not all cracks have slippage or movement at all. Joints and cleavage are teeny cracks that dont show any appreciable movement. They are like tension cracks in modelling clay, ares elf healing but do provide paths of preferred "bustage". Joints that are most famous are the columnar ones of The Devils Tower or sheet joints in sandstones and limestones.When these joints are present in large amounts they impart a preffered crack structure onto rocks that everyone calls "cleavage" .All these are helpful in determining which way forces have acted and which way fluids would have moved .
Yeh the MArcellus is present past the Appalachian front and is present from near surface (part of the rock group called the Hamilton Shale group and the Mahantango) there are subunits of which the Marcellus is but one. There are publications from the PA Geological Survey about the Marine Devonian (maps, reports etc). The PA Survey is in Middletown PA , with an oil and gas office near Pittsburgh. These reports are available for purchase, and sometimes they are even free.
I beleive that the going rate for Pa gas exploration leasing is about 2500 $ an acre. In louisiana and TExas its much higher (12 K an acre) because theyve already found gas there . If your friend has a lot of land its best to get some advice re: what payments would be realized if gas is struck in marketable amounts. Otherwise, it may be submarketeable but enough to serve a housing compound or farm.
Stereo nets are a tool for visualizing and computer plotting forces acting on folded and fractured rocks. ANy good field structural geology book or geo field manual has information about them, if you are interested I can get you some good intro urls on plotting and using stereo nets. (called Wulf and SChmidt nets)