The Oxley Highway roughly follows his route from Coonabarabran to Port Macquarie.

Councils and other groups have organised parades and re-enactments of his trek.

When Blaxland, Lawson and Wentworth found a way across the Blue Mountains in 1813, surveyor, George Evans was sent to explore the hinterland.

He discovered the Macquarie River at Bathurst and noted it flowing north-west. Returning in 1815, Evans discovered the Lachlan River flowing west. Speculation followed about a possible inland sea.

In 1817 Governor Macquarie instructed the surveyor-general, John Oxley, to follow the Lachlan to the inland sea or to its ocean mouth. Oxley failed as the river lost its identity in swamps about 50km north of Balranald and the Murrumbidgee River.

At the beginning of June the following year Oxley led another expedition of 18 men and 19 horses northwards down the Macquarie River, starting from a depot at Wellington, north of Bathurst.

He had two boats and more than three tonnes of provisions (food, clothing and equipment), including about 1½ tonnes of flour. The heavy items were loaded into the boats and the remainder was carried by pack horses.

Oxley had his own horse but most of the others walked, as the horses were fully laden. The two parties travelled in sight of one another most of the time until they reached a point about 50km north of Warren where they found marshes.

Most of the party was sent back to a rocky hill that he named Mt Harris after his friend, Dr John Harris, who was accompanying him. Oxley and four others continued in a boat but were soon so deep into the Macquarie Marshes that the river was impossible to trace.

The second attempt to find an inland sea ended on July 7 when they returned to the others at Mt Harris.

From Mt Harris they could see the Warrumbungles 120km to the east. Oxley sent George Evans and a small party to reconnoitre. On his return Evans reported the discovery of a river which they named the Castlereagh.

Oxley decided to continue his explorations firstly to the Warrumbungles, then in a north-east direction. The boats were abandoned along with those non-essential provisions that the horses could not carry. Oxley buried a glass bottle at the summit of Mt Harris containing his plans and some silver coin but this has never been found.

On July 20  they set out. It was an arduous trek as it had rained heavily and the horses were constantly bogged all the way to the Castlereagh River and beyond. Oxley named various mountains in the Warrumbungles including Mt Exmouth. Commentators claim Oxley erred in his position of Mt Exmouth which is now identified 13km to the south. Actually, it is the modern geographer who mistakenly labelled it Mt Bulloway and put Mt Exmouth further south.

Continuing north-east, the party discovered the Pilliga, the Liverpool Plains and the Peel River before climbing The Great Dividing Range to Walcha. Oxley intended to reach the coast north of Smoky Cape but precipitous gorges prevented his descent with horses. He was forced southward and reached Mt Seaview (“Sea View Mount”), where he found a magnificent vista of the ocean and the Hastings River.

On October 8 the party arrived at the entrance to the Hastings and Oxley named the area Port Macquarie. (He returned in 1819 on Lady Nelson and surveyed the harbour and river up to Wauchope.)

Matthew Flinders had charted the NSW north coast in 1799 and 1802 but failed to see any rivers. Oxley used these charts expecting an easy passage to Port Stephens along the beaches and behind headlands. His first obstacle was the Camden Haven River at Laurieton. He thought it was a lagoon and tried to walk around but was forced back to the entrance.

They built a canoe to take their provisions across and swam the horses, however the horses were now in poor condition and one drowned.

On October 18 at Kylies Beach south of Diamond Head they noticed a boat on the beach filled with sand.

Oxley recognised it as a boat from the Jane, which had disappeared with a total loss of crew. The Jane itself was discovered some days later on the beach south of Old Bar.

Arriving at Harrington the following day they were confronted with the Manning River and no possibility of getting the horses across safely. Twelve men were sent back 20km to dig out the Jane’s 3.6m boat and return it to Harrington.

It needed caulking but was otherwise in good condition. Oars had to be made. Three days later they transferred all the provisions to the southern shore then towed the horses across. Continuing down the beach six miles in heavy rain they found another distributary of the Manning at Old Bar and had to fetch the boat to cross it.

This time they resolved to carry the boat all the way to Port Stephens, a total of 145km.

On October 25 they camped at Red Head and from nearby Black Head they could see Cape Hawke and the entrance to Wallis Lake.

On reaching Tuncurry on Monday, October 26 the boat was used again to cross the entrance to Forster. While doing so, William Blake was speared by an Aborigine from behind, the spear stopping at his breastbone. On turning to face his attacker, he received another spear to his abdomen. He was carried 70km to Port Stephens and survived.

They spent the night on Main Beach near the wreck of the Governor Hunter that had foundered a few months before.

Oxley found the next day hard going: “ We did not make much progress this day, being greatly embarrassed by the thick brushes which border on the coast in the vicinity of Cape Hawke, and fresh water swamps near the edge of the lake.”

They had covered only four miles compared with the usual 10 to 15. The actual camping place was probably at the lake on Lakes Estate or Dunns Creek. They cut a track to Janies Corner and climbed the hill to see the extent of Wallis Lake and the isthmus to Tiona.

On the October 28 they walked the length of Seven Mile Beach, climbed Booti Hill with their 400kg boat and 16 heavily-laden horses, and descended to Elizabeth Beach. It was a hot day and the injured Blake was not travelling well, so they camped by the stream at the southern end. Oxley climbed to the top of Charlotte Head, taking bearings of various landmarks to establish his position.

On October 29 they walked across the hills behind Blueys Head and joining the beach at Cellito. They camped at the southern end of Sandbar at Smiths Lake noting: “This neck of sand appears likely to be occasionally washed away, and to form a shallow opening into this portion of the lake.”

Another attack by natives involved a shower of spears at Big Gibber Headland between Sugarloaf Point and Port Stephens. Fortunately, no one was injured.

The expedition reached the north shore of Port Stephens on November 1, 1818. The following day Oxley sent George Evans and three others across Port Stephens in the boat where they continued on foot to Newcastle 48km away to get a ship to pick up the rest of the party. He arrived the same day and the party was picked up on the November 5 and returned to Sydney.

Twelve of Oxley’s men were convicts but in December 1818 Governor Macquarie pardoned all and extended land grants to them in appreciation of their efforts. William Blake survived. Malcolm Tompson