U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES DDS-9
 
                           National Geophysical Data Grids:
                    Gamma-Ray, Gravity, Magnetic, and Topographic
                       Data for the Conterminous United States
                                           
                                           
                                          by
                                           
                                 Jeffrey D. Phillips
                                   Joseph S. Duval
                                         and
                                 Russell A. Ambroziak

                            ------------------------------

 This directory contains information and grids contained on and derived from
  the above CD-ROM

  ----------------

  Contents of the following ASCII info files:

    overview.txt - general info of CD-ROM contents (PC software not available
                      in this directory)

    grids.txt    - details of gridded data formats and content 

  ----------------

  Contents of the following grid directories under GRIDS:

    ODDF      - in-house binary format used by the USGS/GD/MRP 

    PC_binary - in-house binary format contained on CD-ROM

    ARC_INFO  - arc-info e00 format files (compressed with gzip)

    GXF       - ASCII grid exchange format (associated with Geosoft
                                            & compressed with gzip)

    Geosoft   - binary format used by Geosoft OASIS montaj

    grid_xyz  - ASCII grid point output in longitude, latitude, field
                (NAD27/Clarke 1866 , compressed with gzip)


  Short explanations of grid contents:

  bouguer.*  - complete Bouguer gravity anomaly at 2.67
  isograv.*  - isostatic residual gravity anomaly 30km,.35 g/cc
  magnetic.* - magnetic anomaly at original flight specs
  topo.*     - conterminous US topography
  topobaty.* - conterminous US plus offshore topography
  usak.*     - Potassium concentrations
  usath.*    - Thorium concentrations 
  usau.*     - Uranium concentrations

------------------


  Contents of the METADATA directory:

    FGDC compliant metadata files for two purposes:

      *_SDD   - files generated for Spatial Data Distribution website
      *_DDS-9 - files generated from cdrom DDS-9