They were amazing, there's not much about them on the internet, although these images from Mike Hollingshead are similar to what I saw...
http://www.extremeinstability.com/08-8-29b.htmThe only difference was that there where more in Cookstown, all in a line with flickering/twisting motions, with bright white colours. The entire motion of the parent fog bank was like an upside-down waterfall. I will never look at fog the same way again. It would be worth going out before sunrise with the camera and watching for them. Which I might do.
Those dust devils sound great, I seen several brilliant examples during one hot Summer several years ago but none since. I will be more observant from now on. Cheers