MINERALOGY OF BLACK LAKE AREA. 
75 
solutions producing the metamorphism were charged with CO 2 . These 
two types of serpentinization may be represented by the equations 
(1) 3Mg 2 Si0 4 + SiO* + 4H 2 0 2H 4 Mg 8 Si s 0# 
(2) 2Mg 2 SI0 4 + CO, -f 2H*0 -> IhMgtSijA-f MgCOs. 
If the metamorphism takes place through the agency of siliceous 
waters, serpentine is the only product necessarily formed, with perhaps 
some iron oxide (magnetite) if the olivine of the peridotite is an iron- 
bearing variety; but serpentinization by means of carbonated waters 
necessitates the simultaneous formation of a considerable amount of 
magnesium carbonate. Since the rocks of the area are free from carbon- 
ate, except in very minor amounts, the evidence points to siliceous and 
not carbonated waters as the reagent which has been responsible for 
the serpentinization. 
There yet remains the question as to the source of these waters, 
whether they were of meteoric or magmatic origin ; and here again there 
is no certain proof for either of these alternatives. The field evidence, 
however, points to a connexion between the granite dykes and the amount 
of serpentinization ; and it seems most probable that the metamorphism 
was brought about by magmatic solutions which accompanied the 
injection of these dykes, or which were not required in the composition 
of the dykes and were expelled as the latter consolidated. 
Mode of Origin of the Chrysolite. 
Various theories have been advanced to explain the origin of the 
chrysotile veins, and references to the literature dealing with this subject 
will be found in the reports of Cirkel and Dresser. It will be sufficient 
to reproduce here the conclusions arrived at by the latter author as the 
result of an extended examination of the district - 1 
"The position, size, and number of asbestos veins in rich ground, 
make it inconceivable that the spaces they now occupy were once open 
fissures, and especially that many of them were open at the same time. 
Open fissures up to 2 inches in width, running in all directions from 
vertical to horizontal, extending 100 feet or more in length, and occupying 
in places as much as 10 per cent of the entire rock, would be a mechanical 
impossibility. The possibility remains of crevices having been enlarged 
and filled by replacement. 
“But the asbestos of the veins is practically identical in chemical 
composition with the serpentine of the walls, which is strong evidence 
against the material composing the veins having been brought in either 
from above or below. Segregation from the walls also would imply a 
difference in chemical composition, which does not exist. In other 
1 Op. dt-, p. 65. 
