Complex sentence: Dawson Letter Books Between 1878 and 1880 twenty five bonded convict's whose contracts were sold to the Comer backed Eureka mines died and their bodies were dumped into shallow earthen pits on the edge of the mine site.
Split into simpler sentences: Dawson Letter Books Between 1878 and 1880, twenty-five bonded convicts whose contracts were sold to the Comer-backed Eureka mines died. Their bodies were dumped into shallow earthen pits on the edge of the mine site.