The “Crash Bridge” locality in
Lincoln, Vermont is located along the
New Haven River at the second
bridge east of the Lincoln General
Store. “Crash Bridge” highlights the
geologic unconfomity between Middle
Proterozoic (~1.5 billion years old)
granitic gneiss and amphibolite of the
Eastern Lincoln Massif (basement
rocks) and the overlying basal
conglomerate portion of the Early
Cambrian (~540 million years old)
Pinnacle Formation (cover rocks)
(Stanley et al, 1987 and 1999). The
contact at this location is a thrust fault
marked by sheared biotite schist and
muscovite
schist
with
gneiss
fragments, (Figure 1: Stanley et al,
1987 after Tauvers, 1982).
The Pinnacle basal conglomerate at
“Crash Bridge” is overturned to the
east, tightly folded, and overprinted
by a Paleozoic schistosity of Taconian
age (~410 million years old based on
K/Ar biotite dates from Cady, 1969).
Here the basal conglomerate contains
mostly granitic gneiss cobbles and
boulders that are clast-supported and
arranged in lensoid bodies which
suggest paleochannels. A magnetitebearing quartz muscovite metawacke
matrix separates the clasts. The clasts
in this deposit were shed from
Grenvillian continental rocks into rift
basins that predated the opening of
the Iapetus Ocean.
This site is informally
“Crash Bridge” because
crashed here during a
field trip led by Stanley
_____.
called
a car
UVM
in 19
Take Route 116 south out of Burlington and
follow signs to Lincoln.
References:
Cady, ?, 1969. ???
Stanley, R.S., V. DelloRusso, S.O. O’Loughlin, and E.
Lapp, 1987. The Lincoln massif and its immediate
cover; in Westerman, D., ed., NEIGC 79th Annual
Mtg. Guidebook—1987, Vol. 2, p. 296-313.
Stanley, R.S., T. Rushmer, C. Holyoke, and A. Lini,
1999. Faults and fluids in the Vermont foreland and
hinterland in Western Vermont; in Wright, S.F., ed.,
NEIGC 91st Annual Mtg. Guidebook—1999, p. 135158.
Tauvers, P., 1982. Basement-cover relationships in the
Lincoln area, Vermont, UVM Master’s Thesis, 177p.
For information about other geological teaching
outcrops in Vermont, please contact the
Perkins Geology Museum
Perkins Hall
University of Vermont
Burlington, VT 05405-0122
(802) 656-8694
“CRASH
BRIDGE”
Rolfe Seaton Stanley
Teaching Outcrop
UVM Geology Professor, 1964-2000
Lincoln, Vermont
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