In the story 'The River' by Mark Twain, he uses an extended metaphor, comparing the Mississippi river to books, art, and poetry. In ‘reading the river’ the pilot’s rigorous study of the river is referred to, Twain regard this as reading a book.
“The face of the water in time became a wonderful book- a book that was a dead language to the uneducated passenger but which told its mind to me without reserve, delivering its most cherished secrets as clearly as if it uttered them with a voice.”
In the above line, Twain compares water to the book. The sight of the pilot is compared to that of passenger’s is another extended metaphor used. He compares it with “italicized passages”, “shouting exclamation points” and the “pretty pictures". To the pilot’s eye, such features of the river becomes the language of water. However, how the river is being read as a book depends upon one’s experience who is reading, as it can have different meanings.