The New Bedrock Geologic Map of Vermont and the Digital and STATEMAP Mapping Program

Geologic Map of the Tillotson-Haystack Area, by Wallace Bothner and Jo Laird, 1999

The New Bedrock Geologic Map of Vermont

Vermont Geological Survey (VGS) directed by Laurence Becker at the Agency of Natural Resources (ANR), United States Geological Survey (USGS), University of Vermont geologists and students, and geologists affiliated with other New England colleges have participated since the early 1980's in a cooperative venture to produce the new bedrock geological map of Vermont at a scale of 1:100,000. The bedrock map under production, the first complete map since 1961, will make available to the public a geological map based on work which incorporates the understanding of plate tectonic theory. Editors for the Vermont map are Nicholas Ratcliffe (USGS), Rolfe Stanley (UVM, posthumous), Marjorie H. Gale (VGS) and Peter Thompson (UNH). The one-degree sheets were compiled by Nicholas Ratcliffe (USGS), Rolfe Stanley (UVM), Barry Doolan (UVM), Charlotte Mehrtens (UVM), Norman Hatch (USGS), Douglas Rankin (USGS), Peter Thompson (UNH), Marjorie Gale (VGS), Jon Kim (VGS), and Greg Walsh (USGS). Greg McHone contributed data for the compilation of Mesozoic dikes. Editors N. Ratcliffe, M.H. Gale, and P. Thompson compiled the complete map, and prepared the map and cross-sections for scientific review. A draft was presented at the NE Geological Society of America meeting in Virginia in 2004. In 2006-2007 USGS cartographers digitized the hand-drafted/colored maps, correlation chart and description of map units in Adobe Illustrator. Cross-sections and a tectonic map were completed in August 2008. The map entered scientific review on August 25, 2008. The map will be published as four large sheets - 2 for the map and additional sheets for unit descriptions, correlation of units, cross-sections, and references. The map incorporates detailed field studies conducted over 25 years by more than 60 geologists, including many students mentored by R. Stanley, B. Doolan, and C. Mehrtens.

What is bedrock geology?
Bedrock is the continuous, solid part of the earth's crust that overlies the mantle ( a 2800 km thick dense layer surrounding the earth's core). Bedrock underlies surficial materials such as sand, gravel, glacial deposits, and soil, and in combination with these earth materials forms the foundation for plant and animal life. Bedrock includes igneous, sedimentary and metamorphic rock types. In Vermont, some of the bedrock is exposed at the surface, but most is hidden by surficial cover. Geologists observe the exposed rock types and structures (folds, faults, fractures) in the field, sample the rock for microscopic(petrographic), chemical, and geochronological studies, then use this information to develop a three dimensional picture of the underlying bedrock and to understand the depositional and deformational history of Vermont.

Most rocks originate as deposits of sediment along continental margins and in ocean basins, as volcanic extrusions, or as intrusive rocks at depth in the earth's crust. Rocks are usually folded, faulted, transported, metamorphosed, and form mountain belts at active plate boundaries during plate collisions. Rocks exposed at the surface are generally being eroded or destroyed slowly over time by wind, water and ice. All of these processes are evident in rocks of Vermont, and geologists use bedrock maps to understand the rocks and structures that are the record of more than one billion years of geologic time.

What is a bedrock map?
A bedrock geological map shows the type of intact, solid bedrock at or near the earth's surface. The map is used to predict the nature of the bedrock where it is obscured at depth or by surficial material. A bedrock map generally includes rock descriptions, age relationships (stratigraphic sequence), major and minor structural data, and other information which is collected in the field, analyzed in the laboratory, and used to portray a three dimensional picture of the rock on a two dimensional topographic base map. Geologists use a variety of lines, symbols, and text to convey this information in the form of a geologic map.

What is the STATEMAP Mapping Program

STATEMAP receives funds through an annual competitive grant process through the National Cooperative Geologic Mapping Program of the U.S.Geological Survey.

The State Mapping Advisory Committee, comprised of legislators, consultants, geologists, and mineral industry personnel, meets with the State Geologist to review the map program and make recommendations concerning the goals of this project. The products developed through the map program provide fundamental sources of data to town planners, environmental scientists, government agencies, consultants, archaeologists, educators, industry and the general public.

While a major program goal is production of the new printed format Bedrock Geologic Map of Vermont in four sheets at a scale of 1:100,000, Vermont continues to map areas at 1:24,000 to address scientific and societal issues. As new work is completed, Vermont is digitizing that information in GIS format. Bedrock and surficial geologic maps at a scale of 1:24,000 are digitized and made available for release quickly on-line and/or as paper copy.

Why are we mapping the bedrock and surficial geology?

Vermont has a reputation for strong environmental programs and a philosophy which requires careful, planned growth. These programs have evolved such that the emphasis today is on protection rather than clean-up, planning rather than providing after-the-fact solutions. The geological environment is the host for Vermont's mineral and groundwater resources, as well as a receptor for contaminants. Providing easy access to current geological information is critical to the continued success of Vermont's environmental and growth-planning mission.

Vermont has produced abundant quality granite, marble, slate, talc, and asbestos as well as a variety of ores (copper, lead, sulphides) extracted during the nineteenth and early 20th centuries. Talc, the State Mineral of Vermont, and the three State Rocks-granite, marble and slate -continue to be marketable, high quality resources. Vermont rocks offer complex structures and chemistries which are being further defined and, in some instances, revealed for the first time by the new maps being produced.

There are areas in Vermont of more concentrated population growth and development where issues of water supply and wastewater are critical.. The availability of new geologic digitized maps will not only answer significant questions of geologic history, but can also be applied to managing resources and balancing the impact of human activity with protection of the environment.

Geology is an important layer of information that is applied to interpretations of environmental conditions both in the planning and problem solving stage. One can think of geology as being the base layer, and that understanding begins from the bottom up with a geological interpretation of regional and/or site conditions.

Which maps are available?
Digital maps available are listed at Digital Open File Reports and Open File Reports. Images are posted on Maps-On-Line. Other maps are available as USGS publications.

Maps are sold through the VGS and are listed in the publications catalog.
Please visit the Vermont-USGS Cooperative Geologic Mapping Project Website.
For other geologic maps, please visit the National Geologic Map Data Catalog.

Site maintained by: marjorie.gale@state.vt.us , updated 8/26/2008