The great topographic map of the United States now being thus prepared by the Survey, is published in atlas sheets of aproximately uniform size, 16% by 20 inches, on which the mapped area occupies a space inches in height, and IPA to 16 inches in width according to the latitude. The division of land repre sented by an atlas sheet is called a °quadrangle? and is always bounded by parallels of altitude and meridians. Although the sizes of the sheets are always the same, three different scales are employed in the mapping of the surveyed in order to serve different purposes and to suit various conditions. A scale of 1: 62500, very nearly one inch to one mile, is used for map ping the thickly settled, or industrially import ant sections of the country. The sheets on this scale cover an area of 15' of latitude by 15' of longitude. A scale of 1: 125000, nearly one inch to two miles, is used for mapping the greater part of the country. The sheets on this scale cover an area of 30 of latitude by 30' of longitude. A scale of 1:250000, very nearly one inch to four miles, is used for mapping the desert regions of the western States, and gives sheets which include an area of 1° of latitude by 1° of longitude.
This map is printed in three colors and shows the following named classes of natural and artificial features: (1) Water, including seas, lakes, ponds, rivers, creeks, canals, swamps, etc., are shown in blue. (2) Relief, including mountains, hills, valleys, cliffs, etc., are shown in brown contours. (3) Culture, or the works of man, such as villages, towns, cities, roads, rail roads, boundary lines, etc., are shown in black. The features shown in blue and black are self explanatory. In the case of the brown contour lines, each contour passes through points which have the same altitude above mean sea level, and a series bf such lines arranged one above the other at regular vertical intervals, but ap pearing on the map at irregular intervals, that is, close together where the slopes are steep, and far apart where the slopes are gentle, ac curately delineates the general configuration of the country, and gives the elevations of all points above the level of the sea. The vertical interval adopted varies according to the char acter of the country mapped. In a flat country it may be as small as 10 feet, while in a moun tainous region it may be as large as 200 feet. usually, every fifth contour is made heavier than the others, and is figures giving its elevation above the level of the sea. The heights of many other points, such as the intersections of ordinary roads and highways, railroad crossings and stations, the summits of uplands, hills and mountains, and definite bench marks, are also given in figures which are placed close to the points to which they refer, and are correct to the nearest foot. Each sheet is designated by the name of a principal town, or the name of some prominent natural feature within the district represented, and the names of the adjoining published sheets are printed on the margins. Explanations of the various con ventional signs used are printed on the back of each sheet, and materially assist in the reading of the map.
This topographic map is the base on which the facts relating to the geology and the min eral resources of a quadrangle are represented, and constitute the sheets of the Geologic Atlas of the United States published by the Survey.
The price of the topographic sheets is five cents each when the number purchased is less than 100 copies, and two cents each when they are ordered in lots of 100 or more copies. In the Geologic Atlas the topographic and the geologic sheets of a quadrangle are bound to gether, and, accompanied with a textual de scription of the district represented, constitute a folio of the Atlas. These folios are sold for 25 cents each, except those that have received special treatment and are unusually comprehen sive. The price of such varies according to the character of the information afforded, the num ber of the maps in the folio, etc. All com munications relative to these maps, or any other publication of the Survey should be addressed to The Director, United States Geological Sur vey, Washington, D. C.
The accompanying map is a small portion of the Housatonic quadrangle which includes por tions of Massachusetts, New York and Con necticut. It affords a general idea of the topo graphical treatment; but, being printed only in black and white, it fails almost completely to give a true idea of the actual beauty of the original sheet as printed in the three conven tional colors already described.
The importance of the topographical and geological publications of the Survey cannot be overestimated. The maps form the basis of all the State and county maps of the United States published for commercial purpose. Their accuracy is such that they are readily available for use in connection with the preliminary work of railroad, canal and other surveys, and for purposes of verification in damage suits and other legal proceedings before the various tribunals.
It is true that the work of the survey costs the government hundreds of thousands of dol vey set the standard for this country and are invaluable not only to the student-engineer, but also to the actual worker in the field. These publications may be obtained by application to the Director of the Survey at Washington, D. C. Consult Branner, J. C., 'The relations of the State and National geological surveys to each other and to the geologists of the country' (Salem 1890) Johnson, D. W., 'Field methods in physiographic geology' (Lancaster 1913) ; Lesley, J. P., 'The utility of government geolog ical surveys' (Philadelphia 1874) ; Hayes, C. W., 'The State geological surveys of the United lars annually, hut the returns through the vari ous industrial channels and through the develop ment of the natural resources of the county, amounts to hundreds of millions.
• This is especially the case relative to the work and publications of the Geologic Depart ment, without which the high economical de velopment of the mineral resources of the country would be practically impossible.
In the matter of the use of instruments, such as the plane table, stadia and tape, and in the application of precise but rapid methods in the execution of the particular class of surveying practised, the various publications of the sur (Washington 1911) ; Wood, G. M., The principal faults found in manuscript submitted for publication by members of the United States Geological Survey) (Washington 1906).