Complex sentence: He did some exploring, and traced the Gregory and Herbert rivers to their sources, and in August 1861 was placed in charge of an expedition to search for Burke and Wills, starting from the Gulf of Carpentaria.
Split into simpler sentences: He did some exploring, and traced the Gregory and Herbert rivers to their sources. In August 1861 he was placed in charge of an expedition to search for Burke and Wills, starting from the Gulf of Carpentaria.