On August 10, 1849, he records: "I have been thinking for the last few days about fixing on some subject or pursuit on which to devote my life, as it is of no use first starting one subject and then another, thus learning nothing. After giving it a good deal of consideration, I have determined on studying 'Natural History,' not confining myself to any one branch of that vast subject. As this is a subject on which I intend to devote my leisure hours during the greater part if not the whole of my lifetime, I consider it to be of the greatest importance that I should lay a good foundation for it. I therefore intend during the ensuing winter to study the English language and composition, so as to be able to describe objects and explain my sentiments with greater clearness and precision than I can at present." The last sentence illustrates the systematic thoroughness of all his work which was one reason of his success.

Belt's "leisure hours" were soon more numerous than he had anticipated when recording his determination to devote them to natural history. Already his health had shown signs of giving way, and presently there was a nervous break-down which necessitated his giving up all work and being out in the open air as much as possible. But what appeared to be probably the wrecking of his life provided the opportunity which might not otherwise have occurred of encouraging and developing his inborn love of nature. Becoming a member of the Tyneside Naturalists' Field Club, he interested himself greatly in the local fauna and flora, and formed very complete collections of the plants, insects, and shells. His name occurs frequently in the "Transactions" of the Club as the recorder of species new to the district. His health gradually improved, but it was doubtful whether he would be able to bear the strain of any indoor occupation, for which indeed he felt an ever-increasing aversion.

It was the time of the discovery of gold in Australia, and after much discussion he and his elder brother joined the stream of adventurers and sailed in 1852 for Victoria. In this rough "school of mines" he acquired that insight into the building-up of the earth's crust and that practical knowledge of minerals which served him so well in after-life as a mining engineer. But although the whole colony was in the grip of the gold-fever, Belt retained the same quiet habits of observation which had marked him at home--for there, as to whatever part of the world his work subsequently called him, the engineer was always at heart a naturalist. He proved an excellent observer, and a certain speculative tendency led him to group his observations so as to bring out their full theoretical bearing.