As with most of the book, a great deal of the chapter is given over to describing the scene in which the action takes place.  The second paragraph reads as follows:

I had crossed a marshy tract full of willows, bulrushes, and odd, outlandish, swampy trees; and I had now come out upon the skirts of an open piece of undulating, sandy country, about a mile long, dotted with a few pines and a great number of contorted trees, not unlike the oak in growth, but pale in the foliage, like willows. On the far side of the open stood one of the hills, with two quaint, craggy peaks shining vividly in the sun.

Stevenson is brilliant in his description, and it runs through the rest of the chapter.  Each time an event takes place, he takes care to describe the way things look, the sounds of the action, etc.

Another element of the chapter is simply the way that everything is told from Hawkins perspective, which gives the terror of it a far more connective ability with the reader.  The reader feels themselves in the place of Hawkins as he cowers in the bush watching Silver kill Tom.