In many parts of the Arid Region there are extensive deposits of coal. These coal fields are inexhaustible by any population which the country can support for any length of time that human prevision can contemplate. To withhold from general settlement the entire area of the workable coal fields would be absurd. Only a small fraction will be needed for the next century. Only those lands should be classed as coal lands that contain beds of coal easily accessible, and where there is a possibility of their being used as such within the next generation or two. To designate or set apart these lands will require the highest geological skill; a thorough geological survey is necessary. In providing for a general classification of the lands of the Arid Region, it will, then, be necessary to recognize the following classes, namely: mineral lands, coal lands, irrigable lands, timber lands, and pasturage lands. The mineral lands are practically classified by the miners themselves, and for this no further legal provision is necessary. The coal lands must be determined by geological survey. The work of determining the areas which should be relegated to the other classes--namely, irrigable, timber, and pasturage lands--will be comparatively inexpensive. CHAPTER III. THE RAINFALL OF THE WESTERN PORTION OF THE UNITED STATES. The Smithsonian Institution conducted for a number of years an extensive system of measurements of rainfall in the United States, and at the same time diligently collected pluvial records from every possible source. The accumulated data thus collected were placed in the hands of Mr. Charles A. Schott for reduction and discussion, and he prepared the “Smithsonian Tables of Precipitation in Rain and Snow”, which appeared in 1868. Since that time much additional material has been acquired by the continuation of the work to the present time, and also by a great increase in the number of observation stations, and so valuable is this new material that it has been determined to recompile the tables and issue a second edition. By the time the present report was called for, the preliminary computations for the tables had developed an important body of facts bearing on the climate of the Arid Region, and through the courtesy of Prof. Joseph Henry, Secretary of the Smithsonian Institution, and of Mr. Schott, they were placed at my disposal. Mr. Schott also made such a change in the order of computation as to give precedence to the states and territories which form the subject of this investigation, and by this timely favor made it possible to base the following discussion on the very latest determinations of rainfall.