Complex sentence: Due to the success of the coal mines Halliday began to purchase property in the area to search for oil, but was unsuccessful in locating oil deposits but was successful in locating one of the most productive salt mines in the region.
Split into simpler sentences: Due to the success of the coal mines Halliday began to purchase property in the area to search for oil. He was unsuccessful in locating oil deposits but did find one of the most productive salt mines in the region.