), brick-red or etruscan red; Algonkian (A), terra cotta or onion-skin pink; Archean (
), gray-brown or drab.[9]
[9] Names printed in italic are from "Color standards and nomenclature," by Robert Ridgway.
REDUCTION OF ENLARGEMENT OF MAPS.
The following is the simplest and most accurate method of marking the reduction or enlargement of a map to a selected scale: Measure the distance between the extreme meridians along one of the parallels. (See [fig. 10].) Convert this distance into miles by multiplying the number of degrees it covers (say 3) by the number of miles in a degree. A degree on the forty-third parallel, for example, is 50.669 miles, [10] which multiplied by 3 equals 152.007 miles. Then draw a line on the margin of the map, outside the border, the exact length of the 3 degrees, and just below this line draw another line representing the same number of miles (152.007) on the scale to which the map is to be reduced or enlarged. Then mark to reduce or enlarge the upper line to the lower line, as shown in [figure 10]. A long line will reduce error and give greater accuracy than a short one, and therefore as great a distance should be set off as possible. The number of miles represented by both lines and the fractional scale to which it is to be reduced should be stated on the drawing, for permanent record.
[10] See U. S. Geol. Survey Bull. 650, p. 37. 1916.
Maps that will bear reduction without affecting the clearness of the details they show may be reduced to fit the book in which they are to appear, regardless of definite scale. The reduction for such maps is best marked in fractions, as "1/2 off," "1/3 off," "2/3 off." If the size needed is not exactly represented by these fractions it should be indicated in inches, as "Reduce this line to 71/2 inches," or "Reduce to 43/8 inches in width."