Why did Thomas Mitchell think there was an inland sea?

Answer 1

Observations by the early settlers indicated that Australia was very different from other continents, where rivers flowed to the ocean. Australia's rivers were very different from those of other countries, as the rivers all seemed to flow away from the ocean. Thus, it was assumed that they flowed from the Great Dividing Range, which runs down the entire eastern coast, to an enormous inland sea in the middle.

When John Oxley attempted to follow the Macquarie and the Lachlan Rivers, on two separate occasions, he did not realise it had been a typical flood year inland; so, when he came across marshes that overflowed the banks of the rivers, the logical assumption was that it was the beginning of an inland sea.

When Matthew Flinders circumnavigated the continent, he had already proven that Australia was a single continent, and not divided by a gigantic gulf, which had been one of the early theories. However, beliefs in an inland sea persisted because of the direction of the rivers, and the obstacles faced by Oxley. Mitchell was, in fact, sent to check the story of an escaped convict, Clarke, who had been recaptured. Clarke claimed that he had come across an enormous river that flowed to the northwest, which the natives called the "Kindur". Mitchell was sent to try and find this so-called river. He never found it, as no such river exists. Clarke is believed to have been lying in order to avoid being punished for escaping.

Incidentally, Mitchell did not believe in the theory of an inland sea. However, he did hope to find a river flowing to the Gulf of Carpentaria - again, something which does not exist.