edge writes:
I mentioned the apparently equal weathering above and below the unconformity as evidence that the standard interpretation is false: i.e., that the lower section was laid down and then tilted, and that a long time later the upper section was deposited on top of it. Since millions of years are usually ascribed to such blocks of strata, there should be a difference in weathering apparent between the two blocks, but they show no such difference.
No. I said that the weathered rock was removed by mechanical erosion and that the lower rocks were covered shortly after erosion.
I didn't understand this, but let me venture a guess: do you mean that the lower rocks were eroded a long, long time ago, then shortly after that erosion the upper layers were deposited upon them, then the upper layers were buried, then they were exposed along with the lower layers that now make up a small cliff face, then weathering removed some upper layer rock by mechanical erosion. If that's not it would appreciate some clarification.
In fact, in the images of the unconformity there is no tectonic structure.
Not sure which images are meant.
There were pretty obvious fractures in the granite showing spheroidal weathering that would only occur during long periods of weathering. The purpose of this image was to show Faith a location where the underlying rocks actually were more weathered than the rocks overlying an unconformity. This is due to the fact that the granite was not being mechanically removed as it was weathered. I can see that my attempt to help the understanding of unconformities failed.
I might not get this, either, but anyway, here's the image:
My guess is that you're trying to explain that the weathering effects that caused the way the overlying sandstone and the underlying granite appear today was not what caused the embedded granite boulders to become mechanically weathered into spheroidal shapes.
Also, about this part:
But it was interesting for the fact that a depression in the granite was not filled by sand from the sandstone layers above, which to my mind shows that the depression occurred after the sandstone was in place.
An artifact of an oblique image.
About the depression Faith refers to that's about 1/3 of the way from the left side of the image and at the boundary between the sandstone and granite? That looks like it's really there to me. It looks like one of the granite boulders detached from the granite face and fell to the ground.
Faith's comment also highlights again her belief that holes and depressions in rock faces represent real cavities buried in the strata that have been revealed by erosion, rather than that they're just caused by pieces of rock breaking off and falling to the ground.
--Percy