So long as a geologist is in the field for a short and continuous period and in a restricted and comparatively simple district, no more elaborate and systematic system of notes is needed than is afforded by a map and a book. But when the district becomes complex and difficult, as in many metamorphic areas, and when the field work extends through several seasons, often with intervals of a year or two between, some method of indexing and compiling becomes absolutely necessary. The best of memories can not carry the endless details involved, and during office work time can not be spared for the discouraging search through a number of note books. A system that will work almost automatically is as essential to the geologist as is double-entry book-keeping to a large commercial house, and it fills very much the same field.
If, moreover, a teacher has to give . . .