Reviews—Die Sulfid-Sulikatschmelzloswngen. 89 
silicates, rather than with the more calcareous diopside-rocks or 
normal gabbros. A few sulphide masses of this type are found along 
with olivine rocks, especially peridotites. The physical chemistry 
and equilibria of the norite magmas are discussed, and it is shown 
that many of them approximate closely to eutectic composition 
-(anchieutectic rocks). Most of the great pyrrhotite deposits are 
associated with norites that contain more hypersthene than corre- 
sponds to the eutectic limit between labradorite and hypersthene ; 
where felspar is in excess sulphide segregations are much less 
common. In the cases described it is quite clear that the pyrrhotite 
crystallized later than the pyroxenes, olivine, and_ felspars. 
Incidentally it is of interest that, however quickly cooled, sulphides 
are always completely crystalline; no such thing as sulphide glass 
is known to exist. This behaviour is in strong contrast to that of the 
silicates. Likewise, it appears that owing to the highly mobile 
nature of fused sulphides, under-cooling does not occur to any 
appreciable extent, but sulphides crystallize sharply close to their 
true freezing- point. 
All the phenomena attending the occurrence and crystallization 
of the sulphide segregations and their consanguineous silicate rocks 
become easily intelligible when it is once fully realized that silicates 
and sulphides possess very limited mutual solubility, and at 
the normal temperature of intrusion must of necessity form two 
liquid phases; this conception greatly helps in the solution of the 
problem of the genesis of the great nickel deposits of Sudbury and 
others, a problem which has of late years led to so much discussion by 
many petrologists, both from its inherent interest and from its great 
technical importance. 
Viva dale Jay, 
