+39.  Reproduction of the Thought of a Paragraph.+—­Our ability to reproduce the thought of what we read will depend largely upon our ability to select the topic statements.  In preparing a lesson for recitation it is evident that we must first determine definitely the topic statement of each paragraph.  These may bear upon one general subject or upon different subjects.  The three paragraphs on page 67 are all concerned with one subject, the uses of rivers.  A pupil preparing to recite them would have in mind, when he went to class, an outline about as follows:—­

General subject:  The uses of rivers. 
  First topic statement:  The fertility of flood plains is improved by
    irrigation. 
  Second topic statement:  Streams are the easiest routes of travel and
    commerce. 
  Third topic statement:  Man is indebted to streams for beauty of scenery.

While such a clear statement is the first step toward a proper understanding of the lesson, it is not enough.  In order to understand thoroughly a topic statement, we need explanation or illustration.  The idea is not really our own until we have thought about it in its relations to other knowledge already in our possession.  In order to know whether you understand the topic statements, the teacher will ask you to discuss them.  This may be done by telling what the writer said about them, or by giving thoughts and illustrations of your own, but best of all, by doing both.  It is necessary, then, to know in what way the writer develops each topic statement.

Read the following paragraph:—­

The most productive lands in the world are flood plains.  At every period of high water, a stream brings down mantle rock from the higher grounds, and deposits it as a layer of fine sediment over its flood plain.  A soil thus frequently enriched and renewed is literally inexhaustible.  In a rough, hilly, or mountainous country the finest farms and the densest population are found on the “bottom lands” along the streams.  The flood plain most famous in history is that of the river Nile in Egypt.  For a distance of 1500 miles above its mouth this river flows through a rainless desert, and has no tributary.  The heavy spring rains which fall upon the highlands about its sources produce in summer a rise of the water, which overflows the valley on either side.  Thus the lower Nile valley became one of the earliest centers of civilization, and has supported a dense population for 7000 years.  The conditions in Mesopotamia, along the Tigris and Euphrates rivers, are similar to those along the lower Nile, and in ancient times this region was the seat of a civilization perhaps older than that of Egypt.  The flood plains of the Ganges in India, and the Hoang in China, are the most extensive in the world, and in modern times the most populous.  The alluvial valley of the Mississippi is extremely productive of corn, cotton, and sugar cane.

—­Dryer:  Lessons in Physical Geography.