area have been more humid (and the evaporation potential less) and would not have favored development of high selenium concentrations. Water and aquifer materials in the uppermost part of the aquifer have been most affected by the present-day arid climate and are characterized by chemically oxidizing conditions that favor high selenium solubility. Low selenium concentrations in some ground water near the trough of the valley (near P1) are probably due to the ground water's origin in eastern valley geologic materials that are naturally low in selenium. Thus, the highest selenium concentrations appear to have resulted from a combination of the leaching of selenium from saline soils by irrigation water and the subsequent evaporation of ground water. Greatly increased ground-water recharge brought about by irrigation and the installation of subsurface drains have combined to bring selenium-rich water to the land surface. Economical solutions to the agricultural drainage problem in the western valley may, in the future, be based on controlling the ground-water system so that the seleniumrich water is not brought to the surface. FEDERAL EXCHANGE FORMAT come unwieldy in terms of complexity and implementation costs. Thus, simplicity and flexibility became the primary design goals. Design of the prototype Federal Geographic Exchange Format was completed in fiscal year 1986, and testing is being The recent nuclear accident at Chernobyl Federal agencies in different parts of the conducted within and between many in the Soviet Union, together with the 1979 accident at the Three Mile Island nuclear plant in Pennsylvania, has focused national attention on how authorities might expedite the evacuation of citizens from an affected area. Ideally, authorities should have immediate access to information regarding the location of people within a threatened area, available transportation routes out of the area, weather patterns that influence radiation dispersal, and the direction and rate of possibly contaminated streamflow. Unfortunately, all the needed information is not found in a single, comprehensive data base, nor is it available in compatible data structures and formats. In order to merge different yet related types of data into a single data base for rapid computer analysis, all the various data elements must be uniform in structure for computerized handling. As a result of discussions concerning the exchange of digital cartographic information, the Office of Management and Budget created the Federal Interagency Coordinating Committee on Digital Cartography in 1983. Consisting of 27 Federal agencies and chaired by the Geological Survey, the committee was charged with the critical task of “developing and adopting, for use by all Federal agencies, common standards of content, format, and accuracy for digital cartographic data to increase its inter changeability and enhance its potential for multiple use." A first step toward meeting these standards is delineating the data structures and formats needed to facilitate the interagency exchange of computerized cartographic and geographic data (termed "spatial" data). The prototype Federal Geographic Exchange Format, developed by the committee, is such a step. In developing the format, the committee had to keep in mind several major areas of concern. First, the format chosen would have to accommodate existing spatial and earth-science data bases as much as possible to avoid costly reentry of data. Second, the format would have to be flexible enough to handle future spatial data base developments. Finally, the format should not be country. Hydrographic, topographic, geologic, hydrologic, demographic, administrative, navigational, transportation, land survey, soils, natural resources, and other types of data are all being used to test the this prototype testing is completed in 1987, capabilities of the exchange format. Once the Survey will be responsible for finalizing an operational version of the Federal Geographic Exchange Format, the ultimate goal being to make the format a Federal Information Processing Standard for the exchange of digital spatial data. Interest in the Federal Geographic Exchange Format has now gone beyond national bounds into the international arena, since the Federal Geographic Exchange Format might become the standard exchange format for a worldwide cartographic data base. Incidents such as the release of radiation that travels worldwide, unconstrained by political borders, strongly enforce the need for such an international data base and a standardized means of exchanging information. NEW MAP OF GLACIAL DEPOSITS PROVIDES DATA FOR LAND PLANNING DECISIONS A geologic map showing a threedimensional perspective of both surficial and subsurface unconsolidated deposits over much of the northern conterminous United States has been completed by the U.S. Geological Survey and is being prepared for publication. The map area is the region once covered by the thick continental ice. sheets in the United States east of the Rocky Mountains and in parts of Canada, the Great Lakes, and the Atlantic offshore (see fig. 2A for location of map coverage). The map shows the character of the surficial sediments, the total thickness of glacial, glacially related, and postglacial sediments, and certain well-mapped buried units. Figure 2. Map area and format for the map of the glaciated United States east of the Rocky Mountains. This map conveys, for the first time, the regional distribution and thickness of glacial and postglacial sediments, which previously had been shown in detail on local maps only. The data shown on the map were compiled and reinterpreted from approximately 850 existing maps, reports, and unpublished data sources. Discussions with geologic authorities for each State enhanced the quality of reinterpretation and map compilation. Most thickness data were taken from reports and drill hole logs and had not been published in map form before. Because a uniform classification system that could encompass differing styles of geologic mapping had to be developed for surficial units in the map area, many map patterns are different from those on existing maps. For example, the glacial history of New England is quite different from that of the Great Plains States, the result being contrasts in the glacial sediments and mapping emphases in the two regions. The uniform classification emphasizes similar aspects of the deposits in these areas and should, therefore, add to the effectiveness and accuracy of regional assessments. Portraying not only the surficial geology but also the nature and extent of geologic units in the subsurface, this map is in essence a three-dimensional view of the outermost layer of the Earth. A small portion of the map is shown in figure 2B. This area, located in southwestern Ohio, was covered by ice during at least two major glacial episodes. Before and between glaciations, a network of streams and valleys existed; the major river in that network flowed past Hamilton and Dayton, Ohio, roughly where the Great Miami River flows today. This ancient valley and its tributaries contain a major aquifer system that serves the area's industrial centers. When the most recent (late Wisconsinan) glacier flowed over the area about 21,000 years ago, most of the valleys were covered over with till, a poorly sorted ice-lain sediment; in many valleys, sandy river sediments were not removed by the glacier and today serve as aquifers buried beneath the till (fig. 2B). Sandy sediments in the major river valley commonly occur from the land surface down to bedrock, because this valley was the course through which water from the melting, retreating glacier was channeled. This map is the first regional approximation of the three-dimensional distribution of sediments over a very large area and is intended to supplement, not replace, the more detailed work on which it is based. Detailed mapping, particularly in populated areas, is necessary to address the site-specific geologic problems related to man's activities. at and beneath the land surface. Detailed mapping is also required to interpret the geologic history and framework of sediments for a region. Regional maps such as the one discussed here place local detailed mapping in a regional context, permit the extrapolation of data into unmapped areas, and depict large-scale regional geologic features that are beyond the scope of detailed local mapping. A regional map in many cases will point out a problem or relationship that is not apparent on a detailed map and thus permits information from the detailed map to be used correctly to solve problems arising from site-specific activities. Surficial geologic and sediment thickness mapping and the ability to predict where buried aquifers occur are vital tools for solving problems such as the siting of landfills and construction, the evaluation of mineral resources, and the evaluation of ground-water resources and their vulnerability to contamination. Approximately 40 percent of the population in the conterminous United States resides within the region covered by the map, which is less than 25 percent of the total area of the country. Population density this high necessitates regional cooperation, across State and other political boundaries, in planning and in assessing problems involving waste disposal and ground-water management, since the waste of one community can unintentionally contaminate the drinking water of another. Information on the map indicates the thickness of the unconsolidated sediments (which contain numerous aquifers) and also the extent of certain major aquifers; this information can be used to supplement detailed mapping in predicting contaminant movement through the unconsolidated sediments. The thickness and composition of these sediments may also influence the generation and migration of radon gas and mitigate the effect of acid rain. In addition to its applications for resources and land planning, this new map should help to stimulate research and more detailed three-dimensional mapping. For example, research focusing on the creation of a digital geologic data base from the map is underway. Subsequent analysis of the digital data will permit the production of computergenerated derivative maps that will combine the geologic data base with hydrologic, cultural, and other data sets. These derivative maps will deal with a broad spectrum of topics including basic research into glacial mechanics and history, regional relations between glacial deposits and hydrology, and the need for applying geologic data to land use, waste disposal, and ground-water management decisions. HYDROCHEMICAL RESPONSE OF A SMALL STREAM IN THE SOUTHEAST TO A RAINSTORM The hydrologic response and the spatial and temporal patterns of stream chemistry were used to identify several key processes regulating stream acidification and major ion chemistry in a 100-acre research watershed (fig. 3A) at the Panola Mountain State Conservation Park near Stockbridge, Ga., |