Monson Slate Company had been purchasing Monson Railroad stock for several years, and gained control of the railroad in 1908. Conductor Harold Morrill, who had started working for the railroad as fireman in 1884, was promoted to superintendent; but he continued to act as conductor through 1938. Track was extended with of 35-pound () rail to Eighteen Quarry and Forest Quarry on Monson Pond in the summer and autumn 1909. The Monson combination car carried 11,466 paying passengers in 1912, but superintendent Morrill observed that an automobile garaged in Monson was offering public conveyance and taking approximately 25 paying fares per week from the railroad. Both of the old Hinkley locomotives had serious boiler leaks, cracked cylinders, and/or broken frames since 1905; but they soldiered along until a new Vulcan locomotive arrived on 20 February 1913. In 1916 Monson's location provided an opportunity to purchase the longest freight cars operated by the railroad. The
Sandy River Railroad shop at
Phillips, Maine was rebuilding 185 older gauge logging railroad flat cars into what became a fleet of 158 -long flat cars of the
Sandy River and Rangeley Lakes Railroad being purchased by the
Maine Central Railroad in 1912. The Maine Central simultaneously contracted with Boyd and Harvey Lumber Company to cut
railroad ties in the western
Penobscot River drainage of the roadless
Maine North Woods. The lumber company built the gauge Carry Pond and Carry Brook Railroad in 1914 over the northwest carry from the eastern end of Seboomook Lake to Northwest Cove at the northern end of
Moosehead Lake. Draft animals pulled two 28-foot-long flat cars over the railroad to deliver the ties to Moosehead Lake where they were floated across the lake for loading at Kineo Station on the northern end of the Maine Central Railroad
Kineo Branch. After the ties had been delivered, the lumber company sold the two flat cars to the closest gauge railroad at Monson. The Monson Railroad purchased a couple of hand car trailers which could carry broken slate scraps from the quarries for use as ballast along the line. Within a few years, the Monson railroad became the only railroad in Maine with a completely rock-ballasted main line. The railroad kept the link-and-pin couplers for another quarter century of operations; but the oil headlights were removed when damaged by derailments. The locomotives thereafter ran without any headlights. Monson briefly considered a
Davenport Locomotive Works 2-6-2 (similar to those being built for
United States Army trench railways) before purchasing another Vulcan in 1918. Hinkley locomotive #1 was retired when the second Vulcan locomotive was delivered. Elimination of need for a source of spare Hinkley parts encouraged the innovative shop crew to strip old Hinkley #2 of all exterior fittings and attach a snowplow blade. Although the new snowplow was less likely to ride up on snow drifts, it was more likely to derail; so the old wedge plow remained in service. ==Decline of Service==