| Symbol |
Geologic Unit |
Materials |
Topography |
Origin |
| a |
Stream alluvium (includes Holocene flood plain,
stream terrace, and alluvial fan deposits) |
Sand, gravel, and silt. |
Flat to gently sloping on flood plains and
stream terraces; gently to moderately sloping on alluvial fans. |
Deposited on flood plains and stream beds by
postglacial streams. |
| s |
Swamp, marsh, and bog deposits (includes both
fresh-water and salt-water marshes) |
Peat, muck, clay, silt, and sand. |
Flat. |
Formed by accumulation of sediments and organic
material in depressions and other poorly drained areas. |
| b |
Beach deposits |
Sand and gravel. |
Gently to moderately sloping, with low ridges
and mounds. |
Includes beach sediments formed by wave and
current action, and sand dunes derived from these deposits. |
| eb |
Emerged beach deposits |
Sand and gravel. |
Low ridges or sloping surfaces. May be
associated with wave-cut benches on hillsides. |
Formed by wave erosion of till or other
materials during the late-glacial marine submergence of parts of
southern Maine. |
| e |
Eolian deposits |
Sand. |
Dune ridges and mounds, or blanket deposit that
conforms to surface of underlying unit. |
Windblown sand. Derived from wind erosion of
glacial sediments and deposited in late-glacial to postglacial time. |
| L |
Lake-bottom deposits |
Silt, clay, and sand. Commonly well stratified,
and may be rhythmically bedded. |
Flat to gently sloping except where dissected by
modern streams. |
Composed of sediments that washed out of late
Wisconsinan glacial ice and accumulated on the floors of glacial lakes.
Map unit may also include a few non-glacial lake deposits. |
| m |
Glaciomarine deposits (fine-grained facies) |
Silt, clay, sand, and minor amounts of gravel.
Commonly a clayey silt (the Presumpscot Formation). Sand is dominant in
some places, but may be underlain by finer grained sediments. Locally
fossiliferous. Map unit includes small areas of till and other units
that are not completely covered by marine sediments. |
Flat to gently sloping except where dissected by
modern streams. Commonly has a branching network of steep-walled stream
gullies. |
Composed of glacial sediments that accumulated
on the ocean floor. Formed during the late-glacial marine submergence
of lowland areas in southern Maine. |
| ms |
Glaciomarine deposits (coarse-grained facies) |
Sand, gravel, and minor amounts of silt. |
Flat to moderately sloping. Steeper on
ice-contact slopes and delta fronts. May be kettled where deposited
over stagnant ice blocks. |
Deposited where glacial meltwater streams and
currents entered the sea. Includes glaciomarine deltas, subaqueous
kames and fans (subaqueous outwash), and outwash that prograded into
shallow marine waters and locally covered earlier glaciomarine silt and
clay deposits. |
| go |
Glacial outwash deposits |
Sand and gravel. |
Flat to gently sloping. Steeper on ice-contact
slopes and delta fronts. May be kettled where deposited over stagnant
ice blocks. |
Deposited by meltwater streams in front of the
receding late Wisconsinan ice margin. Includes non-marine outwash
plains, deltas, and fans. |
| g |
Ice-contact glaciofluvial deposits (exclusive of
eskers) |
Sand, gravel, and silt. |
Flat-topped kame terraces and deltas which are
locally kettled and bounded by steep sides, or hummocky terrain with
numerous kames and kettles. |
Deposited by meltwater streams adjacent to
stagnant glacial ice. |
| ge |
Eskers |
Gravel and sand. May include minor amounts of
till. Portions of many eskers below the marine limit are partly or
entirely buried by glaciomarine deposits. |
Individual or multiple ridges. Complex eskers
may have anastomosing patterns and be gradational with other types of
ice-contact deposits. |
Chiefly deposited by meltwater streams flowing
in tunnels within or beneath the late Wisconsinan ice sheet. Map unit
also includes small undifferentiated areas of units "g" and "go". |
| sm |
Stagnation moraine |
Mostly till, but also includes variable
percentages of undifferentiated sand and gravel. |
Undulating topography with local hummocks and
ridges. |
Deposited during the dissipation of stagnant
glacial ice. |
| em |
End moraines |
Till or sand and gravel. May be very bouldery.
Commonly interbedded with or overlain by glaciomarine sediments in
areas that experienced late-glacial marine submergence. Only the
largest end moraines and some dense clusters of smaller ones are shown
here as a separate unit (em). Elsewhere, short lines mark the crests
of moraine ridges, which are locally so numerous that only selected
individuals are represented. |
Ridges. Commonly arcuate, discontinuous, and in
groups. May be multi-crested and hummocky. Size range: 1-30 m high,
5-200 m wide, and 30 m to over 10 km long. |
Deposited in the marginal zone of the late
Wisconsinan ice sheet, by glacial ice and/or meltwater flowing out of
the ice. |
| rm |
Ribbed moraine |
Till is the principal constituent, but
stratified sediments are present in some of the deposits. |
Numerous hummocks and short sub-parallel ridges
which typically occur in lake basins and other lowland areas. |
Origin uncertain. Deposited either at the margin
of or beneath the late Wisconsinan ice sheet. |
| t |
Till |
Heterogeneous mixture of sand, silt, clay, and
stones. May include many boulders. Generally massive, but in many
places contains beds and lenses of variably washed and stratified
sediments. |
Generally a blanket deposit that conforms to the
underlying bedrock topography. Also forms drumlins and other glacially
streamlined hills. |
Deposited directly by glacial ice. |
| |
Thin drift |
Area of many bedrock outcrops and/or thin
surficial deposits (generally less than 3 m thick). The type of
surficial material is known or inferred. |
Topography of these areas reflects the
configuration of the bedrock surface and ranges from smooth undulating
hills to knobby terrain and high mountains. |
Commonly the result of non-deposition of glacial
sediments, but the surficial materials in some coastal areas have been
largely removed by marine erosion in late-glacial time. |
| |
Thin drift, undifferentiated |
Area of many bedrock outcrops and/or
near-surface bedrock where the surficial materials have not been mapped. |
Same as other thin-drift areas. |
Same as other thin-drift areas. |
| rk |
Bedrock |
Area of extensive bedrock outcrop, or where the
bedrock has only a thin cover of soil and vegetation. Surficial
deposits are essentially absent. Particularly common on the ridge
crests and steeper slopes of mountainous areas. |
Hilly to mountainous terrain. |
Same as the thin-drift areas. |
| Contact |
Boundary between adjacent map units. |
| Moraine ridge |
Lines mark the crests of individual end
moraines. Symbol also is used in conjunction with unit rm to show
orientation of drift ridges of uncertain origin. |
| Glacial striation locality |
Includes striations, grooves, crag-and-tails,
and other types of ice-flow indicators on bedrock outcrops. Dot
indicates point of observation. Arrowhead is omitted where ice-flow
direction is uncertain. Flags indicate older trends. |
| Glacially streamlined landform |
Symbol shows long-axis orientation of drumlins,
fluted till ridges, roches moutonnees, and other hills that have been
elongated parallel to the flow of glacial ice. |
| Cirque |
Steep-walled, semicircular bedrock basin formed
by glacial erosion in high mountainous areas. |
| Meltwater channel |
Channel eroded by glacial meltwater stream.
Arrow indicates known or inferred direction of stream flow. |
| Glaciomarine delta |
Number indicates surveyed altitude (in feet) of
contact between topset and foreset beds, or of meltwater channel on
delta surface, which approximately marks position of sea level in
late-glacial time. |
| Glaciolacustrine delta |
Number indicates approximate altitude (in feet)
of former glacial-lake surface. |
| Delta of uncertain origin |
Delta formed near limit of late-glacial marine
submergence. Number indicates approximate altitude (in feet) of contact
between topset and foreset beds. |
This list includes locations of important stratigraphic sections of
Pleistocene deposits in Maine, and places where good examples of
certain glacial features can be seen. The sites were selected partly on
the basis of accessibility, ease of observation, and relative
permanence. Some features, such as eskers and DeGeer moraines, are so
numerous that only a few of the best examples are included here.
Material that predates or is
contemporaneous with the advance of the late Wisconsinan ice sheet.
Material that predates or is
contemporaneous with the recession of the late Wisconsinan ice sheet.
Material that approximately dates the
onlap of the sea during the late-glacial marine transgression.
