On the 16th of April, 1858, he left the Geraldine mine with a lightly-equipped party of six, including J.B. Roe, son of the Surveyor-General. They had with them six pack and six riding-horses, and rations for 60 days. They proceeded up the Murchison, and on the 25th of the same month they reached a tributary called the Impey, which had been the highest point reached by Gregory the preceding year. This time, however, the party did not find such ample pasture as he had described. Still following the river up until the 30th April, on that day they struck off on a nor-north-east course, the course of the Murchison tending too much in an easterly direction to lead them speedily on to the Gascoyne. On the 3rd they reached a gentle stony ascent, which proved to be the watershed between the two rivers. Descending the slope to the northward, they soon came to the head of a watercourse flowing northwards. They followed the new creek, and on the 6th of May came to a river joining it from the eastward, which at last proved to be the Gascoyne. Gregory kept down the south bank of the Gascoyne, and on the 12th of May passed a large tributary coming from the north, which he named the Lyons. On the 17th they ascended a sandy ridge about sixty feet in height, and had a view of Shark's Bay. He returned along the north bank of the river, and having reached the Lyons, followed that river up. On the 3rd of June he ascended the highest mountain yet discovered in Western Australia, which he named Mount Augustus, after his brother. Gregory gives the elevation at 3,480 feet, but Mount Bruce in the Hammersley Range, to the north of it, has since been found to be higher.* From the summit, however, he had an extensive view, and was enabled to sketch in the courses of the various rivers for over twenty miles. *[Footnote.] 3,800 feet. As they had now been out 51 days, and their supply of provisions was approaching the end, the party turned back at Mount Augustus, and struck southwards. On the 8th the Gascoyne was re-crossed at a place where its course lay through flats and ana-branches. On the 10th of June they again came to the Murchison, and followed it down to the Geraldine mine, and finally reached Perth on the 10th of July. This expedition, so fruitful in its results to the pastoral welfare of the colony, cost the settlers only their contributions in horses and rations, and a cash expenditure of forty pounds.