the other two named the Nera and the Teverone; that the Tiber delta has been prograded about fifteen kilometers from the original river mouth at the outer side of the volcanic saddle; and so on. Thus at the end of eight or ten minutes, the hearers will be well prepared for any details that may follow; details, for example concerning various smaller calderas in the truncated volcanic cones; or concerning the meanders of the Tiber; or concerning the origin of the cascades at Tivoli by travertine aggradation at the mouth of a formerly normal and mature valley in the limestone range east of Rome. Each detail will fall easily into place, and take proper rank among its fellows.
When it is remembered that, however accurately the features of a region may be known to the geographer who has studied them on the ground, they can—apart from maps—become known to those who have not been on the ground only through such report as the observer may give concerning them, it will be recognized that the attention here directed to the art of presentation as a supplement to the science of investigation is fully deserved.
Printed Reports.—If allowance is made for the necessary contrasts between oral and printed presentation, as summarized at the beginning of this supplement, the suggestions given above as to the different styles of presentation for reports on geographical problems may apply to printed essays in scientific journals, as well as to spoken communications made at scientific meetings: but there are certain additional features of printed reports, especially if they are long and detailed, which deserve consideration. In preparing such reports, it must be borne in mind that an enormous amount of printed matter is issued in these modern times; and that even within the limits of a single science there is much more material published than can possibly be read by any one man. Hence if the author of an essay desires to increase his chance of gaining the attention of his colleagues, he ought to give particular attention to making his text easily intelligible. Several recommendable means of realizing this object may be briefly stated.
In long and detailed essays, it is extremely helpful to the reader to find a summary of contents presented in an introductory paragraph. The value of such a summary here is much the same as at the beginning of an oral report: it enables the reader, when he comes to the later pages, to perceive the bearing of each part on the whole. A summary at the end of an essay by no means takes the place of one at the beginning; for the author who places a summary only at the end of his report evidently regards that as the proper place for its reading; and hence prepares it in a style which may be easily understood at the end of the article, but which is necessarily quite unlike the style of an opening summary that is to be read as an introduction to everything that follows. Two summaries, one at the beginning in proper introductory phraseology, and one at the end in much more specialized phraseology,