It is a while since I posted, but I have begun the process to transfer my forum post images from IMGUR to freeimagehost.
I was reading Steve Banks' website and he in the article he had a nice shot of a GCR 9F 0-6-0 hauling a coal train near Leicester around the time of the grouping.
There is no GCR 9F on the DLS but Camscott has an LNER J11 and we have PFlindley's GCR V15.
So, during the Big Four era, here is a former GCR 9F 0-6-0, now LNER J11 Class hauling a loaded C class coal train south on the Up line approaching Whetstone.
A further view, south of Whetstone showing the variety of wagons to be found in a coal train of the era. 3, 5, 7 and 8 plank types available in-game with company and private owner wagons, all wooden. Steel wagons would come in time, though, as Steve Banks said, it would take many years to sweep away all the wooden wagons from the system.
In Dennis Rowlands "Keeping the Balance" articles from the 1970s he made clear that the LMSR of the period just prior to WWII hauled many coal trains and most of the wagons in those trains were private owner types. This meant that coal trains could be very varied in composition. The GCR London Extension similarly appears to have operated coal trains with a wide variety of PO wagons. The NE Area of the LNER had a rather different environment, which was a legacy of the NER's preference for colliery owners to use NER Hopper wagons for transport of their output. However, even in the NE Area of the LNER there were private owner wagons to be seen at the pithead screens as NE colliery owners supplied coal by rail to regions outside the NE of England. They also filled wagons for stationmasters' landsale coal business at stations and some of that was in the colliery owners' own wagons.