JOINT:
Joints are fractures that often form in rocks in response to tension (stretching) stress. The sedimentary rock layers shown on the right contain two perpendicular sets of joints, and these joint sets cause the outcrop to appear angular and blocky.
	Joints tend to form more readily in strock rock (like deformation bands) than in weaker rock (like the surrounding porous sandstone).  The key to their significance in this project is that joints are cracks, or openings, that can allow fluids to flow across otherwise impermeable deformation bands.