Sir Thomas Mitchell - Warrawalong and Wollombi

On page 9 of his Three Journeys Into the Interior of Eastern Australia, Mitchell also gives a description of Mount Warrawalong, where he surveyed part of the route for the Great North Road:- "... These isolated heights generally consist of trap rock (volcanic rock) and are covered with rich soil and very heavy timber. The most remarkable is Warrawalong-whose top I first observed from the hill of Jellore in the south, at a distance of 108 miles. This being a most important station for the general survey which I made previously to opening the northern road, it was desirable to clear the summit, at least partly, of trees, which work, after considerable labour, was accomplished- the trees having been very large. On removing the primeval forest, I found the view from that summit extended over a wild waste of rocky precipitous ravines, which debarred all access or passage in any direction, until I could patiently trace out the ridges between them, and for this purpose I ascended that hill on ten successive days, the whole of which time I devoted to the examination of the various outlines and their connections, by means of the theodolite."

The Mirage and the Theodolite

It is worth considering another aspect of Thomas Mitchell's work in New South Wales, using the content of a paper by Martin Thomas, Limited Legibility: Sir Thomas Mitchell and the Great North Road, in the Forum Papers presented at the conference on Exploring the Great North Road in 1998.

As one of its most senior officers since 1828 as Surveyor-General, Mitchell had made lengthy expeditions out into New South Wales, west from Sydney. In all of his travels, there was a ceaseless extension of his trigonometrical survey, setting new standards in scientific travel. He was skilled in drawing and mapping, practising as both an artist and a scientist. He had experienced the optical illusion (known to us as a mirage) produced by rising hot air and moisture to make akin to a great lens in the lower atmosphere - a refractive effect.

Mitchell's astonishment had been his reaction when he was surveying for the Great North Road and on the ranges adjoining Mount Warrawalong encountered the illusion. There, on the western horizon, he noticed "Several gigantic ranges ... overhanging with trees & glistening with rocks." Staring at his notebook in stupefaction-previously he had sketched the view-Mitchell reached for his telescope, enlarged the enlargement, and watched the mountains "change shape" until one "fell away in the middle". (Mitchell; Field, note and sketchbook 1828-1830 MS Mitchell Library [C42]) This first encounter would set the tone of his dealings with optical illusions. On the River Darling, six years later, he not only observed the vision through his telescope, but took readings with a theodolite, obtaining bearings on the refracted ranges that appeared before him "from a spot whence it could be but seldom visible," and thus incorporating the "mirage" into his trigonometrical survey. (Mitchell, Three Expeditions Vol.1, p239)

The Country around Wollombi

On page 11, Mitchell gives a picture of the country around Wollombi with a mention of the settlers who had moved into this area:- "It was quite dark on the evening of the 26th before I reached the inn near the head of the little valley of the Wollombi, a tributary stream to the river Hunter. ...In the ... Upper Wollombi we find but little breadth of alluvial soil but the water never fails, and this has already attracted settlers to its banks - and those small farmers who live on a field or two of maize and potatoes and who are the only beginning of an agricultural population as yet apparent in New South Wales - shew a disposition to nestle in any available corner there."