In 1870 the river traffic had grown so much that bringing bunker coal from Calcutta was hampering traffic earnings. The Ledo coalfields were opened up and a short railway built between the coalfields and Dibrugarh on the Brahmaputra to carry the bunker coal. Soon other uses were found for coal. The tea factories changed over from wood fuel to coal for drying and curing tea leaves. The gardens were not all by the riverside and so railway had to be laid to haul coal for them. Eventually Assam was connected by railway with the port of Chittagong and Calcutta.
Tea and oil were its main exports. Coal was mined for local use and for Chittagong’s bunker stocks. The manufacture of tea chests had hidden taken up. The railway had its workshops and some engineering works catered to the gardens and the oil installations.