Program, Abstracts, and Guidebooks - University of Minnesota Duluth

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DESCRIPTION OF STOPS
The town of Marathon is at one of the few naturally protected
harbours along this part of the North shore of Lake Superior.
An extensive sand and gravel deposit underlies the townsite
and extends eastward to Heron Bay and northward approximately 2½
miles. +
the north these sand and gravel deposits are seen to
overlay broad terrace of varved clays which trends parallel to
the present course of the Big Pie River for more than 50 miles
(Farrand, 1960).
There are at least six beach terraces at Marathon (Thomson,
1934; Puskas, 1964). The highest beach is 710 feet above Mean
Sea Level or 108 feet above the present surface of Lake Superior
(Hough, 1958). The vertical interval between these beach terraces
is 5 to 45 feet. Walker (1956) states that the vertical interval
between terraces occurring 20 or more miles to the west is 5 to
10 feet. These differences may indicate a relative increase in
the rate of post glacial isostatic adjustment to the east in dir—
ection of the Marathon area.
qae
0.0 Intersection of Highway 17 and turn off to Marathon.
Continue south east on Highway 17.
2.4 Eastern contact of Massif with country rock.
STOP 1 (Fig. 1 & 2) is a 2 mile traverse across the eastern part
of the massif beginning at the contact of gabbro and
anatexite. (Fig. 2)
Because of the close proximity of, the country rocks
to a considerable portion of the traversed gabbros, the
gabbros are highly charged with xenoliths, variably assimilated,
and variably hybridized.
STOP1A EASTERN CONTACT OF MASSIF (Fig. 2).
The local contact zone between gabbro, occurring as
a topographic 'high', and anatex±tes shows the following
features;
(1) in plan, the contact appears flexured
or arcuate.
(2) dip relations of contact indicate 'on—
lap' by anatexite.