Metamorphic rocks are frequently arranged in zones around igneous intrusions, and each of these zones has certain characteristic minerals by which it can be recognized. Zones of low-grade metamorphism, garnet, kyanite and sillimanite are frequently discernible, and these zones are remarkably similar in different regions, even though the original rocks may have been quite diverse. This similarity in the rocks formed by the metamorphism of igneous and sedimentary rocks suggests that many rocks assumed to be meta-igneous may really be meta-sedimentary in origin.
Proceedings of the Iowa Academy of Science
©1936 Iowa Academy of Science, Inc.
Spivey, R. C.
"Comparative Progressive Metamorphism of Igneous and Sedimentary Rocks,"
Proceedings of the Iowa Academy of Science, 43(1), 253-253.
Available at: https://scholarworks.uni.edu/pias/vol43/iss1/73