To prepare a drawing that will be in every way suitable for reproduction usually requires experience of a kind not acquired in many other kinds of drafting, such as preparing engineers' or architects' drawings, because the drawings themselves or blue prints made directly from them are the things the engineer or the architect desires. Drawings prepared for reproduction are generally made larger than publication size, and it is therefore necessary to gage each line, letter, or feature for a definite reduction. Engineers' and architects' drawings generally do not require preparation for reproduction by any process, but in preparing illustrations for the reports of the Geological Survey reproduction must be fully considered at every step, and each drawing must be made according to the requirements of a certain selected process and gaged for a certain reduction. The draftsman should therefore know how to plan each drawing step by step for an engraved cut, a lithograph, a text figure, or a plate, always with a definite result in view. He should be familiar with processes of engraving and should know the special requirements of each process, and he should be able to prepare drawings for any specified reduction in a way to insure good, legible reproduction. The geologic draftsman should read and study such textbooks of geology as those of Dana and Geikie and should familiarize himself with structural geology, the geologic time divisions, and geologic nomenclature. He should be able to prepare a simple, effective illustration from complicated rough originals and to supply minor missing essential parts or features. To perform his work successfully he must possess mechanical skill and some artistic taste, as well as good eyesight and great patience. INSTRUMENTS. The following list of draftsmen's instruments is practically complete. Those which are considered indispensable are marked by asterisks; the others may be used according to individual preference. The same kind of instrument may be duplicated in different sizes according to the variation in the demands of the work.