Read the passage below from "Save the Redwoods" by John Muir.
In these noble groves and forests to the southward of the Calaveras Grove the axe and saw have long been busy, and thousands of the finest Sequoias have been
felled, blasted into manageable dimensions, and sawed into lumber by methods destructive almost beyond belief, while fires have spread still wider and more lamentable ruin. 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. The destruction of these grand trees is still going on.
What type of text structure is Muir using in this paragraph?