A drawing that is to be reproduced by photolithography should be made on pure-white paper in lines, dots, or black masses with black waterproof ink. It should be one and one-half to two or three times the size of the finished print. Photolithography is particularly adapted to the reproduction of maps, plans, and other large drawings. Within certain limitations, lines may be changed and details may be added after proofs have been submitted. The process is ordinarily used for reproducing illustrations in one color (black), but it is used also for printing in more than one color, generally over a black outline base, each color being printed from a separate stone, as in chromolithography. OFFSET PRINTING. In the offset process the design is "offset" from a lithographic plate or stone to a rubber blanket on a cylinder, from which it is printed. By thus obtaining an impression from an elastic surface the finest details can be printed on rough, uncoated paper, which can not be used in other processes, which can be folded without danger of breaking, and which is more durable than coated paper. Plates II, III, IV, VII, and VIII in this pamphlet were printed by this process. CHROMOLITHOGRAPHY. The chromolithographic process, by which illustrations are printed in color from stone, is used in Survey publications principally for reproducing geologic maps, but it is sometimes used for reproducing colored drawings of specimens. There are several kinds of color printing from stones. One produces a picture by superimposing colors that combine and overlap without definite outlines and thus reproduce the softly blended colors of the original. Another reproduces the original by printing colors within definite outlines on a "base" which has been previously printed in black. The first kind is used by the Survey for reproducing colored drawings of specimens. The second is followed in reproducing geologic maps.