Purgatory Quadrangle, Maine
Bedrock geologic mapping by
David P West, Jr. and Evan D. Ellenberger
Digital cartography by Geologic editor Cartographic design and editing by
Susan S. Tolman Henry N. Berr y IV Robert D. Tucker
Robert G. Marvinney
Funding for the preparation of this map was provided in part by the U.S. Geological Survey
STATEMAP Program, Cooperative Agreement Nos. 06HQAG0026 and 07HQAG0079.
Maine Geological Survey Open-File No. 08-35
Address: 22 State House Station, Augusta, Maine 04333
Telephone: 207-287-2801 E-mail: firstname.lastname@example.org This map supersedes
MAINE Home page: http://www.maine.gov/doc/nrimc/nrimc.htm Open-File Map 07-56.
EXAMPLES OF BEDROCK TYPES AND NOTABLE FEATURES
Note: These photographs are included for illustration only. Public access on the Maine Turnpike is dangerous and prohibited. Special permission
to the locations is not implied. Any locations on private property require from the State Police was obtained by the geologist for access to the
permission of the landowner before being visited. In particular, stopping Turnpike localities shown here.
Photo 1. Migmatitic gneiss of the Nehumkeag Pond Formation (Onp), Photo 2. Layered granofels of the Hutchins Corner Formation(?)
partly covered by lichen. The darker gray layers contain more black mica (SOhc?). Its smooth surface is a reflection of the granular texture of the
(biotite) than the lighter gray layers. The foliation is defined by the layers. rock, a characteristic of granofels. The hammer rests on a thick layer of
There is a prominent area of granite in the lower right corner of the slightly rusty weathering quartz-plagioclase-biotite granofels. The
photograph. Thinner layers and wisps of granitic rock are scattered lighter, greenish-gray layer to the left of the hammer point consists of
through the gneiss. The presence of granite in the gneiss makes it a calc-silicate granofels. Granofels of these two compositions is
migmatite. Road cut on Maine Turnpike north of Pleasant Pond, east interlayered in the Hutchins Corner Formation. West side of Stevenstown
edge of map. Road, about 4000 feet north of Lunts Hill Road, Litchfield.
Photo 3. Medium gray, medium-grained thinly layered granofels of the Photo 4. S illimanite-garnet schist of the Waterville Formation (Sw).
Waterville Formation (Sw). D arker layers have a higher content of black Elongate, milky white grains are sillimanite. Garnets are tiny, round,
mica (biotite). East of Jimmy Pond, Litchfield, near west edge of map. pinkish grains. The alignment of minerals from left to right in this
photograph defines the foliation, or schistosity, an important aspect of the
rock structure. Same location as Photo 3.
Photo 5. Characteristic ribbed weathering pattern of impure marbles of Photo 6. Light bluish gray impure marble with discontinuous layers of
the Waterville Formation (Swm). The raised ribs are rich in more dark gray biotite granofels. Waterville Formation, calc-silicate granofels
resistant silicate minerals such as diopside and quartz, while the recessed and impure marble member (Swc). East of Sand Pond, about 3000 feet
layers are dominated by more easily weathered calcite. Northern end of south of Route 9 and 126.
Sheep Island in the southern part of Cobbosseecontee Lake.
Photo 7. Coarse-grained sillimanite schist of the Waterville Formation Photo 8. D eeply rusty weathering schist and granofels. Waterville
(Sw). Large white to bluish-white masses are sillimanite. Silvery Formation, rusty schist and granofels member (Swr1). On slope west of
reflective flecks are white mica (muscovite). South side of Route 9 and Sand Pond, about 4000 feet east of South Monmouth.
126, near Hatchery Road intersection, Monmouth.
Photo 9. Light purplish-gray biotite granofels interlayered with pale Photo 10. Litchfieldite, a cancrinite-bearing, biotite nepheline syenite of
greenish calc-silicate granofels of the Vassalboro Formation (Sv). South the Litchfield pluton (PDls). The cancrinite (C) is yellow, biotite (B) is
side of Route 9 and 126, west of Whippoorwill Road intersection, north black, nepheline (N) is gray, alkali feldspar (A) is a cream color, and
end of Oak Hill, Monmouth. sodalite (S) is pale blue. Nepheline, cancrinite, and sodalite are all miner-
als characteristic of alkali-rich intrusive rocks. Approx. 3500 feet north of
Dennis Hill, Litchfield (Locality 23 of Thompson and others, 1998).
JUSTIFICATION FOR THE MAPPED FAULTS REFERENCES
Messalonskee Lake thrust fault. The contact between the Waterville Barker, D.S., 1965, Alkalic rocks at Litchfield, Maine: Journal of
and Sangerville Formations is mapped as a continuation of the Petrology, vol. 6, no. 1, p. 1-27.
Messalonskee Lake thrust, postulated in the Waterville area by Osberg Bayley, W. S., 1892, Eleolite-syenite of Litchfield, Maine, and Hawes'
(1988). Os berg (1988, p. 68-69) interprets the fault to be east-dipping and hornblende syenite from Red Hill, New Hampshire: Bulletin of the
to have formed prior to regional metamorphism and prior to the dominant Geological Society of America, vol. 3, p. 231-252.
phase of upright folding. This fault is shown by Tucker and others (2001) Hussey, A. M., II, 1983, Bedrock geology of the Lewiston 15' quadrangle,
to the northeast, and by Hussey (1983) and Moench and others (1995) to Maine: Maine Geological Survey, Open-File 83-4, map scale
the southwest of the Purgatory quadrangle. 1:62,500.
Marvinney, R. G., in preparation, Bedrock geology of the Augusta 7.5'
Unnamed thrust fault. A thrust fault through the middle of the quadrangle, Maine: Maine Geological Survey Open-File map, scale
quadrangle is proposed here to account for lithologic differences across it. 1:24,000.
The central issue is whether the broad unit of granofels east of the fault Moench, R. H., Boone, G. M., Bothner, W. A., Boudette, E. L., Hatch, N.
(SOhc?) belongs to the Vassalboro Formation or the Hutchins Corner L., Jr., Hussey, A. M., II, Marvinney, R. G., and Aleinikoff, J. N., 1995,
Formation. Osberg (1988) defined the Hutchins Corner Formation as Geologic map of the Sherbrooke-Lewiston area, Maine, New
those granofels rocks stratigraphically below the Waterville Formation, Hampshire, and Vermont, United States, and Quebec, Canada: U. S.
and Osberg (in Tucker and others, 2001) re-established the use of the Geological Survey, I-1898-D, 56 p., map scale 1:250,000.
Vassalboro Formation for granofels above the Waterville. Unfortunately, Osberg, P. H., Boone, G. M., and Hussey, A. M., II, 1985, Bedrock
reliable stratigraphic facing indicators at formational boundaries are geologic map of Maine: Maine Geological Survey, scale 1:500,000.
lacking in the Purgatory quadrangle, so the tentative assignment here of Osberg, P. H., 1988, Geologic relations within the shale-wacke sequence
rocks to the Hutchins Corner, which presumes they are older than the in south-central Maine, in Tucker, R. D., and Marvinney, R. G.
Waterville, is based on the following, less compelling observations from (editors), Studies in Maine geology, Volume 1: structure and
this quadrangle. Granofels of the Vassalboro is generally a lighter color stratigraphy: Maine Geological Survey, p. 51-73.
than that of the Hutchins Corner, presumably due to a lower proportion of Thompson, W. B., Joyner, D. L., Woodman, R. G., and King, V. T., 1998,A
biotite. Granofels of the Vassalboro is typically not rusty weathering, collector's guide to Maine mineral localities, Maine Geological
while that of the Hutchins Corner is slightly to moderately rusty Survey, Bulletin 41, 133 p.
weathering on foliation surfaces. Calc-silicate rock and mica schist layers .
Tucker, R. D., Osberg, P H., and Berry, H. N., IV, 2001, The geology of a
are generally more abundant in the Vassalboro than in the Hutchins part of Acadia and the nature of the Acadian orogeny across central
Corner, although mica schist is not common in either formation. Finally, and eastern Maine: American Journal of Science, v. 301, p. 205-260.
bedding is generally slightly thicker in the Vassalboro than in the Hutchins
Corner. A second issue supporting the existence of the proposed fault is
GEOLOGIC TIME SCALE
that there are lithologic differences between the Waterville Formation
(Sw) northwest of the fault and the Waterville Formation (Swgp) to the Geologic Age Absolute Age*
southeast. The granofels and pelite member (Swgp) contains a greater Cenozoic Era 0-65
proportion of granofels, contains much less sillimanite, and includes more
calc-silicate layers (although still not abundant) than the Waterville (Sw) Mesozoic Era 65-253
to the northwest. A third issue is the apparent absence of rusty-weathering Paleozoic Era Permian Period 253-300
schist along the contact between the Hutchins Corner and the Waterville. Carboniferous Period 300-360
This contrasts with the common presence of a prominent unit of rusty- Devonian Period 360-418
weathering rocks along the contact between the Waterville and Vassalboro Silurian Period 418-443
Formations elsewhere (Tucker and others, 2001; Marvinney, in Ordovician Period 443-489
preparation) and northwest of the proposed fault in this quadrangle Cambrian Period 489-544
(Swr1). It is for these three reasons that a fault is proposed here. As with
Precambrian time Older than 544
the Messalonskee Lake thrust, this fault is interpreted to have formed prior
to regional metamorphism and prior to the dominant phase of upright * In millions of years before present. (Okulitch, A. V., 2002,
folding. Échelle des temps géologiques, 2002: Commission géologique du
Canada, Dossier Public 3040 (Série nationale des sciences de la
Terre,Atlas géologique) - RÉVISION.)