According to the article in Wikipedia®:
“A xenolith (Greek: ‘foreign rock’) is a rock fragment which becomes enveloped in a larger rock during the latter’s development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing lava on Earth’s surface….”
“…To be considered a true xenolith, the included rock must be identifiably different from the rock in which it is enveloped; an included rock of similar type is called an autolith or a cognate inclusion.”
What makes their presence on Monocacy Hill special is their rarity in this area. Discovered at Monocacy Hill by geologist Robert Kulp, they are rare enough to entice him to bring students from California to study these geological phenomena here.
To read further and learn more, we’ve included below links to articles by Robert Kulp, and to maps and photos further detailing the occurrence of Monocacy Hill Xenoliths. For yet more information, contact Helen Brower from MHCA at 610-385-7576 or Robert Kulp via email at RRKANISEPA@aol.com