dotite made up of "platy serpentine" (antigorite?), and 

 chiefly replacing olivine but also pyroxene. The olivine 

 of the vein is vitreous in appearance, is in large crystals 

 associated with chrysotile and sometimes brucite, and is 

 sharply bounded from the massive rock. 



Support was given to the hypothesis of the origin of 

 antigorite under pressure by Bonney (1905, 1908), but 

 though thus demanding the deep-seated origin of antigor- 

 ite, he does not conclude that it must result from the 

 action of magmatic waters. Lindgren (1895) also advo- 

 cated the deep-seated origin of serpentine, and the 

 absence of any atmospheric action, pointing out that no 

 change in the character of the serpentine is to be seen at 

 whatever depth it is encountered in mining operations. 

 Mennell has recently given evidence from South Africa 

 corroborating this (1913). The most striking evidence 

 of this known to the writer has not apparently been cited 

 in discussions on this subject. Five kilometers inward 

 from the north portal of the St. Gotthardt tunnel, and at 

 a depth of 950 meters from the surface, is a mass of ultra- 

 basic rock, 450 meters in width. On either side there is 

 a marginal band of talcose carbonate (magnesite) rock, 

 and within this there is on either side of the mass and 

 again near its center, a zone of completely serpentinized 

 rock,- while between the serpentine zones there is par- 

 tially hydrated peridotite with 5-3% H 2 0. This repetition 

 of the central peridotite is believed to be due to fault- 

 ing. The facts are displayed on fig. 1 (Stapff, 1878, 

 1880, Bodmer-Beder 1903.) Almost directly above this 

 serpentine in the tunnel, there occurs on the surface a 

 mass of peridotite, surrounded by serpentine and car- 



