Page:The Journal of geology (IA journalofgeology21894univers).pdf/107

new package of these maps brings some new illustration, which is put in use as soon as opportunity allows. One of the latest is a peculiar case in Southern California: a number of small rivers are here seen running down from the Coast range to the shore of the Pacific; but their mouths are all shut up by sand-bars in the most summary manner! A curious trick for a Pacific ocean to play on some trifling little streams that one would think were beneaths its notice.

These maps are simply indispensable. They call forth much interest from the class. At first hardly translatable into words, their meaning grows plainer and plainer, until at the close of the course they are as suggestive as they were uncommunicative at the beginning.

Foreign topographical maps.—Not less valuable and far more accurate than our own topographical sheets are those of various foreign topographical surveys. Unfortunately the relief in most of these is expressed by hachures; altitudes being given only for occasional points, or by widely separated countour lines; but the general expression of the surface is certainly admirably rendered in many of the surveys. The older maps are generally too heavily burdened with hachures; but the more modern surveys are very artistically executed. It has been my practice for several years past to select certain groups of sheets from the sets of foreign topographical maps in our college library, and order extra copies of these groups, mount them on cloth and rollers, and thus prepare them for the most convenient use in the laboratory. Both the library and laboratory collections of this kind are increasing year by year, and I shall soon prepare a special account of the grouped sheets, in the hope that others may perceive their great value and introduce them as teaching materials as far as possible. Without specifying all that have been thus far secured, I may briefly mention some of the more interesting examples.

From the Army Staff map of France (1:80,000) there is a group of sheets showing the level plain of the Landes, with its exceptionally straight shore line and its wide belt of litoral sand