How does the author use imagery in the novel, The Tamarack Tree?

Examples of imagery:

Between the towns I saw miles of cotton plantations, with Negroes working in the fields under the hot sun. Some of them would straighten up as the steamer went by, sometimes waving, at other times, just staring for a moment before bending again to their work. Fieldhands, Derry told me. I gazed after them for a long time. pg. 8

Van Dorn's thirty-five hundred Confederate horsemen gathered in the woods that surrounded the place and waited quietly for dawn. Then, with the terrifying scream known as the rebel yell, they swept into Holly Springs from every direction. They torched the ammunition dumps, the trains and storage sheds, and the provision depots, rounding up and capturing most of the men who were intended to defend the place. pg. 111

Some were at the dock to unload the ship, their skin like polished ebony, shining with perspiration; some drove smart carriages, sitting very straight in the front while their white employers in the back protected themselves with parasols or wide straw hats; some were white-kerchiefed maids accompanying their mistresses on shopping expeditions. pg. 6