The Glacial Features (Line) layer describes linear features associated with surficial
geology. These glacial features include, but are not limited to, Wisconsinan
synglacial sea extents, meltwater channels, meltwater spillways, ice margins and eskers.
This layer also includes non-glacial exposures such as gravel pit extents. An associated
DBASE table (GLAC_DESC166L.dbf) is available with glacial feature descriptions.
This data depicts information about the kinds and distribution of linear glacial features
on the landscape.
Distribution Tile: USGS Quadrangle. Related Datasets: Glacial
Features - Point (glac<nnn>p), Surficial Geology (surf<nnn>), where <nnn>
represents the quadrangle ID number.
Currentness_Reference: publication date
Theme_Keyword: surficial geology
Theme_Keyword: glacial features
Place_Keyword: United States
Place_Keyword: New England
Place_Keyword: New Hampshire
Place_Keyword: Quad 166
Place_Keyword: CANDIA, NH
Use_Constraints: Not for legal use.
Contact_Organization: Complex Systems Research Center, University of New Hampshire
Attribute accuracy is tested by manual comparison of the source with hard
copy plots and/or symbolized display of the map data on an interactive
computer graphic system. Selected attributes that cannot be visually verified
on plots or on screen are interactively queried and verified on screen. In
addition, the attributes are tested against a master set of valid attributes.
Logical_Consistency_Report: Line topology exists.
Completeness_Report: Data is complete for the tile.
Digitizing RMS error of .002 feet or less. Spatial features verified by manual
comparison of the source with hard copy plots.
Originator: NH Department of Environmental Services
Title: Surficial Geologic Map of the CANDIA, NH Quadrangle
Publication_Place: Concord, NH
Publisher: New Hampshire Department of Environmental Services
Source_Contribution: Provided source for digitizing glacial features.
Field mapping procedure as follows:
Surficial geologic mapping represents a creative process of applying accepted models of glacial
erosion and deposition to the interpretation of direct observations of landscapes and landforms
in the field and representations of such features on topographic maps or aerial photographs.
Exposures of undisturbed material in active or abandoned gravel pits, road cuts, excavations for
building foundations, etc. provide critical data for mapping surficial geologic deposits and
material textures. Geologists supplement subsurface observations at these sites by digging
shallow holes with a shovel or extracting samples with a soil auger in areas that otherwise have
limited exposures. Interpretation of mapped glacial features is aided by additional sources of
information, including hydrography datasets and remotely sensed data such as aerial photographs.
The locations of bedrock outcrops are also mapped to identify the extent of thin surficial
materials, and to observe and record erosional features such as striations that indicate the
direction of ice movement. All data localities and map unit boundaries are plotted as accurately
as possible on a 1:24,000-scale topographic base map. Georeferenced water well data maintained
by the NH Geological Survey, mostly representing private domestic water wells drilled in bedrock,
are compiled for each map area. In particular, reported depths to bedrock and generalized
stratigraphic descriptions serve as a valuable adjunct to field observations.
Although the exact procedures may differ between individual mappers, the process generally begins
with an inspection of existing topographic maps and aerial photographs of the map area and surficial
geologic maps in adjacent areas. A reconnaissance or "windshield survey" of the landscape is then
conducted by driving as much of the road network in the map area as possible. Subsequent mapping is
conducted on foot, preferably taking advantage of improved visibility during 'leaf off" conditions in
the early spring and late fall. Map compilation is an ongoing process of refining and confirming
preliminary observations and fitting the field evidence within a conceptual framework of glacial
Some surface features exhibit a morphology that geologists readily recognize as diagnostic of a
specific mode of deposition. More commonly, however, depositional history must be reconstructed
by interpreting numerous observations within a local study area. This effort is guided by a
conceptual framework, generally known as the "morphosequence concept", that has been clearly
articulated by Koteff and Pessl (1981) in the now classic publication "Systematic Ice Retreat
in New England". To summarize:
"In the concept, a single sequence specifically refers to a continuum of
landforms composed of melt-water deposits, from more collapsed forms due
to melting of ice blocks at the head or upstream parts of outwash, to
progressively less collapsed forms downstream. A sequence can thus be
viewed as a body of stratified drift laid down, layer upon layer, by melt water
at and beyond the margin of a glacier, while deposition was controlled by a
specific base level. The complexity of the morphologic features depends on
the relative number, size, and distribution of detached ice blocks around and
over which the sequence was deposited."
The completed surficial geologic map thus represents a synthesis of all the field observations and
other site-specific data subject to the best professional judgment of the individual mapper.
Ultimately, the finished geologic map is the best representation of the surficial geology that can
be compiled from all of the data available at the time of publication. Limitations always exist
as a function of the scale of the map. Any map can be refined through the acquisition of new data,
especially data collected at a higher resolution that supports presentation at a larger scale. In a
sense, each surficial geologic map is a "progress report" on the evolving state of scientific
understanding of earth processes and events during the last deglaciation.
Contact_Organization: NH Department of Environmental Services - NH Geological Survey
Glacial features were digitized from source materials provided by NHDES
using a Calcomp Drawing Board III by Complex Systems Research Center (CSRC).
Edits were conducted on screen with guidance from NH Surficial Geologist,
Carl Koteff. Hard copy check plots, digital data and source materials were
sent to the NHDES for quality control. Final edits were made by CSRC as
directed by the NHDES.
Contact_Organization: Complex Systems Research Center
Contact_Person: GIS Database Manager
Contact_Position: GIS Database Manager
Address_Type: mailing and physical address
Address: Morse Hall, University of New Hampshire
Hours_of_Service: 8:30AM-5PM, EST
SDTS_Point_and_Vector_Object_Type: Complete Chain
Grid_Coordinate_System_Name: State Plane Coordinate System 1983
Digital data in NH GRANIT represent the efforts of the
contributing agencies to record information from the cited
source materials. Complex Systems Research Center, under
contract to the NH Office of State Planning, and in
consultation with cooperating agencies, maintains a
continuing program to identify and correct errors in these
data. OSP, CSRC, and the cooperating agencies make no claim
as to the validity or reliability or to any implied uses of