These two sets of joints are called J1 and J2, and each has unique characteristics. Joints in the J1 set
run east-northeast throughout the Marcellus Shale. The J2 joint set runs generally north-northwest and
cuts across the J1 joint set. The J1 joint set happens to coincide with the modern underground stresses
found throughout the Northeast. Joints in the J1 joint set are spaced more closely together than those in
the J2 joint set. Joints in the J2 set are more likely to have been healed, which means the joint has been filled
in with minerals and is no longer a pathway for gas flow. These healed joints are still relatively weak because
the mineral cement gluing them together is weaker than the original bedding planes of the rock, and are therefore places where new fractures could grow