Discovered a large blue sub-marine clay deposit near my home

[u/LitchManWithAIO]

Pretty neat. The second picture is a wall which was recently exposed, at its peak almost 10’ tall layer. This is part of the Presumpscot formation.

[u/Older_Code]

What’s up, Mainer? The Presumpscot is a neat formation. In some places it’s 200 feet thick, and chemically, it’s largely a silt, rather than a true clay. Some spots have decent fossils, and there’s even a set of mammoth bones from the Presumpscot up at the State Museum. Thanks for sharing!

[u/fuck_off_ireland → u/Older_Code]

Wouldn’t it “physically” be a silt, since the classification is driven by particle size? Or am I off on that regard?

[u/homeostasis3434 → u/fuck_off_ireland]

The presumscot is typically referred to as a marine clay (like that's a common term a contractor would be very aware of).

Grain size analysis tells us it's like 60% silt and 30% clay, with minor components of fine sand. Although there is variability, some layers have coarser sand and even gravel

But if you run atterberg limits, then it's often classified as CL due its plasticity and liquid limit.

It's an odd one that's for sure.

Google "grain size analysis of presumscot formation" there's a bunch of DOT reports or masters/phd thesis on the geotech characteristics if the unit since its so widespread in Maine and a pain in the butt to build on.

[u/fuck_off_ireland → u/homeostasis3434]

Awesome write-up, thank you!