107 



has speculated on the possibility of certain serpentines having been deposited 

 as such from the primordial ocean along with the crystalline schists with 

 which they are often so intimately associated. 



The formation of serpentine in connection with the alteration of felspar 

 has been described by several observers. 1 X) The following chemical reactions 

 established by BISCHOF show the possibility of such an event : 



(1) Silicate of lime is decomposed by magnesium sulphate or chloride ; 



with the formation of magnesium silicate and calcium sulphate 

 or chloride. (2) 



(2) Aluminium silicate is decomposed by magnesium sulphate or 



chloride ; with the formation of magnesium silicate and 

 aluminium sulphate or chloride. (3) 



(3) Calcium silicate and magnesium bicarbonate form magnesium 



silicate and calcium bicarbonate.* 41 



(4) Potassium silicate and magnesium bicarbonate form magnesium 



silicate and potassium carbonate. (5) 



It will be observed that in all these cases the reactions are of u 

 complicated character. The production of serpentine from felspar by the 

 simple action of water charged with carbonic acid and oxygen is an im- 

 possibility, for alumina as well as lime must be removed. Such a production 

 does not appear impossible if we bring to our aid solutions of magnesium 

 chlorides and sulphates. If, however, instead of considering chemical 

 possibilities, we turn to nature and ask if there be any evidence of the 

 development of serpentine on a large scale in connection with the alteration 

 of felspar we appear to meet with a negative answer. The substance 

 analysed by Professor HEDDLK (6) from the gabbro of Beauty Hill, Aberdeen, 

 contains 12'444 p.c. of alumina and is, as indeed he himself points out, a 

 massive variety of pennine (pseudophite) and not a true serpentine. 



So far we have been considering serpentine from a chemical and 

 miiieralogical, rather than from a geological standpoint. We have now to 

 go back in time and describe the important work of SAXDBERGER and 

 TSCHERMAK on the origin of serpentine rock-masses. 



In 1866, SANDBERGER (7) arrived at the conclusion that many .serpentines 

 have been produced by the alteration of oli vine-rocks (peridotites). He 

 observed in the serpentine of several localities nodules of olivine-rock which 

 were not bounded by any hard and fast lines, but which passed gradually 

 into the surrounding mass. Seeing that the formation of serpentine from 

 olivine had been definitely established, he concluded that these transitions 

 in space indicated corresponding transitions in time, and regarded the olivine- 



(1) See HEDDLE. Traiu*. Royal Soc. Edin. 1879. Vol. XXVIII., p. 544. 



(2) BISCHOF. Chemical and Physical Geology. Eng. Edit. Vol. II., pp. 66 and 67. 



(3) Ibid. p. 69. 



(4) Ibid. Vol. I., p. 13. 



(5) Ibid. Vol. II., p. 69. 



(6) Trans. Royal Soc. Edin. 1879. Vol. XXVIII., p. 543. 



(7) N.J., 1866, p. 391. 



