Final answer:
The Marcellus Shale is the formation found in the Northeast around Pennsylvania, known for its significant natural gas deposits.
Step-by-step explanation:
The formation that is found in the Northeast, around Pennsylvania, is the Marcellus Shale. The Marcellus Shale is a large shale formation that spans much of the Appalachian Basin, including a significant portion of Pennsylvania. This formation is known for being rich in natural gas and has been a significant focus of energy development in recent years. As mentioned in FIGURE 20.2, a Marcellus shale gas-drilling site in Lycoming County, Pennsylvania, is indicative of the prevalence of this formation in the region.