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determination. None of them exceed one-sixth of an inch in diameter. Professor Chamberlin reports having observed a bed containing molluscan shells between the newer and older till-sheets at Greensburg, Indiana. (See Third Annual Report U. S. Geol. Survey, p. 333). Positive evidence is wanting as to whether these fossiliferous silts are of the same age as the silts which cover the district outside the moraine, but they appear to have about the same horizon. No fossils have been found in the silts outside the moraine. It seems not improbable, however, that if originally present their exposed situation is such that the fossils may have been dissolved and removed by leaching.

In the case of streams leading southward from this region of newer drift, careful discrimination is necessary to decide the age of terraces. The coarse, gravelly terraces of the Little Miami valley are referred to the stage when the outer moraine was formed. This valley carried a larger volume of water at that time than in later stages of glaciation, because it was more favorably situated for receiving glacial waters. The Great Miami valley was apparently flooded as much during later stages as at this time, and its gravels are largely of the age of the later moraines. The Little Miami gravels are made up, in large part, of coarse material as far down as the mouth of the stream, pebbles two to four inches in diameter being common. The coarseness of the material testifies to a fair gradient, presumably as great as the present altitude of the country affords. The gravels rise to a height of but fifty to one hundred feet above the present stream, and are near the bottom of the valley trench, for the uplands bordering this stream stand 300 feet or more above its bed. The flood stages, though characterized by a much more vigorous drainage than that which obtained while the silt was being deposited on the bordering uplands, did not reach by nearly 200 feet the limit reached by the silt-depositing waters—a fact which seems to be capable of explanation only on the assumption of great orographic movements.

Deglaciation interval in the later drift series. In his reconnaisance of Western Ohio, some ten years ago, Professor Chamber-