Page:The Journal of geology (IA journalofgeology21894univers).pdf/105

anced relations of carrying power and load involved in the explanation of the growth of delta may not be perceived unless it is carefully discussed in making out the scheme of river development. There can be no thoroughness of work where observation and explanation are slurred over or confused. After observation and description are well advanced, explanatory terms may be introduced; it then being seen that such terms imply a pairing off of observed facts with the appropriate members of the deductive scheme. This mental process must become perfectly conscious; its several steps must be recognized in their proper relations. No strong grasp of the subject can be gained until the student sees clearly where every part of the work stands in relation to the whole.

Topographical maps published by the U. S. governmental bureaus.—It is difficult to secure a full series of facts for laboratory study. My plan at present is to select maps from our own surveys and from the surveys of foreign countries, with little regard to locality, but with much regard to geographical features. The charts of our coast survey offer admirable illustrations of litoral forms. For example, the sand-bar cusps of Capes Hatteras, Fear, and Lookout, and their off-shore shoals, all formed between back-set eddy currents, rotating betwixt the Gulf stream and coast; or the blunted Canaveral cusp on the Florida coast, and its southward migration from a former position; or the fjords and islands of Maine; the sounds of North Carolina; the delta of the Mississippi, a geographical gem.^[1] The maps of the Mississippi River Commission offer remarkable illustrations of the behavior of a large river on its alluvial plain. Its meanders, its cut-offs, and its ox-bow lakes are shown to perfection. The eight-sheet map of the alluvial basin of the Mississippi, prepared by this commission, can be had for a merely nominal charge; it exhibits the lower part of the great river in an admirable manner. It tells the curious story of streams that descend from the eastern bluffs,