STRATIGRAPHY AND THE STUDY OF METAMORPHIC ROCKS
In recent years many students of metamorphic rocks have become so preoccupied with minor structures, structural petrology, physical chemistry, and granitization that the stratigraphy of metamorphic rocks has been neglected. There is great danger that the younger men, indoctrinated with the idea that stratigraphy and sedimentation are unrelated to metamorphic geology, will be inadequately trained to study metamorphic rocks in the field. Geologic maps of regions characterized by different grades of metamorphism should be based on stratigraphy. The assignment of the rocks to formations should be based on the inferred lithology prior to metamorphism and should not be based directly on the present lithology. The student of metamorphic rocks should be familiar with modern concepts of stratigraphy and sedimentation, such as deposition in transgressing and regressing seas, changes in sedimentary facies, and time surfaces. Metamorphic geologists should be familiar with the textures, mineralogy, and chemical composition of sedimentary rocks. When sufficiently large areas are studied, the metamorphic geologist should think in terms of the paleogeography and climatic conditions at the time of sedimentation. Stratigraphers and students of historical geology should realize that their concepts of paleogeography will be incorrect if they neglect the wealth of data to be obtained from metamorphic rocks. These facts can be abstracted from the metamorphic rocks only by intensive investigations in the field by a host of metamorphic geologists well-trained in stratigraphy.