28 THE ROYAL SOCIETY OF CANADA

of feet in length and generally less than 300 feet in width. Some of
them consist only of schistose serpentine, others of massive ellipsoidal
fragments up to 3 feet in diameter in a sheared matrix. Thin sections
were cut from ellipsoids of various sizes, as well as from the sheared
matrix and the schist of the non-fragmental types. In the largest
and least altered ellipsoids, serpentinization has not gone beyond the
chrysotile and mesh antigorite stages. In others, more altered, it
has reached the bladelike antigorite and amorphous serpentine stages.
In all the smaller fragments examined, the serpentinization has
reached the amorphous serpentine stage. The sheared matrix between
the fragments, on the other hand, is always composed of bladelike
antigorite, as is the schist of the non-fragmental shear zones. In the
light of the above observations, it would seem that if shearing and
serpentinization were synchronous, only bladed antigorite forms, and
the same is true if shearing occurred after serpentinization; whereas
under normal conditions of serpentinization, chrysotile, amorphous
serpentine, meshlike and bladelike antigorite may be formed. Du
Rietz (1935, p. 254) in his study of the serpentines of northern Sweden
has come to practically the same conclusion.

A satisfactory theory of serpentinization of the ultrabasic rocks
of the Fort Fraser map-area must explain the following facts: (1) The
serpentinization is confined to the ultrabasic rocks. (2) The serpentini-
zation of the ultrabasic bodies has a haphazard arrangement unrelated
to their borders. It is as intense at the centres of the masses as at
the borders. (3) The areal distribution of the zones of intensity of
serpentinization is in no way related to the proximity of younger
acid intrusives. If the solutions producing serpentinization came
from the younger acid intrusives, hydration would be expected to
increase towards the contacts but this is not the case. (4) Serpentini-
zation is neither confined nor related to fracture zones although, as
indicated in a previous section, antigoritization seems to be favoured
by shearing.

The serpentinization of peridotite has for many years been a
subject of controversy, and those who have studied this problem
favour either one or the other of two theories: (1) That serpentini-
zation 1s brought about by hydrothermal solutions emanating from
later intrusive rocks. Dresser (1913), Graham (1917), and Du Rietz
(1935) advocate this cause. (2) That the serpentinizing solutions
emanated from the cooling magma itself, a theory strongly supported
in recent years by Benson (1918), Phillips (1927), Cooke (1932, 1937),
Haapala (1936), Hess (1983), and other workers.

In the Fort Fraser map-area serpentinization is not related to