DISCUSSIONS 255

varieties of iron formations are now important sources of crude ore for concentrating plants which assume an ever increasing role in supplying iron ore, needs of the world. Careful mineralogical and text-ural evaluations of iron formations are thus of more than academic interest. It is probably inevitable that terminology which has been extensively used in an area in connection with mining and development will continue to be used. However, the need appears to exist for more precise objective descriptions of iron formations rather than the use of terminology which may some-times be meaningful only to the writer. Since the source of the iron and the silica and the environ-mental conditions which produced major banded iron formations are still subjects for speculation it is understandable that descriptions of field occurrences often to be colored by what is in the writer's "mind's eye " rather than what may be objectively observed. Theories of primary deposition, diagenesis, and later alteration such as recrystallization due to meta-morphism may be involved. However, as Arthur Holmes observed (1965) "It is not always clear where diagenesis ends and metamorphism begins." E. L. BEUTNE