Geology/geomorphology lesson (oversimplified):
The eastern US has, as its backbone, a mountain range called the Blue Ridge/Smokey Mountains/ and Appalachians (the easternmost part of the Appalachians from PA northeasteward). These are made up of preCambrian igneous and volcanic rocks. These oldest rocks have been around the entire time that the rocks from more recent ages were being deposited, so many of the more recent (Paleozoic) sedimentary rocks have their clay content derived from the basement preCambrian rocks. The Basement rocks are and were rich in heavy metals, in Iron, etc. A professor of mine one time gave a paper on iron in the Shady Dolomite soils and talked about the potential to strip mine the soils as a source of Fe in a possible emergency.
These soils that developed on the Paleozoics, that incorporate older clays have then been redeposited in the Triassic Basins on the east side of the Moutains, from CT, to Virginia, into NC, and a sliver in the buried one in GA. The Triassic Basins also have fresher clays and cobbles from the same basement rocks as the old Paleozoic soils.
And these have been the source of all the Mesozoic and Cenozoics on the Coastal Plain. Sometimes, the formations are sands, the clays were winnowed out and deposited farther out.
AND, because Europe and North America were joined when this was happening (remember the word Gondwana?), there are similar soils in Europe. England has the Old Red and New Red Sandstones, that so strongly resemble our Triassic Basins, but not the same age but the red clays around Chester England grow some magnificent roses (I asked many folks in Chester and all looked at me as if I were looney when I asked what fertilizers they used. They're on soils on or after the ?New Red SS.)

Our red soils have a lot of minerals and very little lime; they are old and the components that could have been leached out of them, have been leached out. This yields a really persistent red soil (the bane of anyone who does laundry for gardeners).

I don't know much about periglacial soils, but I've seen some gray and clammy soils to our north, where all soils were affected by the glaciers. And I don't know anything about the conditions of Greece. (I did find out that the famous monasteries were built on pillar shaped mountains made of conglomerates.)

This red clay holds water well. And what I've seen is that roses can do well here, just not roses on Dr. Huey rootstock which prefers a slightly basic soil.

The red clay in my yard is at least workable. Especially if it is moist and mixed in with some amendments.

The gray sticky clay is like playdough. It can't support plants from what I've seen. And not even the strongest clay buster can grow roots through it. I have streaks of it in my yard, which I've avoided planting in. I took the plunge this year and planted 9 roses on top of it. So far so good.

You are right about the laundry, Ann. I often have oranges stained feet and hands from the clay.

But I pretty sure I have mostly Dr. Huey root stock and it seems to be OK in the red clay. Maybe because I do amend when planting.

Ann,
That's a great exposition. I wish I had someone to give me a primer on our local geology.

I don't know whether all gray clay soil is equal. We have alkaline clay soil throughout, some of it tan-to-orange colored, with a broad belt of gray clay that's practically ceramic quality. Naturally we have much of our rose garden in the pottery clay. Very heavy amendment helps, and the Tea and China roses actually like it pretty well, amazingly. The Gallicas are also growing in it. We put down ten tons of hay this year, and I foresee using the same amounts for years to come. It's an article of faith with me that eventually this will make a difference.

Melissa

Our clay soil here in my part of California is a yellowy-tan color. I wish I knew more about its history and composition. Actually, I'm planning to sign up for a class at the local community college on soil; if I get in, perhaps I'll get the answers to my questions.

Ann, thanks for the explanation about red clay, and Marianne, thanks for posing an interesting question!

Rosefolly

Thank you Ann for the great lesson! It made me more interested in my own soil, too. I am embarrassed that I haven't even tested it for Ph. I know it is rich in nutrients but it will never become black and crumbly like some soils in the south of Sweden. I shall have to add compost to it forever to make it workable, especially for growing vegetables. Roses seem to do okay if the planting hole is well prepared.

Ann, you reminded me of that old (1970s?) commercial for Oxydol detergent, with the lady from somewhere deep South, who said how good it was for the red clay and mud "rayedddd clayyyyyyyyyy and Muhdddddd." It was great fun to hear her say it. I don't know that oxydol even exists anymore.