Regarding that Longdyke tramway; it does a sharp turn to due North just south of the Cawledge burn valley (or valley of a tributary feeding in to it). At that point on the track is another large building, I assume a second hauler and they must have changed the tub sets over there??
you can see most of the track-way from longdyke to Alnwick here: the sharp turn is where the green arrow is:
http://maps.google.co.uk/maps?q=55.3...gl=uk&t=h&z=15
Interesting to see if any remnants of the bridge survive in that area.