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them. This is the more apparent when we recall the small
degree of alteration undergone by the very much older Yakoun
basalts.

The evidence bearing upon the question, what these pro-
cesses probably were, may be summed up here.

The noticeable amount of superheat in many of the intrusives
at the time of their injection is proved by the strong baking
action they have had on the enclosing sediments, as well as by
the very fact of the occurrence of thinly tabular bodies in a
highly liquid condition (Figures 7, 8, and 9) so far from their
sources.

The finely divided pyrite, found as impregnations—that is
replacements—in the dykes and sills and in the adjoining rocks,
for instance, the pyritic nodules near the intrusives, is evidence
of the presence of hot pyritic solutions.

Finally, the great development of chlorite is to be considered.
While chlorite can doubtless be formed under rather low temper-
ature conditions, its frequent occurrence in high temperature
ore deposits! and in chloritic schists shows that its formation
readily takes place under rather high temperature conditions.

The great degree of alteration of the feldspars in the Ethel-
ine intrusives, compared with the less degree of alteration of
the same mineral in the much older Yakoun volcanics indicates
also that the Etheline rocks are exceptionally affected.

With the above facts in mind, the decomposition of the
rocks of the Etheline formation is best explained by supposing
them to have been acted upon by large amounts of heated
magmatic water which may well have been wholly or in part
in gaseous form.

MASSET FORMATION.

The Masset formation is wholly basaltic except for a single
occurrence of a trachyte of bostonitic habit, an unusual rock
type. Wherever examined, with this single exception, basalts
of all varieties of texture, both primary and pyroclastic, were

1 Lindgren, W., ““Mineral deposits,’’ McGraw-Hill Book Co., New York, N.Y., 1913, pp.
617, 627, etc.
Spurr and Garrey, Econ. Geol. vol. 3, 1908, pp. 688-725.
McConnell, R. G., “The Whitehorse copper belt, Yukon Territory,’’ Geol. Surv., Can.,
1909, pp. 21, 22, 23. (In this case the clinochlore is clearly a primary mineral.)

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