The famous Foothills Erratic Train in Canada is the most famous example of a "train" or trail of erratics -- as distinct from an erratic "fan" where boulders from one source are spread widely across an arc of countryside. Both types are well documented -- but it should be borne in mind that a fan is nothing more than a collection of erratic trains which are quite close together, arising from changes in ice directions during the course of a glacial episode. There is no mechanism for erratics to "spread sideways" in a glacier of ice sheet -- they have to move in the direction of ice movement, up or down, but always forward and never laterally.
The interesting thing about the Foothills erratic Train, as pointed out by Lionel Jackson and many others, is that the string of erratics was created by the parallel streaming of two very large ice masses -- the Cordilleran Ice Sheet to the west, and the Laurentide Ice Sheet to the east. With very good reason, Lionel and I proposed that this was a close parallel to the situation than occurred in the Bristol Channel area at the peak of the (Anglian?) glacial episode: