'ED STATES 
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gradually away and forms an inclined table-land tha 
versed by a few shallow gullies* On the map each < 
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is represented, directly beneath its position 
sketch, by contour lines. 
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The contour interval, or the vertical distance in feet t 
one contour and the next, is stated at the bottom of eac 
This interval differs according to the topography of tl 
mapped; in a flat country it may be small as 1 foe 
mountainous region it may be as great as 250 feet. ' 
contour lines, every fourth or fifth one, are made heavk 
the others and are accompanied by figures showing a 
The heights of many points—such as road corners, si 
surfaces of lakes, and bench marks—are also given on t 
in figures, which show altitude! to 1 
lat exact altitudes- 
the nearest foot only, 
those of bench marks—as well as the £ 
coordinates of triangulation stations, ate published in b 
that are issued free by the Geological Survey. j 
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The lettering and works of man are shown in black. I 
daries, such as those of a State, county, city, land 
township, or reservation, are shown by continuous or 
lines of different kinds and weights. Metaled roads are 
by double lines, one of which is accentuated. Other 
roads are shown by fine double lines, private’and poo: 
by dashed double lines, trails by dashed single lines. 
Each quadrangle is designated by tlie name of the pi 
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