In 1857, four years after his appointment to the last mentioned office, he was offered the post of managing agent of the Boston & Lowell road and its branches, in connection with the Nashua & Lowell line. The magnitude of the operations of these two roads, with their auxiliary lines, was very great, and in their management required executive ability of the first order. The responsibilities of the position were onerous, and involved the appointment of superintendents, subordinate officers, and foremen, determining a code of regulations for their guidance, the adjustment of time-tables, tariff-rates, and fares, the purchase of supplies, and many other cares incident to the working of a complex and extended carrying-trade. The manner in which these duties were discharged was attested by the smooth working of the organization in its details, and the satisfactory results to the stockholders. In this period of service, which included about eighteen years, the great depot on Causeway street, Boston, was erected under the general management and supervision of Gen. Stark. In its first inception, this magnificent building, with its approaches, was intended to furnish terminal facilities for two or more roads. A contract to that effect was completed with the Massachusetts Central road. Negotiations were also entered into with the Eastern Railroad Company for a joint occupancy of the building, and a proposal was obtained from that company to pay fifty thousand dollars annual rental, besides bearing a proportionate share of the running expenses. Stark submitted this proposal to his associates, recommending its acceptance; but it was declined, on the ground of inadequate compensation, the president of the Boston & Lowell and Nashua & Lowell roads saying, in his written reply to Stark:-- "While the income is certainly important to us, we have built the station for our own accommodation, with our eyes open, and I think our directors won't flinch from our position and divide with them, unless they pay well for it." The unsuccessful termination of this negotiation, and the want of accord in other matters of general policy between Stark and some of the then prominent directors of his roads, embarrassed him in his duties, and he resigned the position of general manager in March, 1875, but retained his seat in the board of directors until the following year. During his business connection with the combined roads of the Merrimack lower valley, the influence of Gen. Stark in developing great public business interests is recognized by all familiar with the subject. The far-reaching and comprehensive plans for a direct through line connecting Boston with the West, realized in 1863 by connection of the lines of the Merrimack valley, Vermont Central, Ogdensburg, and other roads, were the direct result of Stark's labors and influence; and he was manager, for several years, of the line from Boston to Ogdensburg.