SURFACES Surloces should be so shoded os to present a pleasing, even tone. In stroto charts the layers should be so shoded as to be easily distinguished. The weight and spocing of the lines and dots of the shading ore important; both should be determined from a considerotion of the size of the areas to be shoded end amount of reduction intended Proiected surfaces may be indicated by lighter shoding of the some type as illustrated at the right.

THE FOLLOWING SHADINGS ARE SUGGESTED:

lal Block (solid) for generol use for purposes of emphosis. It should be used with discretion, however, and usually not for large oreos. In stroto charts the lowest layer should be the most importoni and therefore generally requires the heaviest shading (usually block).

Ibl Crosshotch Sfiodmg* of o relatively dork lone, is often used in place of block for large oreas. A light Crosshatch is often useful for small layers of o strata chart.

(c) Parallel Line Shading* may be used lor large or small surfoces. The lines should not porollel any opprecioble length of the curves end vertical or horizontal shading is not recommended as it may be confused with grid rulings.

(dl Doited Shading (pebbled or stippled) is particularly useful for narrow layers of a stroto chart.

6. SURFACE DESIGNATION. Lobels should generally be pieced entirely within their respective surfaces If the surface is too smoH to permit this, o lobel may be placed entirely outside ond related to the surfoce by meons of on arrow. Keys should not be used if direct lobielmg is possible. However, the spoce about labeU should be reduced as much OS possible to ovo<d loo great contrast.