prize9-7, Exercise 1: Order of the rocks

Model answer (check the details):

Oldest: the sandstone. It is cut by the dyke, so it must already have existed.
Middle: the granite dyke. By cross-cutting, it is younger than the sandstone it cuts.
Youngest: the limestone, which lies flat across both. By superposition, a layer lying on top of the others was deposited later, and because it is not cut by the dyke, the dyke came first.

There is an unconformity between the granite and limestone if the surface of the older rocks was eroded before the limestone was laid down.

Care: confirm that the limestone is not cut by the dyke, since that is the evidence for the order.