Gradual cooling of the earth

I have no idea where you can be getting your information from.Horizontal layers are formed in sedimentary rocks because sediments are laid down in horizontal rather than vertical beds. The cooling of the earth has nothing to do with it. It's hard to say anything about your rock just from looking at a picture, but I'm going to take a wild guess and say that it's metamorphic and that the layers seen on the side of the rock are not bedding planes but slatey foliation (see the article on metamorphic rocks in my Introduction To Geology Thread) ... in which case (a) those layers were not present when the wrong was formed and (b) you're holding it on its side. However, I could be completely wrong, and would defer to anyone who knows more about it than I do.

I think I see what's muddling you. You are being confused by vague memories of the process known as differentiation, which resulted in the sorting of the Earth into core, mantle, and crust. This is indeed a sorting by weight (or, to be precise, density), and it would indeed not have happened if the Earth had cooled to a non-molten state in a snap of the fingers.But this has nothing at all to do with the beds of sediment found in the upper crust.Edited by Dr Adequate, : No reason given.