25

and some of the hornblende and augite are chloritized. It is probable that
some of the baking or induration of the Antler shales is due to the intrusion
of the sills.

Age and Correlation. Since the Antler cherts and shales are the
youngest consolidated rocks in the area, it was impossible to date the
intrusion of the sills. The fracturing and faulting which they have suffered
points to the conclusion that they were intruded before the Slide Mountain
series was folded. They are tentatively correlated with the Coast Range
(Jurassic) period of intrusion.

TERTIARY

Deposits that are fairly definitely known to be Tertiary in age occur only
sparingly in the area and are not exposed except in artificial excavations.
Even in the bottoms of narrow drift-filled valleys such as those of Lowhee
and Mosquito creeks, where the bedrock has been exposed by hydraulick-
ing, glaciated boulders are found in places resting on the bedrock, so that it
is evident that nearly all the gravel filling is glacial in origin. There are,
however, on the sides and near the bottom of Lowhee creek, on Williams
ereek near the mouth of Milk gulch, and at other places in the district,
localized adherences on bedrock of partly cemented gravels which differ
from the glacial gravels in that they contain no glaciated stones and which
are, therefore, almost certainly Tertiary.

There are also in places—for example, in Lowhee valley—numerous
angular blocks of the country rock—“‘slide-rock”’ of the miners—which rest
on the true bedrock in the valley bottom. The slide rock is ancient talus
derived from the rock sides of the valley and, as it underlies the glacial
drift, is probably Tertiary. It forms, however, only a very small part of the
valley filling, and probably occurs only in a few of the narrow valleys
which were not eroded to any great extent by the glaciers of the
Pleistocene period. In the broad valleys—such as “The Meadows”—
which were probably overdeepened by ice-erosion; as is shown on pages 122
& 125, there can, of course, be no Tertiary deposits present. The dumps of
many of the old placer drift mines—for example, on Jack of Clubs creek and
above Stanley on Lightning creek—in many cases show what is descri bed by
the placer miners as ‘flat wash, which formed the bedrock gravels and con-
tained the richest deposits of placer gold. The ‘‘wash” consists of angular
and partly worn fragments of country rock and quartz veins, and in
many cases contains stones of heavy rocks and minerals, such as barytes,
galena, etc. It is partly cemented in places. The stones are nearly all
local in origin and show no evidences of glacial action, so that it is probable
the gravels from which the tailings were derived and which have been largely
mined out were Tertiary. No fossils which would throw light on the age
of the deposits have been found. There were, probably, large quantities of
gravels in the Tertiary valleys of the area, but these were largely reworked
during the Glacial period, so that only small amounts of the Tertiary
deposits remain.

Residual gravels—that is, gravels consisting dominantly of a resistant
rock such as quartz—are only locally present in the area. This is appar-
ently due to rapid stream erosion in late Tertiary time, when, as a result of