Conversation so far:
What was Thomas Mitchell exploring during his fourth expedition?
Thomas Mitchell was convinced that a significant river must flow north-west into the Gulf of Carpentaria, this being the main thrust of the endeavour.
Was Thomas Mitchell correct in believing a significant river must flow north-west into the Gulf of Carpentaria?
Thomas Mitchell's second-in-command Kennedy proved beyond doubt that the Victoria did not continue north-west, but turned south-west and joined Cooper Creek.
When did Thomas Mitchell begin his explorations during his fourth expeiditon?
On 15 December 1845.
Who else was Thomas Mitchell with during the exploration party of the fourth expedition?
Mitchell started from Boree with a large party including Edmund Kennedy as second in command.
Did anything interesting happen during Thomas Mitchell's fourth expedition?
Mitchell followed the Balonne to the Maranoa, and the Cogoon to a magnificent pastoral district in the midst of which stood a solitary hill that he named Mount Abundance.
Why did Thomas Mitchell call the solitary hill Mount Abunance?
Mount Abundance was named by Thomas Mitchell on 7 May 1846 because of the abundance of pasture in the area.

Question: How long did the expedition last?
Self-contained rewrite: How long did Thomas Mitchell's fourth expedition last?