Read the excerpt from "Save the Redwoods."

In the course of my explorations twenty-five years ago, I found five sawmills located on or near the lower margin of the Sequoia belt, all of which were cutting more or less Big Tree lumber, which looks like the redwood of the coast, and was sold as redwood. One of the smallest of these mills in the season of 1874 sawed two million feet of Sequoia lumber. Since that time other mills have been built among the Sequoias, notably the large ones on Kings River and the head of the Fresno.

What does the appeal in this excerpt mainly achieve?

It establishes the credibility of the