32 THE POPULAR SCIENCE MONTHLY. 



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 ob- 

 servations, it is to be noted that, with a single exception, all the 

 implements reported below the loam which constitutes the sur- 

 face 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 men- 

 tioned 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, be- 

 cause 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 classify- 

 ing 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 deter- 

 mined the boundary between the glacial gravels and the far older 

 gravels which surround them and spread over a considerable por- 

 tion 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 coin- 

 cidence which is strongly confirmatory of the correctness of our 

 conclusion that there is no mistake in believing that the imple- 

 ments 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 discov- 

 ered by Dr. Abbott. The first response to this came from Dr. C. 

 L. Metz, of Madisonville, on the Little Miami River, in southern 



