![Top curves](../../../../jsp/jahia/templates/GSL/gsl_templates/img/keystage3/main_top_grad.gif)
Basalt sill, Northumberland
![Basalt hand specimen](../../../../webdav/site/GSL/shared/images/education_and_careers/RockCycle/RocksAroundBritain/Basalt%20resized.jpg)
The cliff is very steep due to the near-vertical joints in the basalt. The diagram is a cross-section through the sill, showing how the rock breaks along joints to form the steep cliffs on which the wall is built.
Hadrian's wall, Northumberland
![Hadrian's wall](../../../../webdav/site/GSL/shared/images/education_and_careers/RockCycle/RocksAroundBritain/HadriansWall%20xtrawide.jpg)
![Whin sill diagram](../../../../webdav/site/GSL/shared/images/education_and_careers/RockCycle/RocksAroundBritain/WhinDiag%20v2xtrawide.jpg)
![Bottom curves](../../../../jsp/jahia/templates/GSL/gsl_templates/img/keystage3/bottom_curve.gif)