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32 clear that the gravel had not been disturbed. A second one was eight feet below the surface. (Proc. Boston Soc. of Nat. Hist, for January 19, 1881.)

As confirming the entire trustworthiness of Dr. Abbott's observations, it is to be noted that, with a single exception, all the implements reported below the loam which constitutes the surface soil are of argillite, while those upon the surface, which are innumerable, are chiefly of a different type, made from flint and jasper, or of other material of related character. Another fact, which has always had great weight in my own mind, is one mentioned by the late Prof. Carvill Lewis, in his chapter upon the subject at the end of Dr. Abbott's volume on Primitive Industry. I have the more reason to feel the, force of his conclusions, because the proof-sheets passed through Lewis's hands at the time we were together conducting the survey in Pennsylvania, soon after we had visited the deposits in question. The fact was this: Prof. Lewis had been at work for a considerable time in classifying and mapping the gravels in the Delaware Valley, being all the while in ignorance of Dr. Abbott's work until his own results were definitely formulated. But, after he had accurately determined the boundary between the glacial gravels and the far older gravels which surround them and spread over a considerable portion of the territory beyond, he found that the localities where Mr. Carr, Prof. Putnam, and Dr. Abbott had reported finding their implements in undisturbed gravel, all fell within the limits of the glacial gravels, and had in no case been put outside of those limits. Now, Dr. Abbott's house is situated upon the older gravel; but at the time of most of his discoveries he had not learned to distinguish the one gravel from the other. If these implements are all from the surface and had been commingled with lower strata by excavations, landslides, or windfalls, there is no reason why they should not have been found in the older gravels as well as in those of glacial age. There is here a coincidence which is strongly confirmatory of the correctness of our conclusion that there is no mistake in believing that the implements were originally deposited with the gravel where they were found.

Such was the progress of discovery at the time when I began my special investigations upon the glacial boundary in Ohio, and of the glacial terraces there corresponding in age with that at Trenton. To the similarity of conditions along these streams I promptly called attention in 1883, pointing out various places in Ohio where it would be profitable for local observers to be upon the lookout for such evidences of glacial man as had been discovered by Dr. Abbott. The first response to this came from Dr. C. L. Metz, of Madisonville, on the Little Miami River, in southern