I have been following the calcite "sand" posts with interest. George, I suspect the soils may be more important than you acknowledge. I think it depends more on residence time and partial pressure (and, of course, plant activity) than "thickness" of the soils as such.
In a related item, I have the PDF of the USGS Wind Cave water report. I can send it if anyone wishes. Now we just need to find the Old Lace to go with all the arsenic. DirtDoc
