or geologic survey of the country on an excessively elaborate plan.  Over much of this area the sheets of the map will also be constructed on a scale of 1-250,000, but in special districts that scale will be increased to 1-125,000, and in the case of important mining districts charts will be constructed on a much larger scale.  In the eastern portion of the United States two scales are adopted.  In the less densely populated country a scale of 1-125,000 is used; in the more densely populated regions a scale of 1-62,500 is adopted, or about one mile to the inch.  But throughout the country a few special districts of great importance, because of complex geologic structure, dense population, or other condition, will require charts on still larger scales.  The area of the United States, exclusive of Alaska, is about three million square miles, and a map of the United States, constructed on the plan set forth above, will require not less than 2,600 sheets.  It may ultimately prove to require more than that, from the fact that the areas to be surveyed on the larger scale have not been fully determined.  Besides the number of sheets in the general map of the United States, there will be several hundred special maps on large scales, as above described.

Such is a brief outline of the plan so far as it has been developed at the present time.  In this connection it should be stated that the map of the United States can be completed, with the present organization of the Geological Survey, in about 24 years; but it is greatly to be desired that the time for its completion may be materially diminished by increasing the topographic force of the Geological Survey.  We ought to have a good topographic map of the United States by the year 1900.  About one-fifth of the whole area of the United States, exclusive of Alaska, has been completed on the above plan.  This includes all geographic work done in the United States under the auspices of the General Government and under the auspices of State Governments.  The map herewith shows those areas that have been surveyed by various organizations on such a scale and in such a manner that the work has been accepted as sufficient for the purposes of the Survey.

Much other work has been done, but not with sufficient refinement and accuracy to be of present value, though such work subserved its purpose in its time.  An examination of the map will show that the triangulation of the various organizations is already largely in advance of the topography.  The map of the United States will be a great atlas divided into sheets as above indicated.  In all of those areas where the survey is on a scale of 1-250,000, a page of the atlas will present an area of one degree in longitude and one degree in latitude.  Where the scale is 1-125,000, a page of the atlas-sheet will represent one-fourth of a degree.  Where the scale is 1-62,500, the atlas-sheet will represent one-sixteenth of a degree.  The degree sheet will be designated by two numbers—­one representing latitude, the other longitude.  Where the sheets represent fractional degrees, they will be labeled with the same numbers, with the addition of the description of the proper fractional part.