How come a structural dome has the oldest rock in the middle and a structural basin has youngest rock in the middle? they both look the same to me. How can you tell them a part?

-- Andrea Gibbs (agibbs@oswego.edu), December 05, 2002

Answers

Think of the law of superposition - ie - younger layers of rock on top of older ones. When an area of strata is uplifted, and erosion occurs (like in a dome), the younger layers will be carried away from the highest point and the older layers will be exposed. Same goes for a basin, only in the middle less erosion occurs. Also, in a basin new sedimentary rock can be forming. Say the basin was at one time a lake, younger rocks will be formed in the middle.

-- Nicholas Bishop (nfbishop@engmail.uwaterloo.ca), December 07, 2002.