When they break and engulf chunks of sedimentary rocks, it's called stoping. The original rock layers around subsidence areas are called wall rocks and the layers that xenoliths came from are called parent rocks.One way to find the age of a xenolith or subsidence area surrounded by volcanic debris is to correlate its layers with the layers of wall or parent rocks.Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.
NSF Postdoctoral Research Fellow at Stony Brook University.Adrian Grahams began writing professionally in 1989 after training as a newspaper reporter.His work has been published online and in various newspapers, including "The Cornish Times" and "The Sunday Independent." Grahams specializes in technology and communications.He holds a Bachelor of Science, postgraduate diplomas in journalism and website design and is studying for an MBA. Sedimentary rocks form from soil and silt carried and deposited by moving water.