Man oh man, that wispy grass is rendered every bit as powerfully as those oxen.
The legend is that Sickles taught cartoonist Milton Caniff how to draw in this high contrast chiaroscuro style. Caniff continued to employ this style effectively for another fifty years on his famous comic strips Terry and the Pirates and Steve Canyon. Sickles, on the other hand, quickly abandoned this approach and went on to do other things.
Many years later, Sickles briefly revisited chiaroscuro for this drawing. After all those years, he still remained the master.
