I enjoyed this thread immensely.
I could not possibly dignify this subject more than you have already done, but it is good to know that others care as much about the history of our region and its people as you do. My family has been in the South going on nearly 400 years now and I have enjoyed learning about all the facets of both our own people and the people of the South in general.
As to the stacked-stone graves, or crypts, I cannot speak only to say that I have never heard of such a thing in my neck of the woods (SC). There were, as another poster said, large amounts of Welsh folks living in what became iron country in the last half of the 1800s and it would not surprise me to learn that the phenomenon was originated or influenced by them for some reason.
Let me not then die ingloriously and without a struggle, but let me first do some great thing that shall be told among men hereafter. ~Homer