Hence I confined my comments to mineral engines. As for the rest, it's more complicated.   The Stockton & Darlington used mineral engines that were initially 4-coupled of the Locomotion/colliery type, then 6-coupled of the Hackworth twin-tender type in the 1820s-40s, with low dumb buffers matched to chaldrons; this was what I had in mind.  These stretch from the inception of the line right through to the last Tory and Miner class locos, finishing about 1847, and the Hackworth types
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