T4 
MUSEUM BULLETIN NO. 27. 
The central part of the massive serpentine bands is usually occupied 
by the fibrous variety, chrysotile; this also is dyke-like in shape, i.e. t 
its boundaries against the massive serpentine are roughly parallel to 
one another, and are rather sharply defined. 
There appears to be a fairly constant relation between the total 
width of any massive serpentine band and that of the chrysotile vein 
which it encloses. Attention was first called to this feature by Dresser, 
who, from a number (49) of measurements, found that the entire serpen- 
tine band is about 6 • 6 times as wide as the asbestos vein within it. 
The chrysotile fibres are all arranged parallel to one another, and 
lie in directions normal to the walls of the vein. Usually the fibres are not 
continuous right across the vein, especially in the wider ones, but there 
is a parting, or sometimes more than one, at or near the middle, which 
is occupied by a film of granular iron ore, usually magnetite. 
Carbonates of lime and magnesia occur only in very small amount 
in the serpentine and associated rocks of the area, either in the form of 
veins or otherwise. 
Lastly, granite is frequently found in the vicinity of good asbestos 
deposits, or, stated in another way, an accumulation of asbestos veins 
(and, therefore, also of serpentine bands) can very frequently be noticed 
in approaching the granite dykes. 
Mode of Origin of the Massive Serpentine. 
As has already been stated, the principal rock of the serpentine belt 
in the Black Lake area is peridotite, or a rock intermediate between this 
and pyroxenite, and it is generally agreed that the massive serpentine 
has resulted from the metamorphism of this rock; it is further believed 
that the serpentinization commenced along joints and other cracks, from 
which it proceeded outward in opposite directions. Field evidence 
points to the joints being more or less contemporaneous with the granite 
dykes; in other words, the rocks were shattered during the last phases 
of igneous activity, joint systems were developed, and along some of the 
fissures so formed, the granitic magma was injected. This correlates 
the commencement of the change from peridotite to serpentine with the 
period of granitic intrusion, or some time subsequent thereto. 
While the actual source of the serpentine is thus well established, 
there may still remain some doubt as to the mode by which the change 
has been brought about. The production of serpentine from olivine 
involves, in general, either an addition of S 1 O 2 or a removal of MgO, 
in addition, of course, to hydration. If the reaction was of the first type, 
siliceous waters would supply the necessary reagent; in the second type, 
the excess of MgO must enter into some new form of combination, such 
as carbonate, in which case it would be necessary to asume that the 
