The position in the time scale of a non-marine formation like the Morrison is difficult to determine unless it can be fixed in some way in a succession of conformable deposits, some of which at least are marine. Geologists have worked along the line of marine succession since the origin of their science, and on this succession mainly the commonly accepted stratigraphic columns and time scales are based. However, after all the excellent work of paleontologists, one of their number informs us that fossils alone too often lead to erroneous conclusions, and that “diastrophism affords the only means of finally attaining a reasonable, accurate, and systematically constructed classification” (1, page 605).a If this be true for marine formations that have been most extensively studied, how much more is it true for non-marine formations whose fossils are often of questionable value in determining age ?
It is safe to say . . .