A joint's height refers to its dimension generally in the vertical direction for horizontal strata. Since most joints within layered sedimentary rocks are oriented perpendicularly to the layering and joints commonly terminate at layer boundaries, joint heights in layered rocks are controlled primarily by the thickness of the jointed units, which are generally brittle layers or amalgamated brittle layers in a sequence. Jointed units may be composed of one or many mechanically similar layers. However, joint heights in nature rarely exceed a few tens of meters. See also 'Joint Spacing - Layer Thickness Scaling' and 'Termination of Joints.' For massive rocks such as intrusive rocks this is not a factor. Keep in mind that joint zones or clusters, which commonly have a small amount of shear across them, are linked through many horizons.