The summary of the knowledge possessed by the public, and the objects to which investigation might be usefully directed in these parts of Terra Australis, were as follow.  The outline of the north-west coast was known upon the authority, as generally believed, of Tasman; with some points corrected by Dampier.  The accuracy of Tasman’s chart was, however, very much called in doubt:  instead of being a continued shore, as the Dutch chart represented it, Dampier found the southern parts of De Witt’s Land to consist of a range of islands.  And he gives it as his opinion, that the northern part of New Holland was separated from the lands to the southward, by a strait; “unless”, says he, “the high tides and indraught thereabout should be occasioned by the mouth of some large river; which hath often low lands on each side of the outlet, and many islands and shoals lying at its entrance:  but I rather thought it a channel, or strait, than a river.”  This opinion he supports by a fair induction from facts; and the opening of twelve miles wide, seen near the same place by Vlaming’s two vessels, and in which they could find no anchorage, strongly corroborated Dampier’s supposition.

Later information had demonstrated, that the supposed strait could not lead out into the Great Ocean, eastward, as the English navigator had conjectured; but it was thought possible, that it might communicate with the Gulph of Carpentaria, and even probable that a passage existed from thence to the unknown part of the South Coast, beyond the Isles of St. Francis and St. Peter.

But whether this opening were the entrance to a strait, separating Terra Australis into two or more islands, or led into a mediterranean sea, as some thought; or whether it were the entrance of a large river, there was, in either case, a great geographical question to be settled, relative to the parts behind Rosemary Island.

If Tasman’s chart were defective at De Witt’s Land, it was likely to be so in other parts of the same coast; where there was no account, or belief, that it had been examined by any other person further north than the latitude 161/2 deg..  An investigation of the whole North-west Coast, with its numerous islands and shoals, was, therefore, required, before it could enter into the present improved systems of geography and navigation.

The chart of the West Coast, as far south as Rottenest, was founded upon much better authority; but for its formation from thence to Cape Leeuwin there were no good documents.  In this part, there was room even for discovery; and the whole coast required to be laid down with more accuracy than had been attainable by the Dutch navigators.