The Tower of London

1. The White Tower is built mainly of Caen Stone and Kentish Ragstone and was originally whitewashed.
2. The Crown Jewels contain the oldest stones in the Tower; the diamonds were formed three billion years ago.
3. St Thomas's Tower and Traitor's Gate: restored with interlocking blocks of Kentish ragstone above the original Caen Stone arch.
4. Beauchamp Tower: inside, the Caen Stone walls have been carved by desperate prisoners captured by the Tudors.
5. Bloody Tower: the left-hand gate shows honey-coloured and cross- bedded oolitic limestone.
6. Middle and Byward Towers: massive, pale buff Caen Stone at the base, with upper levels of white Portland Stone.

Learn more about The Tower of London's building stones in the Holiday Geology Guide available from the BGS Bookshop.

• Tower of London Holiday Geology Guide in the BGS Bookshop
• GeoBritain map