We have seen that, on his return from Edinburg College at the end of 1821, he had assisted in superintending the works of the Hetton Railway until its opening in 1822, after which he proceeded to Liverpool to take part with Mr. James in surveying the proposed railway there. In the following year we found him assisting his father in the working survey of the Stockton and Darlington Railway; and when the Locomotive Engine Works were started in Forth Street, Newcastle, he took an active part in that concern. "The factory," he says, "was in active operation in 1824; I left England for Colombia in June of that year, having finished drawing the designs of the Brusselton stationary engines for the Stockton and Darlington Railway before I left."[65] Speculation was very rife at the time, and among the most promising adventures were the companies organized for the purpose of working the gold and silver mines of South America. Great difficulty was experienced in finding mining engineers capable of carrying out those projects, and young men of even the most moderate experience were eagerly sought after. The Colombian Mining Association of London offered an engagement to young Stephenson to go out to Mariquita and take charge of the engineering operations of that company. Robert was himself desirous of accepting it, but his father said it would first be necessary to ascertain whether the proposed change would be for his good. His health had been very delicate for some time, partly occasioned by his rapid growth, but principally because of his close application to work and study. Father and son proceeded together to call upon Dr. Headlam, the eminent physician of Newcastle, to consult him on the subject. During the examination which ensued, Robert afterward used to say that he felt as if he were upon trial for life or death. To his great relief, the doctor pronounced that a temporary residence in a warm climate was the very thing likely to be most beneficial to him. The appointment was accordingly accepted, and, before many weeks had passed, Robert Stephenson had set sail for South America. After a tolerably prosperous voyage he landed at La Guayra, on the north coast of Venezuela, on the 23d of July, from thence proceeding to Caraccas, the capital of the district, about fifteen miles inland. There he remained for two months, unable to proceed in consequence of the wretched state of the roads in the interior. He contrived, however, to make occasional excursions in the neighborhood with an eye to the mining business on which he had come. About the beginning of October he set out for Bogotá, the capital of Colombia or New Granada. The distance was about twelve hundred miles, through a very difficult region, and it was performed entirely upon mule-back, after the fashion of the country.