We heard, on Thursday last, of a most melancholy accident, which occurred in the Wolf Pen district, late last Thursday evening.  A Mr. MILLER, who lived near Miller’s Chapel, was working in his field, when seeing a dark cloud arising, supposed there was a heavy rain close by.  He unhitched his mules from the plow and mounted one of them, taking up his little son behind him.  The mule became frightened and threw Mr. Miller off, but not the boy.  In a short while the little fellow fell, but unfortunately his feet became entangled in the traces and held him.  The poor child was literally dashed to pieces against the ground.  This is a distressing affair.