[EarthResearcher333]

See Post 2,579 link below: I estimate the Amphibolite layer/section to be just under 2ft in length. What was more striking to me was that since coring was vertical, the Amphibolite section in the "middle", was sandwiched on each end with differing rock; - infers a laminar "seam". Not exactly a simplistic geological strata layering for structural engineering. Note the fractures in the core sample, including the Amphibolite section.

Core Sample Analysis - A hard Amphibolite rock seam (blue grey color) observable in the middle of the longer core sample being inspected.

[Rebelbase]

Thank-you!

[Repeal The 17th]

When the grey rock has all of those fractures and veins
that run through it and underneath it, I don’t see how the
grey rock is very much more resistant to erosion than the
brown rock. It is still going to crumble away.
It is not a homogeneous layer of rock.

Similar to the concrete slabs on the spillway,
they did not “erode” away from the top side,
they washed out from the bottom side and fractured and crumbled away.
(IANAG - I am not a geologist)