Sixths are much like thirds in that they can be used to complement a melody, in fact the interval of a sixth is actually the inversion of a third. Notice that the thirds in the previous two exercises (the top notes) are now played an octave lower at the distance of a sixth below the melody.
Here is a melody harmonized in sixths, accompanied by open string bass notes.
This next piece is a medley of the Caribbean songs "The Banana Boat Song" (Day O) and "Jamaica Farewell". It is in the key of D Major and therefore uses Drop D tuning to enable an alternating bass accompaniment. This arrangement is a typical example of a melody harmonized in thirds and sixths.