Why the pond leaks, or the Ohio Alps
Sign resting on cut sandstone from the old log cabin
My uncle, Dr. Gordon Grender, is a Professor Emeritus of Geology at Virginia Tech. Sometime during the 70′s, he took a sample of the sandstone that is ubiquitous at the Hollow, had a slide prepared, and provided us with this report on its composition and characteristics:
Here’s specimen HEIHOL, which we picked up on our walk down near the creek last summer. This is the stuff that litters the hillside across from the trailer and makes the pond leak. It’s pretty dull stuff except to a dyed-in-the-wool quartz-lover.
Medium-grained quartzite with rare accessory minerals, loosely cemented by quartz and hematite. Extreme porosity of about 40%; excess porosity probably once occupied by calcite, long since leached away [note: the neighbor's spring goes cloudy white after a heavy rain]. This particular specimen has probably been on its way to the creek for at least 20,000 years; perhaps more. Long enough to remove all of the calcite, anyway. Originally it accumulated on a gentle, stable beach about 200,000,000 years ago (give or take a few million), before the collision of Africa and Eurasia with North America, which raised a Himalayan-scale mountain range about 250 to 350 miles Southeast of the Hollow–if you’d been there you might have been able to see it’s snow-capped peaks on a clear day. After that, no more quiet beaches! These rocks were buried a few thousand feet deep by other rocks; they “floated” upward as the overlying mass was removed by erosion–a process that continues unabated, but which will slow and stop sometime in the next 50 to 100 million years as the region comes into equilibrium–unless something else happens to disturb it.
- Thin section of Heiser Hollow Sandstone
Sandwich the thin-section between the polarizers. The salt-and-pepper texture is QUARTZ. How dull. Many other minerals are so colorful in polarized light! Gravestones and foundation stones made out of this rock go to pieces quickly –its that calcite cement, which is soluble in rainwater over a few decades.
November 26th, 2011 at 11:30 am
[...] reasons, not the least of which is the cost of both material and application. As discussed in an earlier blog entry, My Uncle Gordon determined that the pervasive local sandstone (commercially quarried close enough [...]