608 Proceedings of the Royal Society 
Kow the removal of the carbonate of lime from silicate of mag- 
nesia admits of easy explanation, on the supposition that the 
action whereby dolomite limestone is converted into serpentine is, 
as Mr. James Geikie long ago suggested (Quart. Jour. Geol. Sue ., 
1866, p. 533), a hydrothermal action. 
Many theories have been advanced to account for the formation 
of serpentine. Petrologists are nearly all agreed in attributing to it 
in all cases a metamorphic origin. There is, however, some diversity 
of opinion, as to whether it has in every instance been derived from 
volcanic rocks by the alteration of magnesian minerals, or whether 
in certain cases it ought not rather to be regarded as a product 
of the metamorphism of sedimentary rocks. Of its origin in many 
cases from volcanic rocks rich in magnesia there cannot be the 
slightest doubt. 
So long ago as 1835, Quenstedt (Pogg., Ann. 1835, xxxvi 370) 
showed that the celebrated serpentine crystals of Snarum, in South 
Norway, were in reality pseudomorphs of serpentine after olivine, 
and though his views were not universally accepted at the time, 
they have since been fully confirmed both by mineralogists and by 
chemists. Gustav Rose (Pogg., Ann. 1851, lxxxii. 511) showed, 
from the chemical point of view, that olivine would by a slight 
alteration in its composition pass readily into serpentine ; and since 
his time numerous microscopists have demonstrated that the olivine 
of many basalts is in process of undergoing this change. The 
theory of the alteration of volcanic rocks rich in magnesian minerals 
into serpentine, affords a satisfactory explanation of its occurrence in 
veins and dykes. But, on the other hand, its frequent occurrence in 
beds interstratified with limestone, dolomite, and occasionally schists, 
would seem to indicate in these cases a different origin. Rose, in 
the paper already cited, expresses the opinion with regard to 
serpentine in dolomite, occurring in crystalline schistose rocks in 
Silesia, that it has been formed by the alteration of the dolomite. 
Sterry Hunt attributes a similar origin to the serpentines of the 
Laurentian series in Canada (Phil. Mag., 1857, xiv. 388). Yolger 
(Entwickelungsgeschichte dev Mineralien der Talc-glimmer Familie ) 
adopts the same view, and more recently Mr. James Geikie has 
applied this theory to explain the formation of the serpentine of 
Garrick in Ayrshire (loc. cit.). 
