An article was written for the New York Times by a very distinguished and reliable observer at a Solar Eclipse in America at the turn of the last century. The text is very descriptive, and can be found here. The main point of interest for me is the extract below, which clearly describes how some of the wave forms of the Shadow Bands are moving at right angles to others. I suspect the Shadow bands are more than mere "curiosities".

Their direction and velocity at the beginning of totality and at its close, as well as the interval between the bands, was not the same at both times; and it is curious that observations obtained at the comparatively short distance of two or three hundred yards, but across a slight intervening ridge, showed a deflection almost at right angles to that obtained by the members of our party.