The disappointment was undoubtedly great at not finding even a large river flowing into the gulf. The hope of a strait had been abandoned as the continually converging shores, shallow waters, and diminishing banks made it clear, long before the head was reached, that the theory of a bifurcated Terra Australis was impossible. But as Flinders completed his chart and placed it against the outline of the continent, he might fairly enjoy the happiness of having settled an important problem and of taking one more stride towards completing the map of the world.
The Investigator travelled down by the eastern shore, once hanging upon a near bank for half an hour, and by March 20th was well outside. The length of the gulf, from the head to Gambier Island, Flinders calculated to be 185 miles, and its width at the mouth, in a line from Cape Catastrophe, 48 miles. At the top it tapered almost to a point. The whole of it was personally surveyed and charted by Flinders, who was able to write that for the general exactness of his drawing he could "answer with tolerable confidence, having seen all that is laid down, and, as usual, taken every angle which enters into the construction."
The next discovery of importance was that of Kangaroo Island, separated from the foot-like southern projection of Yorke's Peninsula by Investigator Strait. The island was named on account of the quantity of kangaroos seen and shot upon it; for a supply of fresh meat was very welcome after four months of salt pork. Thirty-one fell to the guns of the Investigator's men. Half a hundredweight of heads, forequarters and tails were stewed down for soup, and as much kangaroo steak was available for officers and men as they could consume "by day and night." It was declared to be a "delightful regale."
The place where Flinders is believed to have first landed on Kangaroo Island is now marked by a tall cairn, which was spontaneously built by the inhabitants, the school children assisting, in 1906. An inscription on a faced stone commemorates the event. The white pyramid can be seen from vessels using Backstairs Passage.* (* See the account of the making of the cairn, by C.E. Owen Smythe, I.S.O., who initiated and superintended the work, South Australian Geographical Society's Proceedings 1906 page 58.)
A very short stay was made at Kangaroo Island on this first call. On March 24th Investigator Strait was crossed, and the examination of the mainland was resumed. The ship was steered north-west, and, the coast being reached, no land was visible to the eastward. The conclusion was drawn that another gulf ran inland, and the surmise proved to be correct. The new discovery, named St. Vincent's Gulf, was penetrated on the 27th, and was first explored on the eastern shore, not on the western as had been the case with Spencer's Gulf. Mount Lofty was sighted at dawn on Sunday, March 28th. The nearest part of the coast was three leagues distant at the time, "mostly low, and composed of sand and rock, with a few small trees scattered over it; but at a few miles inland, where the back mountains rise, the country was well clothed with forest timber, and had a fertile appearance. The fires bespoke this to be a part of the continent." The coast to the northward was seen to be very low, and the soundings were fast decreasing. From noon to six o'clock the Investigator ran north thirty miles, skirting a sandy shore, and at length dropped anchor in five fathoms.
On the following morning land was seen to the westward, as well as eastward, and there was "a hummocky mountain, capped with clouds, apparently near the head of the inlet." Wind failing, very little progress was made till noon, and at sunset the shores appeared to be closing round. The absence of tide gave no prospect of finding a river at the head of the gulf. Early on the morning of the 30th Flinders went out in a boat, accompanied by Robert Brown, and rowed up to the mud-flats at the head of the gulf. Picking out a narrow channel, it was found possible to get within half a mile of dry land. Then, leaving the boat, Flinders and Brown walked along a bank of mud and sand to the shore, to examine the country. Flinders ascended one of the foot-hills of the range that forms the backbone of Yorke's Peninsula, stretching north and south upwards of two hundred miles.
At dawn on March 31st the Investigator was got under way to proceed down the eastern side of Yorke's Peninsula. The wind was contrary, and the work could be done only "partially," though, of course, sufficiently well to complete the chart. The peninsula was described as "singular in form, having some resemblance to a very ill-shaped leg and foot." Its length from Cape Spencer to the northern junction with the mainland was calculated to be 105 miles. On April 1st Flinders was able to write that the exploration of St. Vincent's Gulf was finished.
FLINDERS'S CHART OF SPENCER'S GULF, ST. VINCENT'S GULF, AND ENCOUNTER BAY