side view definitely looks siliceous, lay terms we would call it mudstone, but I don't even know if I would call it that with that side view definitely looking like chert. if you spit on it does it soak it up?
I forget how it works exactly been out of college a while but I think you get that kind of formation when you have a sand and mud boundary and you apply pressure and the mud needs somewhere to go so it moves around whats applying pressure and forms kinds of blobs and valleys. sorry if I'm butchering the explanation to those who know what I'm trying to say but that's the best I can remember it.