The Monson Railroad was a narrow gauge railway, which operated between Monson Junction on the Bangor and Aroostook Railroad and Monson, Maine. The primary purpose of this railroad was to serve several slate mines and finishing houses in Monson. According to the Scientific American of 17 May 1890, it was the smallest railroad in the United States. Equipment was never modernized, and the railroad used antique stub switches and link-and-pin couplers to the end of operations in 1943. The line was the last commercial carrier in the United States to use such couplers or to run above ground on a gauge. (The gauge Chicago Tunnel Company continued underground operation as a common carrier freight subway until 1959.) Construction The slate underlying what became the town of Monson, Maine had very low ionizable mineral content, and was well suited for manufacture of electric switchboards. Quarrying commenced in the 1860s and slate finishing operations began in 1870. Slate was shaped into sinks, bathtubs, tabletops, chalkboards, roof shingles, and headstones. Transporting these heavy slate products was difficult in any weather, and became nearly impossible when spring thaw turned the roads to slush and mud. The Monson and Athens Railroad Company was chartered 1 November 1882, when the standard gauge Bangor and Piscatquis Railroad (later part of the Bangor and Aroostook Railroad) bypassed Monson by six miles. The railroad was built with 30-pound () rail in the summer of 1883, reached Monson on 4 September, and opened for business on 22 October. Initial equipment consisted of two wood-burning locomotives from Hinkley Locomotive Works and two box cars, fourteen flat cars, and a combination from Laconia Car Company. The main line was promptly extended down a five percent grade to the Monson Slate Company approximately beyond the Monson village depot. A car shed for the combination and a two-stall engine house were built near the depot with a passing siding and a turntable. The turntables were a bit small for the locomotives, although they proved useful when a wedge snowplow arrived a few years later. Monson train crews found it much more convenient to run the locomotive in reverse for six miles than to wrestle it around on the turntables. Early Common Carrier Operations Four daily round trips were scheduled to meet each of the standard gauge trains. The Monson train crew consisted of an engineer, a conductor, and a fireman who doubled as brakeman.