The bed rock of the Peak District was formed 300 million years ago, close to the equator where the Carribbean is now. Imagine the clear water of a shallow warm sea, teeming with starfish and shellfish like creatures. In vast numbers and over 20 millions years, the remains of these creatures and microorganisms settled on the sea bed and slowly hardened to become the thick bed of limestone. The bed of limestone was shifted by the deep movements of the earth to where it is now.
The tors are sandstone, created as the sea and rivers met at a delta and deposited sand and mud, on top of the limestone. This rock was used to make millstones.